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An antagonistic insect/host-plant system : the problem of persistence Green, Wren Quinton 1974

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ANTAGONISTIC THE  INSECT/HOST-PLANT  PROBLEM  OF  SYSTEM:  PERSISTENCE  by WREN Q U I N T O N  B.Sc.  (Hons.)  A  f  Victoria  THESIS THE  U n i v e r s i t y of  SUBMITTED  IN  REQUIREMENTS DOCTOR  •  GREEN  PARTIAL FOR  OF  Wellington,  THE  N.Z.,  FULFILMENT DEGREE  OF  OF  PHILOSOPHY  *  in  the  Department of  Zoology  We a c c e p t  this  t h e s i s as  required  THE  UNIVERSITY  OF  conforming  to  standard  B R I T I S H COLUMBIA  February,  1974  the  1967  In presenting  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r  an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I f u r t h e r agree that permission f o r extensive copying of t h i s thesis f o r s c h o l a r l y purposes may by h i s representatives.  be granted by the Head of my Department or I t i s understood that copying or p u b l i c a t i o n  of t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n permission.  Department of The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8 , Canada  ABSTRACT Tansy eaten, of  ragwort  and  the  occasionally  cinnabar  outbreaks  do  manage  that  devastates  of  this  My  to  eradicate  i t s  producing changing  to  a  only  30%  to  survive  regrowth,  in  of  the  fact,  was  Seeds  colonize  habitats,  annual  2. 30-60  production  Female eggs  tansy  moths  on  average-sized  of  a  hence  than  main  tansy the  least  usually  different  cluster  ragwort;  and  at  form.  The  lay  plant.  eat  most  of  the  spacing  population  four-year  British  against  seed  each  of  but  i t s  by:  seed  crop  50%  of  biennials.  (a)  pioneer  seed for  crop  (b) was some  compared were  more  Vegetative  responsible  for  local  species, ensures  to the  colonization.  several  The  surviving  the  biomass  of  clusters  is  of  Columbia.  defoliation;  second  a  study  TyrjLa;  perennials  secondary some  after  Also,  ragwort,  a  herbivore  perennial  process  such  a  became  were  larvae  vulnerable  recover  crop;  controls.  enable  to  so  a  following  plants  the  after  by  is  Nonetheless  can  Nanaimo,  normal  defoliation  persistence. new  a  how  a b i l i t y  growth  .  does  resistance  crop  defoliated  How  weed,  areas,  persist  near  i t s  of  (L.)}  follows  effective  biennial  large  likewise,  system  seed  size  plant.  as  a  over  supply  are  perennial  the  the  and  on  second  experimentally  likely  no  depends a  10%  has  L.),  jacobaeae  food  conclusions  persistence  with  (T_yria  persist?  Ragwort  jacobaea  defoliated  herbivore-plant  1.  only  moth  not  plant  crashes?  (Senecio  clusters larvae the  from  of an  average  adaptive,  and  i i  at  low  moth  resource. clusters large  densities At  is  have  overloaded biomass),  clusters the  food  These  on  to  moths  some  food  plants  have  the  moth  starvation,  since  they  provide  dispersing  larvae  that  find  instar  density-dependent,  75%  of  that  particular  more  i s  p l e n t i f u l ,  the  food  larvae  reaching  a  20%  of  5.0  plants/m .  food  distribution  of  ovipositing  on  many  plants  that  plants  are  exceed  the  clusters.on  adequate  them. and  plant  them,  and  i s  for  once  in  one  during  in  than  before, high:  plants  through for  the  the  f i f t h  with  also  f i f t h  had,  an  disperse  0.5  In  average,  the  risk  plants/m  compared  over  instar.  on  although at  for  population  the  dispersal  found  food  Larvae  dispersed  larvae  crash  associated  that  sometimes  suggest,  Dispersal  behaviour.  however,  was  I  populations  larvae  plant  fifth-instar  important,  when  dispersed  study  after  not  with  of  only  2  80%  at  2  From conditions own  are  'head-flicking'  food  the  refuges.  maintaining  when  no  of  against  requirements  refuges  antagonistic  prefer  Consequently  food  is  the  discriminate  them.  larval  use  however,  since  f a i l  whereas  become  3.  and  (i.e.  efficient  densities,  contagious,  plants,  already  thus  high  promotes  these  populations  numbers  under  observations  other  before  a l l  of the  conditions  the  I  cinnabar  host they  conclude  plants cannot  that  moth are do  can  under  some  regulate  their  stripped,  so,  and  but  crash  that  through  starvation, that  larvae  condition on this  A  plant idea.  proposed insect  necessary suffer  that  i s  for  with  from  essential the  species.  associated  l i t t l e  satisfied  density The  condition  11  Outbreaks high  an  mortality when  plant  outbreak  features  cinnabar  for  moth in  host-plant  of  outbreak during  density  areas the  are  seems  be  these  is  high.  consistent  \  a  Data with  mechanism  identified  species  densities.  be  dispersal,  regulatory  could  to  in  were  other also  iv  TABLE  OF  CONTENTS  Page  ABSTRACT TABLE  i  OF  CONTENTS  iv  LIST  OF  FIGURES  v i i i  LIST  OF  TABLES  x i  ACKNOWLEDGEMENTS GENERAL THE  x i i i  INTRODUCTION  I N S E C T / H O S T - P L ANT (A)  CINNABAR  The  Imago  The  Larval  TANSY  I.  6 6  And P u p a l And  8  Disease  RAGWORT, And  Stages  10  SENECIO  JACOBAEA  L.  . . . . . . . . . . . .  Distribution  14 15  Importance  21  AREAS  RESPONSE  12 12  Habitats  Economic  PART  (L.)  History  Plant  STUDY  JACOBAEAE  And D i s t r i b u t i o n  Description Life  6  7  Parasitism (B)  1  SYSTEM  MOTH, T Y R I A  Systematics  THE  . . . . . .  24 OF  SENECIO  JACOBAEA  TO  DEFOLIATION  ...  31  INTRODUCTION  31  METHODS  34  Summer  Growth  34  Defoliation Secondary Changes  Experiments  Seed  In  34  Production  Form  And  37  Distribution  37  BESULTS Pattern  39 Of  Synchrony  Summer Of  Growth  Larval  Defoliation  And  Defoliation  And The  Size  Of  Form  And  Feeding  Secondary  Secondary  39 With  Growth  ....  Growth  Perennial  And  Plant  Normal  45  Response Seed  Distribution  . . . . . . . . . . .  Crops  After  Repeated 54  DISCUSSION II.  48 50  Defoliation  PART  43.  65  STRATEGY  FOR  PERSISTENCE:  THE  ADULT  STAGE  ....  74  INTRODUCTION  74  ADULT  76  DISPERSAL  Introduction  76  Method  77  Results  78  SIZE  OF  EGG  CLUSTERS  RELATIVE  TO  PLANT  BIOMASS  Introduction Method  86 86  ..  87  Results CLUSTER  ....  88 VARIABILITY  AND F I R S T - I N S T A R  SURVIVAL  100  Introduction  100  Methods  101  Results  .  102  vi  NUMBER  OF  CLUSTERS  PER  PLANT  AND L A R V A L  SURVIVAL  ..  Introduction  111  Method  112  Results  114  SPACING  OF  CLUSTERS  BY  FEMALE  TYRIA  116  Introduction  116  Methods  116  Results  118  FACTORS  INFLUENCING  CLUSTER  SIZE  124  Introduction  124  Results  125  DISTRIBUTION  OF  CLUSTERS  AND  PLANT  OVERLOADING  ....  Introduction ,  129  DISCUSSION III.  145  STRATEGY  FOR  PERSISTENCE:  THE  LARVAL  STAGE  ..  INTRODUCTION DEVELOPMENT Field EFFECT  159 159  OF  AGGRESSIVE  Observations OF  127 127  Results  PART  111  CROWDING  And ON  BEHAVIOUR  . . . . . . . . . . . . . . .  161  Experiments  . . . . . . . . . . . . . . .  161  LARVAL  DISPERSAL  . . . . . . . . . . . .  166  Introduction  166  Method  167  Results  167  FREQUENCY  OF  DISPERSAL  IN  A  NATURAL  POPULATION  ....  171  Introduction  171  Method  171  v i i  Results EFFECT  172  OF  PLANT  DENSITY  ON D I S P E R S A L  SUCCESS  . . . . . .  184  Introduction  184  Method  184  Results  185  LARVAL  BEHAVIOUR  DURING  DISPERSAL  188  Introduction  188  Method  188  Results  190  REGULATION  AND L A R V A L  DISPERSAL  DISCUSSION GENERAL  DISCUSSION  LITERATURE  CITED . . . . . . . .  -  A HYPOTHESIS  ....  194 199  .•  210 226  APPENDIX  1.  235  APPENDIX  2.  238  APPENDIX  3.  241  APPENDIX  4.  243  APPENDIX  5.  246  v i i i  LIST  OF  FIGURES  Figure  Page  1  Location  2  Map o f  the  3  Growth  of  4  Seasonal change in biomass of Senecio jacobaea and the synchrony i n development shown by f i f t h - i n s t a r l a r v a e  42  Secondary growth and regrowth J§22^aea plants as a function of d e f o l i a t i o n .  46  5  6  map o f  River main  the  study  and C l e a r b r o o k . Chase  locations  during  Regrowth June stems  River  Senecio  study  jacobaea  areas area  Chase  showing  flowering  of perennial 1971 after i n September between  number  8  Relationship available  biomass  9  Relationship  between  10  Comparison  11  D i f f e r e n c e s i n wing l e n g t h between a d u l t male T y r i a jacobaeae of ages f o r three l o c a t i o n s  biomass  available  biomass of  single-stem  of  on r o s e t t e  between  Senecio the time  and b i e n n i a l p l a n t s in production of secondary 1970.  Relationship available  of of  the  plants  t h e ~ s u m m e r ,~1 9 7 0 ~(n=17)  7  12  at  number  leaves  plants.  of  on s i n g l e - s t e m number  of  on multi-stem  biomass  of  and multi-stem  leaves  and and  plants.  leaves  plants.  flowers  plants.  ....  and  .....  between  samples of different  D i f f e r e n c e s i n wing l e n g t h between samples of adult female Tyria jacobaeae of d i f f e r e n t ages f o r three l o c a t i o n s .  13  Winglength  14  Survival  as of  a  in  male  function  the  of  of  and female pupal  f i r s t - i n s t a r  number  of  eggs  Tyria  jacobaeae  length  larvae  as  hatching.  a  function  . . . . . . . . . . . . .  25 26 41  51  58 59 60 63  81  82  83 105  ix  15  Survival  and  larvae 16  Height  in  at  18  Survival  21  22  23  24  26  27  28  of  the  and are  grouped laid  of  Tyria  conditions.  relative  to  of  from  on  109  from the  eggs  of  emergence  The  The  106  the  different  numbers  the for  Tyria and  110  of  plant.  115 as  wing  a  function  length.  of  . . . . . . . .  Effect of age o f f e m a l e T y r i a moths on (a) t h e number o f eggs l a i d p e r cluster, and (b) the number of mature eggs retained after oviposition The  ..  plant.  larvae  Development  122  123  e f f e c t of d a i l y variations in sunshine and t e m p e r a t u r e on t h e r a t e o f o v i p o s i t i o n and s i z e o f egg c l u s t e r s .  126  observed and egg c l u s t e r s on when a l l plants attractive  133  expected d i s t r i b u t i o n s of t a l l S. jacobaea plants a r e assumed t o be e q u a l l y  o b s e r v e d and expected distributions of egg clusters on t a l l S. j a c o b a e a plants when a l l l e a v e s a r e a s s u m e d t o be equally attractive  Relationship on  25  eggs  clusters  time 20  development  R e l a t i o n s h i p between c l u s t e r h e i g h t above ground and the l e n g t h of time needed egg development  egg 19  of  of  solitary  which  height 17  rate  each  between  plant  Relationship on each clumps.  and  the plant  between the plant and  number  of  clusters  density.  number of the size  P r e d i c t i o n s from a model of the eggs on overloaded plants s i z e is changed.  136 of  clusters plant  proportion of when cluster  Rate of dispersal from enclosed plants by fifth-instar larvae starting at three density levels Effect  of  larvae  plant to  locate  density a  new  on host  the  134  a b i l i t y  plant  in  of a  137  155  169  X  grazed 29  30  Line of travel the p o i n t of radius Overwintering weight  31  pasture.  Flow  186  o f 57 f i f t h - i n s t a r l a r v a e crossing a circle of  survival  of  pupae  according  at 1m to  class.  diagram  processes  202  indicating that  193  affect  the  major  numbers  behavioural in  Tyria  214  xi  LIST  OF  TABLES  Table 1  Page Weather  data  Abbotsford 2  Seed  for Airport  production  defoliation, 3  4  5  6  7  A  9  10  11  and  plants by  after  . . . . . . . .  27  complete  comparison of the proportion of multistemmed plants from areas with, and w i t h o u t r e p e a t e d d e f o l i a t i o n by T y r i a . . . . . . .  57  non-defoliated  Effect of l a r v a l d e f o l i a t i o n clumping in different Senecio jacobaea .  plants.  on t h e d e g r e e communities  of of  64  A comparison of the frequency of oviposition by T y r i a on r o s e t t e s and stemmed p l a n t s o f Senecio jacobaea  90  Frequency of o v i p o s i t i o n on plants when the height relative to that of vegetation.  91  Size  of  egg  Estimated plants, plants.  clusters plants  at  biomass and p l a n t  laid Chase  Senecio jacobaea is considered the surrounding on  rosettes  River,  and  1971  92  of rosettes, stemmed clumps plus individual  95  P r o p o r t i o n of plants with s u f f i c i e n t food f o r the f i f t h - i n s t a r l a r v a e s u r v i v i n g f r o m an average-sized cluster The  estimated proportions of egg clusters laid on p l a n t s t h a t were l a r g e enough to f e e d t h e l a r v a e from an a v e r a g e c l u s t e r to pupation.  Effect  of  Effect  of  instar 13  by  parentheses).  and  52  instar 12  (in  Airport  ..  stemmed 8  Nanaimo  Effect  of  cluster  size  on  egg,  and  egg  height  on  egg,  and  f i r s t 108  clusters site  99  103  survival.  oviposition  '  f i r s t -  survival cluster  96  by  on  the  female  choice Tyria  of  moths.  an .....  124  x i i  14  Distribution  of  Jacobaea 15  16  17  18  20  22  23  24  per 130  to be on requirements instar are  139  141  Proportion of eggs estimated to be on overloaded plants when f o o d requirements t o the end o f l a r v a l f e e d i n g a r e 0.744 g per l a r v a  142  Distribution of  Number of during six densities plant Dispersal  of  egg  eggs  clusters  per  according  to  the  cluster.  157  fifth-instar larvae remaining days on plants with i n i t i a l of 5, 15, or 50 larvae per  rates  of  fifth-instar  larvae  170  of  ages  175  Number o f f i f t h - i n s t a r l a r v a e d i s p e r s i n g f r o m rosettes and stems as (a) their f i r s t move; (b) t h e i r s e c o n d move  178  Number o f f i f t h - i n s t a r l a r v a e d i s p e r s i n g f r o m overloaded, and non-overloaded, stemmed plants  181  (a)  A  The p r o p o r t i o n o f d i s p e r s e r s t h a t improve their chances of obtaining food; (b) the numbers of dispersers that diminish, i m p r o v e , o r do n o t a l t e r , t h e i r c h a n c e s of obtaining food. l i s t areas  25  clusters  Proportion of eggs estimated to be on o v e r l o a d e d p l a n t s when food requirements to the end of l a r v a l f e e d i n g are 0.440 g per l a r v a .  different 21  egg  Proportion of eggs estimated overloaded plants when f o o d to the end of the fourth considered.  number 19  Tyria  plant.  of  S.  jacobaea  coincident  densities  with  T_yria  in  different  outbreaks.  . . . . . .  Effect of dispersal mortality on a hypothetical population of fifth-instar larvae  f  183  197  207  ACKNOWLEDGEMENTS I  was  ecology his  of  attracted my  helpful  earlier  the  supervisor,  drafts.  people  l o g i s t i c s  at  of  H.R.MacCarthy, frequent thanks Cinnabar brewing  appreciated -  criticisms Chris  Carl  both at  my  of  1972.  Gail.  To  sincere could  my  family  in  for  and  thank  I  support,  and  improved  as  of  particular  I  am  who,  cheerful  him  for  comments a  in  and roam  to  on  result. eased  grateful spite  to  of  my  generous.  me  for  hospitality  her  approach  Agriculture  letting  advice by  in  s t a t i s t i c a l ,  Neil and  so  My  freely  over  and  ever-  B i l l  so  Lauriente  Clark,  the  and  me  and  grammatical,  Gilbert.  N.R.Liley  proposals  Dolores  on  -  assisting  H.R.MacCarthy,  a l l  earlier  made I  thank  during  summer  programming  other  students  polydeterministic  helpful  drafts.  competently  for  and  help,  who  and  worked  so  Model,  I  encouragement  of  Cinnabar  thanks.  always  W Bench:  A l l ,  and  Wilkinson,  Marge  me  research  Walters,  I  Group  In  for  P.Harris,  enthusiastically offer  ideas  Department  unfailingly  the  given  Sanderson in  Chitty,  much  Fred  to  the  kettle.  G.G.E.Scudder,  to  was  and  is  work.  to  by  financial  Canada  Garner  Valley,  practical  work  the  and  Joe  tea  I  Dennis  It  f i e l d  requests, to  U.B.C.  c r i t i c i s m s ,  thesis  Several  to  a  rely  distant  Jon  their  on  and  own  the New  Lynn,  ways,  unquestioned Zealand Louie  helped  and  and me  a  those  good  Christy, great  deal.  friends  Dick  and  Finally,  xiv  a  warm  'thank  stimulated  and  you'  George  starting  a  afternoon.  the  broadened  particularly with  to  my  Calef,  photograph  A biologist,  many  of  graduate  students  understanding  who red  gave  me s o m e  leaves  W.M.Wheeler,  once  taken put  of  who  ecology,  valuable one that  cold  lessons spring  lesson  words: " W e s h o u l d a l l b e h a p p i e r i f we w e r e l e s s completely o b s e s s e d by p r o b l e m s and somewhat more a c c e s s i b l e to the e s t h e t i c and e m o t i o n a l a p p e a l of our materials, and i t i s d o u b t f u l whether, i n the e n d , the growth of biological science would be appreciably retarded."  s  have  in  1  GENERAL  INTRODUCTION  Over majority of  each  the  span  of  species  species  through  the  rate  evolutionary is  depends  adverse  of  biologists  where  the  interest  1973),  or  a  proximate Connell  factors 1961).  as  In  i t s  and  of host  two  prey,  the  long-term exploited  balance  at  the  expense  resistance Beck  (1965)  is  by  and  I  of the  the  reviewed  the  the  to  host,  w i l l  long-  To  study  (e.g.  interest  adopt and  is  Cody  in  the  change  (e.g.  primarily  should  adaptations a  of that  not,  an be  and  persistence  faced  by  exploiter  in  and  the  any  depress  numerous  (the  insect  insect)  predator a the  relationship  as  population  comes  development  insect's plants  of and  subsequent  ways  by  maintenance  this  the  favour  insect  the  describe  that  particular  encountered  namely,  the  shall  plant,  not,  between  increase  plant  i s  problem  between  a  approach,  explanations  shall  new,  other.  similar  since  i t  1.0.  observed  adapt, to  maintains  the  vast  can  evolutionary  an I  examine  The  plant).  'antagonistic',  for  the  persistence  i t  than  where  study  the  I  parasite  (the  approach,  although  plant.  less an  of  selection,  i t  ultimate  association  species or  not  in  from  which  that  adopt  this  study  so  account  approach,  this  single  these  In  at  fate  continued  natural  of  is  the  The  rate  of  may  that  d i s t i n c t  persistence  the  effects  mechanistic  evolutionary treated  on  increase  populations  time  extinction.  mechanism  unpredictable, term  of  growth  resist  of  rate. insect  2  attack. The plant  to  have  on  two  persist, the  strategies  from  (Southwood  1966),  on  I  (!••)#  usually  regarded  been  a  'The  other  and  against  research  dependence  effect  of  Raven  feeds  a  species  the  a  problem  of  features  released tansy  animal the of  larvae  the  evolutionary  association  populations  were  as  a  S.  jacobaea  to  size  useful  (Lack on  1954;  butterfly  l i f e the  moth,  in  plant  outbreaks  tansy  which  is  land.  The  under  moth,  the  which  biological  had  control  1965) ,  interested  me  reasons.  F i r s t ,  the  for  history), two  detail  The  Tyria  on  agricultural  (Wilkinson  between  subject  in  major  insect's  Schoener  migration  exclusively  two on  of  cinnabar  System'.  l o c a l l y  for  via  theoretical  1968;  chemicals  described  ragwort  ecology  strategy  biennial  weed  are  may  1964).  almost  L.,  one  provided  clutch  and  respective  from  have  plant  was  to  Levins  the  optimal  studied  as  as  1972),  jacobaea  both  1967;  insect  their  attention  who  Insect/Host-plant  imported  measure as  of  Wilson  the  effects  as  approach  phenomena  which  Senecio  considered  This  and  enable  detrimental  ecologists  the  that  receiving  (Ehrlich  insect  the  be  and  such  and  ragwort,  heading  is  Dingle  patterns  cycles  of  can  f i e l d  1962;  JS£2^§®5§  l i f e  spite  survival.  generalizations  The  adaptations  (MacArthur  and  feeding  in  strategies',  ecologists  Cody  of  other,  for  •adaptive  1972),  sets  food  (as  well  indicated  species. that  a  Yet  increased  as  long some the  3  probability  of  evolutionary severity  of  time such  resistance  that  obviously  Indeed,  the  moth  population  early  emergence  food,  some  S.  jacobaea,  sort  of  gives  no  system  The cinnabar  the  of  such  was  How  so  major  be  the  food of  the  moth  to  plant  s t a b i l i z e  study  against  He  in  was  small the  largely  adaptive  strategy  then  this  had  in  with the  high  matter  to  extinction  fraction  very a  appears  referring  with  the  ragwort,  present  areas  associated  on  tansy  which  heterogeneity  habitat."  is  the  regulatory  act  and  factor  a  plant  regulatory  no  detailed  population  that  the  supply.  cinnabar  the  in  However,  and  Over  reduce  other  might  a  only  to  increase  resistance,  survive  some  moth.  survived  moth  moth.  individuals  probably  the  second  could  is  heterogeneity  of  the  heterogeneity  indication  part  stages  in  by  This  plant  and  the  would  upon  Heath]  to  population  some  the  shortage  of  by  "The  and  covered  the  of  wrote,  food  or  that  1935).  expected an  conclusion  [Weeting  of  of  be  by,  proposed  limits  dynamics  the  time  effective  the  (1971)  either  directly  (Cameron  would  1968),  been  at  population  the  acts  had  below  buffer  selection  outbreaks  lacks  mechanisms  Dempster  extinction  (Pimentel  mechanism  numbers  local  of  of  intimate  to  at the the  adequate large  of  the  area moth  mortality. chance,  and  survival  on  insect-host  long?  feature ease  observed.  which  with Many  interested  which  f i e l d  studies  me  in  behaviour of  in  the a l l  vertebrate  4  populations regulating behaviour  have  shown  numbers is  (see  also  populations  and  regulating  cinnabar  finding  the  and of  active  in  the  enough  (up  to  by  role  behaviour  daytime;  at that  play  Moss  1971).  the  was  in  larvae  moths  parasites,  in  larvae  plants  be  in  control  traits and  time  can  insect  interested  the  in  while  ineffective  I  same  role  of  As  behavioural Both  a  1970),  regulation  played  of  plant.  tall)  and  populations,  host  1.5m  can  frequently  importance  the  the  Cammell  were  moth  Watson  in  and  disease  the  u t i l i z a t i o n  review  Way  predators,  numbers  behaviour  important  (e.g.  out  that  are  watched  in of the are  small without  d i f f i c u l t y . After study  to  moth  one  examine  on  the  'succssful plant  the  be  affected  the  1  as  a  of  of  work  i f  Tyria  defoliation  i t s  insect  on  host  adopted  the  by  at  the  This  extended the.  plant.  persistence  consequence.  I  cinnabar  Clearly, expense  of  work  the  is  the  of  plant  presented  any the was in  I.  expansion, density  the how  hence  regimes  individual  see  f i e l d  effects  short-lived  Populations  by  of  survival  strategy  would  seriously Part  summer  in I  could  and  see  survival.  female this  my  moth  study  were  investigate how  In  Part  i n  the  strategy  area  the II  in  different  behaviour  behaviour I  examine  distribution  affects  of  under  different  patterns  affected  the of  stages  strategy  her  individual  eggs,  adopted and  success  then and  5  population the  s t a b i l i t y  behavioural  shortage, and  the  plant  was  of  this  was  an  i t  i n t r i n s i c  is  would My  to  of  summarized  the  not  a  as  identify  have  i t s  conclusions  the  in  the  General one  this  point  to  I  examine  and  the  are  in  food  individual  this  in  species, The various  study,  herbivore the  not  and  the  maintenance  heterogeneity  referred  an  to  extrinsic  importance  of  discussion  this  sections,  Discussion.  result  success  the  role  The  each  conditions  greatest on  both  environment.  that,  to  of  system.  outlined  III  crowding  subject  important  of  to  Part  advantage  primary  an  feature  In  population.  play  the  hoped  the  response  in  I  of  for  rises.  larvae  the  the i s  of  terms  herbivore/plant  heterogeneity  able  was  in  found  feature  and  in  consequences  heterogeneity  density  response  again  although  as  under as  a  of  this  which  study, the  biological  summarized  in  I  would  cinnabar control Appendix  be  moth agent. 5.  6  THE  INSECT/HOST-PLANT  (A)  CINNABAR  MOTH, When drew of  the hind  cinnabar  in  named  wings  this  moth  (L.)  i s  a  member 6,000  polyphagous  1758, although  the cinnabar between  and r e d m e r c u r i c  exceeding  coloured,  JACOBAEAE  to the similarity  moth  assemblage  TYRIA  and D i s t r i b u t i o n  Wilkes  attention  SYSTEM  the  species,  species.  only  of  i n  1773 he  the vermilion  colour  sulphide,  or cinnabar.  The  Arctiidae,  an  Family including  Linnaeus  the s p e c i f i c  moth  described  name  many  brightly  the  species  of jacobaeae  has  been  literature,  and  retained.  Four  generic  are  listed  the  dates  1807),  the  of  Kloett the  of  their  British  name,  misspelling.  lIEiii  names  Hincks  generic  throughout  1828).  Insects  generic  and  I  this  as  (1972)  shall  been  used  i n  Zoologicus  the  (Neave  publication 1809),  Kloett  (1945),  and noted  omitted  listed  refer  to  Hyjagcrita (Huebner  and H i n c k s ,  synonyms.  that  Ty,ria  1939),  i n  Euchelia  (Huebner  1819),  their ,  with  and  Check  and  listed  In  their  revised  edition  only  Tyria  Huebner  1 8 1 9 , as  jacobeae the  has  appeared  cinnabar  moth  as  as  a  Tyria  thesis.  l .£2J2 .®§.s a  f i r s t  (Latreille  (Boisduval  other  have  the Nomenclator  Callimorp_ha  Euchelia ; ——— List  i n  names  a  i-  s  widely  distributed,  from  Ireland  7  throughout 1903;  Meyrick  map  of  was  most  in  abundant where  Maritime  Europe  1968).  Tyria  absent the  mainland  the  Dempster  England in  the  s o i l  Provinces since  agent  against  Senecio  Victoria,  western (1971)  i t s  which  and  on  jacobaea.  Australia(Bornemissza  a  as  a  and  now  west  1964;  occurs  in  coast  of  control  Frick  were  New  moth  usually  biological  introductions  (Kirby  the  was  Tyria  (Harris  1966),  that  and  the  Asia  distribution  showed  drained.  introduction  Unsuccessful  central  counties,  poorly Canada  and  compiled  Wales  southern  of  America  1964).  and  was  North  Holloway  to  and  made  Zealand  in  (Miller  1929).  The  Imago  Tyria patterns or  and  unusual colours  vermilion  costal a  is  streak  shorter  on  vermilion  spots  1968).  c i l i a  black.  The  average,  having  yellow  usually  the  with  sides  of  the  of  hind  greyish-black streak  below on  Lepidoptera  both  the  larger  and  instead  along  the  apex  wing,  wingspread  Kirby(1903) with  on  colouring  vermilion  The  among  is  the  having  wings.  wings,  the and  to  inner above  thorax, 45  mm,  refer  to  identical  The  appears  cinnabar, a  sub-  which  also  have  margin  and  two  fore-wings,  head, 30  in  the  in  tornus  and with  (Meyrick  abdomen the  males,  are on  wings.  S o u t h (1961) of  vermilion  orange-yellow  rare  markings.  colouration,  individuals This  appeared  variant, in  the  8  cinnabar than  moths  0.01.  at  These  Robinson(1971), the  at  mutant  could  variants  probably  owing  England  (Cameron  (Hawkes  Each surface  female of  and  average as  160  entire  egg  interaction  The The  instars, days  male.  red  with  varies  differences  in  pigmentation  red  that  from  a  place  of  mutant similar  to  place,  temperatures.  late  May  California  emerge  by  to  pigmentation.  spring  moths  less  According  controlled  in  of  between  and  June  where  mean  mid-April  and  1968). lay  several  jacobaea feed,  a  on 35-50  cluster.  1935),  and  for  Arctiids  higher,  in  and  egg  leaves. S.  vulgaris  The  eggs in  the  are  a  lower  eggs  (groundsel). I  have  yellow,  about  within  on  Occasionally  eggs,, although  hatch  hatches  clusters  10-13  day  The  found  0.65  mm  days.  with  no  are  as in The  obvious  larvae.  Pupal  take  3-5  frequency  suggested  in  between  larvae  to  i s  Bragg  cluster  Larval  he  emergence  contains  eggs  yellow  Fort  larvae  cluster  normal  emerge  Senecio  the  the  a  always  moths  may  diameter(Cameron  8-11  of  with  the  at  are  nearly  species;  adult  of  B.C.,  by  those  part  1935);  Hay  l a i d ,  of in  some in  most  temperatures early  for  occur  time  five  are  replacement  least  The  many  River,  Zygaenids(Lepidoptera)  genes,  In  Chase  approximately  days the  Stages  for f i f t h  each  of  instar.  one  month  to  the  f i r s t  four  The  larvae  pass  are  through  instars,  and  essentially  9  monophagous  on  genera  the  found S.  in four  jacobaea  On tissue  of  move  the  instars  Besides  on  the  Host  of  black  of  dark,  enclosed  period  the  of  generation  feed and  for  on  other  Harris  (1961)  development  cineraria  the  a  to  that  larvae  s o i l  D.C.,  year,  to  project  may  :  and  S.  and  the  the  both  or  site stumps.  my  The  the  the  larvae  in  large  of  subsequent the  plant,  with  have  and  age. black  sideways.  host  plants  and  sites  are  vegetation,  ground  under  study pupae  colour.  the  spent  is  In  banding  stones,  reddish-brown winter  the  often  Pupation  above  During  decreases  foward  under  leaf  and  larvae  left  in  top  lower  black  leaves.  steadily  be  and  feed,  mid-July.  surface,  a  near  had  the  develop,  they  bands,  and  tree  yellow to  on  leaves.  young  remain  by  pupation  rotting  and  studied  sites  feed  adjacent  where  black  areas,  hours  larvae  aggregations  hairs  common in  buds  and  pupation  beneath  galleries  S.  starts  plant,  tend  the  to  instars  the  yellow  out  A  suitable  L.,  pale-green  flower  sought  bark.  of  larvae  size  and  w i l l  Bucher  characteristic  later  top  the  the  were  vulgaris  disperse  the  the  clusters,  Senecio  the  rarely  pattern to  they  Senecioneae.  S.  hatching, and  of  though  Michx.  instar  just  tribe  L.,  second  heads  jacobaea,  species  Eaup_erculus  but  S.  in  area  was  harden There the  is  tree insect  over only  pupal  a one  stage.  10  Parasitism  and  Disease  Cameron(1935) Tyria, a  though  brachonid  4%  in  study in  by  (1971)  year  outbreak  of  populations. i t  was  Bridg. by  40-50%  Wimereux,  I  was  thus  Assessing  the  role  a  rate near  of  A.  A.  rate  a  f a c i a l i s , on  60$  rose  as  high  preventing  was  was  Tyria  in  the  an  Tyria  f a c i a l i s  not  1928  as  d i f f i c u l t ,  measured  hyperparasitism in  a  density-  H§sochorus  and  of  attack  s t a b i l i z e  attack  A.  Dempster  inversely  £oj3u^aris  of  recorded  £°£ularis  no  i n s t a r s .  were  found  These  were  usually  only  year.  to  hyperparasite  M.  next  in  by  rate  found  sand  of  a  40%  dunes  at  Boulogne.  found  larval  of  which  reported  a  an  unlikely  whose  by  as  also  is  rates  that  ineffective  i s  by  the  He  of  Britain  measured  £2£ularis  act  and  J22£ularis  have  low;  to  Tyria,  area  was  A.  D a v i a u l t (1929)  A.  parasitism  larger  by  It  Great  parasitism  found  parasitism  (Ichneumonidae),  on  who  attack  tended  of  1932.  no  attacked  Dempster.  4155 i n  parasites  Haliday,  (19 35)  by  and  factor.  rate  stated),  followed  in  ^opularis  Cameron  1 9 3 1 , and not  Ichneumonid parasite  The  widely;  in  that  1969  important  larvae.  (date was  found  -dependent  as  5%  several  Ajganteles  fluctuates  Lyle  in  most  young  1930,  one  35%  the wasp,  parasitises pogularis  l i s t s  two  with  references Only white  found adult  a  late  few eggs in  Ichneumon  to  large  common  larvae  attached the  to  summer.  wasps  parasites  of  the  in  my  larval  Larval  of  the  study skin.  parasitism  different  species  11  emerged These  from  pupal  species  had  cases  not  out  of  several  previously  hundred  been  recorded  suffered  from  reared  pupae.  from  western  f a i r l y  intense  Canada. f.I£ia  appears  parasitism few  in  New  of  fll3EiSS£§ Tyria  data  adult  Selys,  to  1938;  the  shining  and  New  largely  1966).  In  and  the  appears  to  predators.  Neither  Cameron(1935)  on  the  during  the  egg  stage.  area:  a  found and  every was  mite year  eggs, The  Balaustium sucking  responsible  Dempster  sp.  yolk  for  was  near  from  a  egg  failure and attacked  well  as  of Fyfe  by  to  by the  parasites  Dempster(1971) recorded  low  similar  in  murorum  eggs,  very  was  loss  nor  situation  major  1970).  l i t t l e  and  the  (Carrie  as  a  are  Har^obittacus  for  Tyria  parasites,  There  red  Zealand  there  Australia  mecopteran  populations New  be  In  responsible  starlings(Miller  parasites  although  Zealand.  larva,  hymenopterous  cuckoo  Australia,  permanent  Bornemissza and  and  from  was  establish  tachinid  have  Zealand  quantitative  predator  to  was  small  or  found  mortality my  study  (F.Erythraeidae) never  abundant,  proportion  of  egg  mortality. Lepidopteran microsporidian H a r r i s (1961)  larvae  and  v i r a l  screened  larvae  died  from  genus  losema  are diseases.  Tyria  infections  Nageli  during  stocks by  a  their  often  susceptible  For  reason  Bucher  release,  as  this  before  microsporidian feeding  species  t r i a l s .  A  to and many of  the  polyhedral  12  virus  destroyed  a  major  portion  Australia(Bornemissza  1966),  rearing  adopted  conditions  he  D e m p s t e r (1971)  found  Weeting  Heath,  peak  microsporidian appeared year  in  these  in  and  and  largest  RAGWORT,  SENECIO  shrubs  one  has and  a  a  many  Senecio with  and  single  raised  in  1972.  as sp.)  In  the both  is  a  in  Similar  caused a  same  preventive  field-collected  and  A  infection  disease.  being  at  starved.  larvae  the  the  diseases  Stringent  from  JACOBAEA  Senecio the the  jacobaea  Family  major  world-wide weed  jacobaea stem  viral  crowded  by  polyhedral  eggs a virus  L.  Distribution  in of  a  into  spread  larvae  f i f t h - i n s t a r  foseraa  comm.).  ragwort,  constitutes  populations  to  these  many  probably  identified a  when  controlling  larvae  pers.  genus  of  evidence  experiments.  in  (probably  Description Tansy  in  were  (B.J.Campbell,  TANSY  plot  a r t i f i c i a l l y  no  destroyed  f i e l d  the  imported  helped  years  area  larvae  undoubtedly  was  ineffective  microsporidian  Senecio  study  appeared  1973,  (B)  what  my  were  symptoms  and  diseases  laboratory measures  in  the  although  disease.  even  of  L.,  member  Compositae,  groupings  of  distribution,  which the  and  of in  the turn  Angiosperms. includes  some  species.  is  that  a  biennial  branches  or  into  perennial a  herb,  terminal  usually flowering  13  cluster.  The  subsequent  leaves  the  lower  leaves  leaves  may  underside. varying 15  ray  or  hairs,  the  are  of  a  in  as  to  florets  involucral  have  lose  cup  of a  the  u n t i l  as  edges.  long  flowering  cluster  each to  capitulum  60 d i s c  the  f r u i t ,  low  •parachute . pappus, are  and  the  on  consists  seed  a  12  to  f r u i t ,  a  mass  a  the  dispersal and  achenes  loose  shaken  of  These  separate  remain  eventually  of  end.  as  they  of  Each  with  and a c t  and  hairs consists  However,  1  leaves  The  d i s t a l  humidity  blunt;  petioles.  f l o r e t s .  single  to  and  Rosette  sparse  the  they  ovate  short  attached  long  form  40  are  have  hard-walled  conditions  outwards  plants  capitula;  dry,  leaves  indented  yellow  pappus,  twice  mechanism;  ray  not  surrounding  i s  bend  may  number  more  stemmed  The b r i g h t  florets  hairs  have of  or  achene,  fine  the  first-formed  of  in  out  the (Green  1937).  In  a  Harper Great  major  and  Wood  Britain.  florets,  Of  has  wide  thosec  vulnerable  to  from  human  weed  var.  the  -  varieties  Sweden  Europe, and  have  specimen. in  a c t i v i t i e s It  Senecio  varieties  a l l  type  of  as  discoideus  remaining  species.  continental  southern  four  d i s t r i b u t i o n , owing  following  throughout  than  biology  l i s t  and condensata  leaves  very  the  these, the  segmented a  on  (1957)  while  §£en22i2§§!iS»  i  work  is as  Denmark  The  into  east  in ray  abrotanoides,  plant to  leave  present far  lacks  narrower  part  that  occurring  L. -  'jacobaea,  from  more  currently  i t s land  as  or  spread open  Ireland,  Siberia,  northern  and  and  Greece.  14  §•  Ji£2£S§§  in  the  introduced  s  and  in  introduction by  into  to  1957).  A  paper  are  two  distinct  stage  and  normally  become  established  may  l i e  following  spring  overwinter  as  few  season  110  cm  (1972  the  second-year in  a)  South  the  does  America map  not  other  1935).  rosettes the  adding  plant and  with  of  show  any  introductions  a  to  form  the  Seedlings  September,  although  winter  to  in  germinate  germinating  f u l l more  first-year  plant.  extensively  Starting  unbranched„  branch  the  f i r s t  produces  and  Seeds  several  form.  stages:  flowering  August  (Cameron  growth  stems  August  branched  summer  leaves,  in  the  yet  maintaining  late  spring  stem,  which  i s  normally  except  near  the  flowering  roots rosette  the  the  the  of 60  top,  cluster  the cm  where in  June  July. An  important  variation factors the  and  Australia  distribution  life-cycle  through  grow,  high  axillary and  1874,  confirmed.  dormant  During  low-profile  next -  to  the  small  leaves.  continues a  North  although  Wood a r e  rosette  and  and  in  History  There  seeds  Zealand  world  South^Africa, and  Mew  Africa,  Schraidl's  Harper  Life  South  Wood  jacobaea  listed  a  1880-s,  (Harper §•  w  in  the  influencing  section  headed  point  to  stress  life-cycle plant  size  Plant  stages w i l l  be  Habitats.  is and  the in  covered An  considerable plant  size.  The  more  f u l l y  in  i l l u s t r a t i o n  of  the  15  v a r i a b i l i t y (1935):  in  seed  plant;  at  seed  production  Hedmenham,  plant.  Rosettes  crowns  of  the  occasions f i r s t  summer.  plants  with  Defoliated as  Plant  of  done,  unlikely  that  i s , in  particularly  of  the  occupies.  This  in dune the  community  that in  on  his  rosette  a  stem  and stage  plants are  plants  may  174,000  per  from  flowers  Cairns  1940) ,  persist  usually  also the  per  plants.  common  after  or  the  root  On  rare  in  their  but  if  through  the  single-stemmed,  in  some  produce main  data  4,800  and  may  are  stems  Senecio  which  the  i t s  f i e l d  between  section  a  areas.  seed  seeding  crop  as  period.  (J.L.Harper,  jacobaea  most  for  this  Yet  the  plant  the  man's  .  the  Later  Tyria S.  pattern  salient  probably  pers.comm.)  and that  the  in  work  a c t i v i t i e s .  describes and  evolved  following  community  lands, is  S.  land.  range  agricultural  that  jacobaea  agricultural  natural  agricultural  plant  averaged  flowering  Poole  months  extending  interactions  aware  four  community  successful  the  the  averaged  fragments,  produce  1935;  damaged to  root  i t  Cameron's  Habitats  is  plant  from  may  from  Henley-on-Thames  Although  or  shown  summer's  multiple  three  It  grow  damaged  i s  Buckinghamshire,  (Cameron  are  at  previous  second  late  may  rosettes  summer  rosettes  production  the thesis is  features natural  was  highly  a c t i v i t i e s , to we  jacobaea of  type  evaluate must  be  normally  establishment of  the  sand-  habitat  of  16  1  In  countries  habitats as  in  and  i t  occupies  British in  as on  are  Columbia.  southern  extends occurs  where  far  S.  jacobaea  usually Here  i t  as  the  overgrazed  or  cleared  been  associated is  agricultural  north  has  common  areas  of  with  in  the  agriculture,  the  Fraser  Vancouver  Comox-Courtenay areas,  introduced,  Valley  Island.  area.  It  Usually  right-of-ways,  i t  and  road  embankments. The lands  in  f a i r l y Bay  pattern New  Zealand  t y p i c a l .  of  (Alio  of  f e r t i l i t y  summers f e r t i l i t y  (Rankin  1960;  sward  kept  (Glue is  a  1957).  and  is  Cairns  in  to  be  f e r t i l i t y ,  i n i t i a l then the It  S.  burning  pasture  a  and  to  newly  problem 1962),  i s  i f  adjacent  failure  of  the  competition  with  and  dry  spread  s o i l s  on  or  grasses  fern  in  dry  l i g h t,  low(Alio  dairy  farms  are  these  seeds  and  pastures  up  absent  pastures  the  country  f e r t i l e  the  of  opened  under  of  became  into  developed  rare  probably  rapidly  flourish  plant of  agricultural  clearing  was  on  i t  i n a b i l i t y  to  cover  even  the  sandy,  continued  in  over  jacobaea  continues  Dingwall  of  jacobaea  i l l u s t r a t i o n ,  Island,  also  The  S.  the  infested conditions  to  (Cameron  when  establish 1935;  Poole  1940).  Although tends  low  It  closed,  of  useful  particularly  consequence  themselves  the  1967).  i t  a  the  where  s o i l s ,  While  is  is  1959).  (Coles  spread  North  after  scrub  1959).  In  Plenty,  established  low  of  the  absent  plant where  can the  tolerate water  a  range  table  i s  of  soil  high,  or  types, where  i t the  17  s o i l  is  maintained  It  i s  abundant  or  absent,  tolerate plants 5.0.  as  Weeting  flowering  stem  s o i l s  150-180  cm  The low basic  which  1  dunes.  i s  as  a  have  and  Cairns  the an  of  a  study  on  Hepburn  English  dunes,  inhabitant  the  into  h i l l s  In  an  England,  from  early  Salisbury  i n i t i a l l y years,  "a  and  of  mass  acidic  after  more  sparse, plant  to  size  of  was a  4.5  single  whereas  stems,  to  and  on  may  be  jacobaea  the  plant  richly  carbonated,  habitats  of  the  communities of  described that  sand Senecio  sand  1952).  are  yellow  of  l i s t  young  Salisbury  -  »late  development  species  1952;  establishment  dunes  Hepburn,  i t  as  "an  almost  when  in  bloom  turned  gold".  the  sand-dune  showed  =8.2),  that  became  another  acidic  pH  1971),  exposed  dunes",  on  (1925) (pH  to  of  work  alkaline  alkaline  sand  small  s o i l  drained,  in  basophilous  the  produced  conditions  stage  1932;  universal  S.  open,  sand-dune  common  or  of  1957),  1940).  with  specialized  early  two  well  and  the  Wood  becomes  the  (Dempster  associated  s o i l s ,  (Braun-Blanquet in  high  l i g h t ,  and  usually  often  (Poole  where  Heath  and  i n a b i l i t y  explain  England,  plants  Studies  jacobaea  part,  (Harper  soils,  The  cm  neutral to  in  Weeting  f e r t i l i t y ,  adaptations dune  may,  conditions  or  decreases.  30-45  high  s o i l  capacity  calcareous  Heath,  at  richer  pH  s o i l s  Plants  f i e l d  l i g h t ,  s o i l  acid  at  on  near  the  neutral  hundred  conditions  s o i l s  of  Southport,  dune after  years.  occurred  s o i l  was  one  hundred  Similar  changes  on  the  dunes  of  18  Lake  Michigan  this  is  have  been  a  continual  (Braun-Blanquet general  phenomenon,  studied  (Chapman  decrease  in  organic  §•  was,  according  was  fourteen  ridge  that  twenty-five §•  jacobaea  not  of  w i l l  dune,  so  found  to  European  addition  to  the  can  be  quite  unstable  the  protection  many  plants  rhizomes  (e.g.  convolvulus) , (sand (sea  sedge), wheat  systems,  by  sand  Ononis C.  incurya Most  dominated  vertical  to  by  rely  horizontal,  the fixed  expanse Europe  by  plants  the  dunes.)  yellow in  dunes  spite  of  consequence  producing  horizontal  soIdane11a  (rest-harrow) ,  plants  is  a  Calysteqia  sedge),  dune,  British  As  i t  descriptions  s h i f t ,  grass.  when  but  in  a  ridge  specialized'  mentioned, to  on  text  large  following  marram  (dune  and  the  other  continues  system,  through  grey  usually  covering  dune  dune,  particularly  the  rep_ens  proceeds  of  and  dune  ridges,  a  steadily  another  because  (The  Ammophila,  grass). both  to  ridges.  already  sand  offered  react  older  is  a  the  on  arenaria)  as  from dune  dunes,  and  on  that  found  conspicuous  and  yellow  that  dunes  also  older  named  factors  those  the  dune,  likely  Southport  clear  elsewhere.  refer  on  content  uninterrupted,  embryo  is  Salisbury  o l d ,  not  from  i f  least  the  years i s  i t  Salisbury,  present  (Aramop_hila  rarely  In  to  uncolonized sand,  grass  are  being  yellow  s t i l l  that  as  stages:  The  marram  It  development,  following dune.  old.  and  carbonate  content.  disappeared  mentioned Dune  In  years  at  1964).  calcium  increasing 3§£2£S®§  1932),  and on to  Car ex Aqropyron  (sea arenaria junceum  extensive hold  the  plant  root in  19  the  s o i l  and  reach  water  in  dry  summers.  Glamorgan  contained  25  species  in  with  of  the  height,  5-33%  of  The  plants,  ground  yellow averaging  remaining  dune  at  70-80  cm  bare  (Duffey  in  damper  1968) . Yellow spring  months,  fruited this one  dune  of  sand  and  the  most  the  early  wetter  months  of  early  the  In  specialized yellow there  is  were  so a  (wood  groundsel)  (Salisbury  dune  habitat  described exhibit  (for  Senecio  the  In  jacobaea  is  early  rate  of  seedlings. with  root-system the  and  1952).  the  rapidity  enduring  the  which  and  earlier  for the  grey  the  have  continuous  dry  which  during  the  conditions  dune,  pioneer  species  considerably vegetation  /  the  the  highly of  the  diminished, cover.  and  Senecio  genus  is  represented  by  S.  and  S.  yiscosus  (sticky  1952) .  jacobaea i s  of  for  flowered  providing  "the  groundsel) ,  i t  some  that  the  (Salisbury  habitat,  phase,  disappeared,  S.  summer  extensive  suited)  SY-iiaticus  Although  of  have  overwhelm  plant  dune  conditions  has  actively  annuals  arrive,  not  an  grow  phases."  usually  jacobaea  to  noted  this  next  dune  the days  does  develop f i t s  to  specialized  p.232)  dune  the  of  biennials  (1952,  seedlings  tend  dry  rather  accumulation  Salisbury the  and  before  harsh  plants  appears  found New  in  to  other  Zealand.  features  be  of  adapted  habitats,  These the  primarily  dune  such  habitats  to  a  as  I  usually  communities  where  f  ragwort §*  flourishes.  d§cobaea  in  Perthshire, slopes. found of  in  one  and  Tyria  "marked  the  larvae  heavy  in  Meadow,  disappeared (1952)  disappear In  1949  sheep  in  populations  an  a  been  series  Islands, stages  was  in  replaced (mostly  important  by  S. to  in  and 1948.  infested"  growths  of  1957).  jacobaea  to  jacobaea  had Holly  may  with  due  S.  1955  any  jacobaea  probably  in  in  year",  p l e n t i f u l  Wood S.  year  was  factor  plants  Islands  present  and  of  "heavily  Dense  of  steep  had  of  pressure  from  were  were  one  plant  being  1948.  In  permanence  decline  (Harper  almost et  a l .  virtually  winter.  terminology  given  the  after  1949  jacobaea  and  decreased.  abundance  that  1956  The  discussed  plants  the  Oxford,  that  c l a s s i f i e d  herbivores  by  during  the  in  in  and  intermediate  Pembrokeshire  changes  1947,  by  noted  the  Argyll  rocks  S.  grazing  was  (1954)  flowering  grazing  Port  either  in  found  Pembrokeshire in  communities.  jacobaea,  On  the  jacobaea  exposure,  S.  disappeared  Although  S.  that  woodlands.  of  (1962)  woodlands  calcareous  wrote  ecology  Gillham  of  of  forest  as  of  location.  underwent  (1957)  found  degree  biology  almost  the  Ratcliffe  deciduous  areas  beech  competition  Goodman the  in  grassland  or  and  mixed  Wood  on  (1955)  sheep),  be  and  immature  developing  in  two  publications  through  Mcvean  Scotland,  Harper  Gillham  in  20  as  a  that  of  Southwood  'temporary it  (1962),  habitat'  undergoes  such  for  S.  jacobaea  would  species-specific  erratic  fluctuations  21  in  abundance  stage in to  in  and  sand  dunes.  abundance  refer  S.  jacobaea's  references need  for  behave  on  that  Economic  fluctuations studies  First,  i t  may  the  in  grass.  l o w - f e r t i l i t y " . . . i t  their  to  in  shows  species  off  habitat  references to  to  grassland  sudden  dunes.  in  dune  communities  i f  and  populations grassland  for  of  The  and  not  absence  of  points  of  S.  out  a  jacobaea  habitats.  Gillham's  serai, changes  habitats  sand  evidence  cycles  intermediate  -  see  dune  jacobaea  reasons.  wrote  the  an  There  claim  is  (1955)  abundance.  Importance  Senecio  area  occupies  exclusively  published  plant  plant  However,  differently  the  the  prime  further  insufficient  two  that  may  as  take  become  an  efficient  over  pasture  Describing  pastures was  not  properties  in  S.  a  serious and  land  and  New  uncommon  for  because  they  problem  competitive  jacobaea  northern  weed  pioneer  drastically  as  for  reduce  the  worst  Zealand,  Alio  (1959)  to  forced  dairy-farmers could  not  weed  be  control  of  the  ragwort." Secondly, densities  S.  because  horses,  and  due  alkaloids  of  to S.  to  jacobaea  cirrhosis  of  i  a  jacobaea of  the  lesser in  they the  the may,  liver  can  toxic  effects  extent,  sheep.  plant. over and  be  If a  die.  a  problem of  the  The  cattle  at  much  plant  toxic  on  cattle,  effects  and  horses  period  of  months,  Harper  and  Wood  lower  eat  (1957)  are a  lot  develop cited  22  references  to  the  occurrence  and  characteristics  of  the  disease. The  seriousness  prompted in  research  several  of  into  countries.  In  New  established  control  the  Given  (1965)  jacobaea  had  thought  that  been  much  waste  In  Victoria,  of  annually  (Schmidl  these,  jacobaeae  In  of  the  Canada  control  never  Huffaker  program  in  methods was  exerted  much  1959).  and  has  moth  control  f a i l u r e " ,  into  does 1972  introductions have  died  success.  Nova  Hence  of  Senecio  Glue  (1957)  New  Zealand  had  Abbotsford,  B.C.  In  considerably was  Nova  million  including  l i t t l e a).  the  the  are  spraying  than  prevent  introductions  last  seed  dollars  aerial  more  Several  over  of  control  forty  f l y ,  methods  Introductions Prince  B.C., Scotia  reduced  a  of  years,  Pe^ohylemyia  out.  Scotia,  Nanaimo,  half  Victoria  biological  in  over  measures,  (Schmidl  more  colony  but  in  areas  cinnabar  biological  spraying  this  and  Nanaimo  areas,  that  "complete  Brunswick,  has  the  comm.  a  control  (Hardy),  established  write  made  and  considerably  (Miller,  although  been  some  agricultural  biological  Zealand  Australia,  spreading  have  in  and  in  time".  on  1964) ,  further  but  been  "a  spent  Tyria  plant  could  problem  chemical  successfully over  the  with the  plant  established  at  of  Tyri.a  Edward a  density Chase  met have  with become  Island,  smaller  resulting  the  have  population  larval (Harris  River  New  buildup  1972).  site  at  in  The 1964  23  (Wilkinson  1965),  effectiveness desired in  the  success of  of  threshold original  Releases  (Hawkes  and  supplementary  i t  the  is  level,  Tyria 1968),  too  insect  release  of  establishing  (Heade)  and  to  although  to  assess  control plant  the  the  size  long-term  weed  has  below  been  the  reduced  area. in  the  and  western  additional  the  seed  a  flea-beetle  control  early  f l y  agents  Hylemya  USA  also  research  give has  (Pejjohylemyia)  Longitarsus  (Frick  1969,  1970).  promise the  of  purpose  seneciella  jacobaeae  as  2U  THE  STUDY  AREAS  Most Garner  of  the  Ranch,  Island  (Pig.  here:  a  f i e l d which  1).  One  grassy  conducted  a  of  were  w i l l  described  be  The  Garner  as  and  being  study  Ranch  "outside  stands  of  variety  of  The  8  once  is  midway 1).  consists  as  grazing,  and  confined  to  small  areas  Figure  and  are  follows.  2,  Richard elevation is  a  of  l i e s  about  22  and  Top  The  exceptions  being  Lake  Field  dominant a  and  narrow some  between  I  in  a  of  i s  is  be  described where  jacobaea.  l o c a l l y i t  of  the  land  above a  these  sea a  rock  is  poorly  are  shown  bluff  s o i l  at  Power  outcrop  drained  for  a  livestock  basin  brown  brown  amongst  necessarily  level.  steep  group  concretionary  was  to River  used  subdivision,  mean  Chase  Chase  being  sloping  and  referred  pasture  ranch;  I  Other  trips  townships  i s  the  Vancouver  sampling  c a l l  gently  of  on  B.C.,  my r e s e a r c h  the  s o i l  on  the  and  urban  above  band  on  also  cleared  above  area  i t  shall  Hence on  metres  sloping  elevation.  Richard  as  Lake  s l i g h t l y  elevation,  production.  Hanaimo  Senecio  twice  timber,  such  done  w i l l  on  Since  River"  of  was  Clearbrook,  or  d e t a i l .  second-growth  hay  study  south  near  in  Chase  purposes,  km  experiments  (Fig.  ranch  this  l o c a l i t y  visited  Extension  area.  for  h i l l s i d e  series  not  is other  l o c a l i t i e s  River  work  30 m  ' 90  podzolic, peat in  the  an Pylon  at  at  in  m the  around Power  25  FIGUBE  1  L o c a t i o n map Clearbrook.  of  the  study  areas  at  Chase  River  and  25 a  26  FIGURE  2  Map of the Chase R i v e r study area showing the main l o c a t i o n s . The s q u a r e s down t h e l e f t side indicate the p o s i t i o n s of pylons carrying transmission l i n e s .  i  26  27  TABLE Weather Airport  1  data for Nanaimo (in parentheses).  Bean  Monthly  Airport  and  Temperatures  Abbotsford  (C)  Year  April  May  June  July  Aug  Sept  1969  8  13  18  17  16  14  1970  8 (7)  11 (11)  17 (16)  17 (17)  17 (17)  13 (13)  1971  8 (8)  13 (12)  13 (13)  18 (17)  19 (18)  13 (13)  1972  6  13  14  18  18  13  Monthly Year  April  1969  112  1970  Precipitation  (mm)  June  July  25  41  10  81 (163)  36 (48)  25 (36)  28 (64)  13 (5)  51 (112)  1971  38 (69)  28 (69)  56 (142)  23 (33)  13 (20)  56 (114)  1972  89  25  56  May  8  48  Aug 25  Sept 86  67  28  Pylon  area.  The s o i l  loam  to  s i l t y  Fig.  2  consist  well  drained.  is  almost The  clay  leafed  f i r  the  study  (Ribes  grape  yesca  var.  thistle (Prunella  over  Willow  vulgaris)  as  of  s i l t  sites  sites;  in to  Lakeside  and  i s  stump  high  jacobaea  i s  wild  burned piles  Field,  including  everlasting  stumps are  that  also  Oregon  (Fragaria  aryense),  i n  bull  self-heal (M^£llSli§  and around are  areas  a  aquilinum),  spp.),  occur  currant where  strawberry  (Plantaqo  plants  within  and r e d  (Cirsium  stands  and b i g -  scattered  Top  as  (Tsuga  smaller  (Pteridium  t h i s t l e  such  menziesii),  present  pearly  partially  in  also  bracken  these  while  found  on  trees  hemlock  scouleriana)  plantain  of  These  are  muniturn),  the  scattered  where  Senecio  "density.  scattered  some  local  areas  i t s  years  of  study.  One o f  the  the  as  moderately  timber  (Arbutus  shrubs  Canada  ,  Many  appears  Senecio  of  plicata),  (Salix  plants  yulgare),  Top F i e l d .  jacobaea  occur  bracteata),  piles  soils,  menziesii),  aguif2li.u§)>  ^i^aSfii^SSa)* numerous  loam  second-growth  arbutus  (Polystichum  (C.  classified  designated  stoniest  gacrgghyllum)  smaller  fern  i s  other  sandy  (Thuja  rubra),  (Acer  (Mahonia  sword  Pylon  the  the  are  and cedar  area.  of  i s  trees  sanguineum)  variety  a l l  (Pseudgtsuga  (Alnus  maple  Power  free.  dominant  alder  at  gravelly  Top F i e l d  heterophylla), of  loam;  of  stone  Douglas  type  density  over  the  varied  the densest  study  area,  noticeably  infestations  and  during  in the  was on T o p  29  Field in  where the  jacobaea  mid-1960's  (Wilkinson and  S.  when  1965).  By  1972  covered  much  less  of  Cattle  were  pastured  times  during  each  area  than  grasses  are  orchard  tenuis,  while  also  present.  the  in  conditions  during  grassy  h i l l s i d e about  76  metres.  to  loam  (Soil  data  for  site.  There  clump  of  dominant  Hap  they  4  On  fescue  (Festuca  velvet  grass  are  (Holeus odpratum)  present.  The  there  were  smaller  area  slope  1964).  cover,  high  at  t i c k l e  (Fig.  1  common Agrostis  re pens  average  m  x  are are  weather  is  2  elevation as  only of  s i l t  some  the  loam weather study  a  small  slope.  The  scabra),  red  re gens) ,  vernal  (Dactylis  is  the  by  (Agropyjcon  Rhytidiadelphus  of  The  km f r o m  although  m,  Trans-Canada  (Agrostis  grass  40  the  gives  crest  grass  orchard  the  Airport  given  broken  the  lanatus),  1).  was  Table  grass  twitch  100  beside  which  grass  T.  Nanaimo of  the and  and  in  study.  an  Vancouver  different  heavily areas  _gra t e n s e  the  at  glomerata)  from  is  10°  moss  acres)  released  more  indication  of  site  and  (17.5  Field  pasture  c l a s s i f i c a t i o n  rubra) ,  ha  sites  fed  the  an  Airport,  m  Top  the  (Dactylis  Matsgui  complete  grasses  also  of  7  f i r s t  on  of  Trifolium  a  km f r o m  texture  trees  (Anthoxanthum  most  as  study  Abbotsford is  on  summers  with  80  Soil  1  the  ground.  grass  the  Clearbrook  Highway,  plants  elsewhere.  Table  of  was  Climatological data  presented  The  the the  clovers  most  Tyria  summer;  Lakeside  are  covered  and  grass  glomerata)  triguetrus  and  the  30  common  horsetail  Other  herbs  daisy  was  western  (Prunella  f i e l d  the  present  (Chrysanthemum  aryense), heal  (Eguisetum  chickweed  vulgaris),  largest  plants  unfenced riders.  and  red  (Cerastium  open  to  occurs  the some  {  Plantago  Canada  (Ranunculus clover  also  widespread. spp.) ,  thistle  oxeye  (Cirsium  occidentalis),  (Trifolium  self-  ££ a t e n s e ) ,  and  aryense).  measuring  during  are  plantains  buttercup  jacobaea  grazed  were  leucanthemum),  Senecio  not  aryense)  over from  period  most  of  1-1.5  the m in  1968-1972,  disturbance  by  h i l l s i d e , height.  The  although  pedestrians  with  and  i t  area is horse  31  PART  I.  RESPONSE  OF  SENECIO  JACOBAEA  TO - D E F O L I A T I O N  INTRODUCTION Many features often  as  that  S.  u t i l i z e  secondary  anti-herbivore  does,  clear Has  plants  defoliate  any  such  jacobaea  adaptations.  large  areas  adaptations  evolved  substances  of  are  any  Since  can,  and  jacobaea,  ineffective or  structural  Tyria  Senecio  physical  or  against  i t  is  Tyria.  chemical  defence  mechanisms?  It  appears  sparse  hairs  on  to the  even  the  youngest  for  f i r s t - i n s t a r  establish  a  effective §•  that  (Merz  (1959)  i n h i b i t s as  were  been  in  extracted  concentrations alkaloids  of  by  chemical  Tyria  given  A closely  activity  by  not  essential larva  related  and  Raven  on  lack  species,  densely  feeding  can  packed  the  leaves  (1964)).  acceptable  When Senecio  larvae. against  Several  Aplin  including  some  some  herbivores  are  alkaloids  have  hepatotoxic  jacobaea; by  few  species  from  of  The  single  from  leaves  defences  S.  a  is  Senecio  substance  Ehrlich  Tyria  jacobaea.  Senecio,  of  feeding  and  a l l  Tyria.  deterrents.  feeding  II),  Not  substance, by  hinder  Group  glandular  reported  are  not  (Part  larvae  from  physical  larvae.  site.  a  refused  S.  do  against  this  Effective  any  larvae  exudes  with  present  Tyria  deterrents  hairs  species  leaves  feeding  vulgaris,  painted  lack  their and  structure  Rothschild  found  in  S.  and  (1972).  The  jacobaea,  are  32  reviewed  by  Aplin alkaloid year, to  plant  also  of  in  Senecio  unlikely  S. S.  is by  The  a  Rothschild  alkaloids  in  Since by to  the the  does  Tyria  plant's severe  Tyria  the  over  are of  basis  the  one  not  S.  presence  of  to  a l l  1950). Jacobine  (=jacodine) and  1960).  alkaloids  the  from  thousand-plus  species-specific.  (Leonard  the  in  (Leonard  vulgaris,  each  varying  widespread  alkaloids  response  in  However,  defoliation  damage  affect  its  occurs  senecionine It  is  highly  in  Senecio  selective  pressure  that  mechanisms  by  i  Tyria,  are  mechanisms.  able  to  store  selectively  stores  s  comment precise  that role  i t  is  of  the  Tyria.  overcome  wonders  imposed the  i t  the of  defence  Tyria  authors  evaluate  one  deterring own  particular  successfully  alkaloids  than  in  found  these  to  defence has  rather  insect  (1972)  present the  considerably  weight  most  species  the  alkaloids;  at  of  seneciphylline  including  alkaloids,  Aplin  d i f f i c u l t  proportions  alone.  by  seneciophylline.  and  cineraria,  used  toxic  varied  Alkaloids  are  that  the  dry  jacobaea  probably  the  a  toxic  direct  Tyria  on  1960),  Senecio  Senecio  and  jacobaea  year.  species  11  that  contain  therefore,  jacobaea exerted  a  (Mothes  in  in  S.  found  proportion  Senecio  occurs  occurs  in  within  found  13  Rothschild  t o t a l  groups  Those  (1970).  occurring  0.79  species  in  and  the  0.25  Warren  how  the S.  Tyria.  persistence  of  problems  jacobaea To local  what  posed  responds extent  populations  33  of  S.  jacobaea,  habitats? work  This  designed Other  to  to  of  a  1935;  affected  by  unaffected  is  more  S.  work  agent  are from  addition  jacobaea  growth  to  period  with  to  the  an  and  Poole  not  Tyria.  the  the  to  effects  doing  the  flowering  in  1940).  studied  and  problem  f i e l d  by  plant  of  I  peaking  by  plants  with  control  adequate  control  results  Tyria  as  a  of  that  work  the  the of  the  some  biological  1968).  on  were dying,  However,  an  of  perennial  (Hawkes  studied of  practical  becoming  competition  Tyjria  jacobaea  plants  ways:  The of  experimental  the  new  response  compared of  interest.  S.  When  by  Cairns  synchrony  and  to  of  the  the  three or  of  towards  se.  effectiveness  defoliation,  determine  p_er  crop,  The  confounded  disperse results  response  towards  responded  academic on  the  not  and  to  presents  orientation  seed  were  plant  questions.  damage  they  the  thesis  examined  with  by  of  these  second  than  separated  In  at  Tyria  Tyria  plants  be  but  damaged  (Cameron  control  of  have  to  producing  important  a b i l i t y  control,  jacobaea  of  look  workers  mechanically by  the  section  defoliation,  problem S.  or  cannot  response  pattern  of  main  larval  plant  biomass.  of  summer feeding  34  METHODS  Summer The Chase  Growth study  River,  intervals. sample near faced were I  In  lake  leaf old, be  sampling  and  noted flowers  on  I  2).  The  of  the  proportions each  Defoliation  :  leaves, 5  in  for  second  measuring  every  leaf,  the  length  i t s e l f . of  f i r s t of  For  closed  the the  buds,  nine  and  weeks,  week. lamina last open  were  proved  and I  maximum as  leaf  and  (ground  excluded,  every  f i e l d  area,  height  Measuring  after  a  sunlight,  the  length,  cm w e r e  regular  in  f u l l  plant  leaf  at  representative  in  Weekly,  made  at  plants  Tyria.  length:  lamina  were  measurements  adopted  leaf  second-year  was  data  a  from  than  I  selected  grazed  shorter  as  record  cattle  Leaves  accurate  plants  since  of  leaves.  to  plants  number  for  the  1970  following  method  length  of  bud),  as  measures  convenient  protected  yellowing  almost  second-year  was  competition  the  width.  in  single-stemmed,  well  apical  it  (Fig.  l i t t l e f a i r l y  growth  mid-May  20  recorded  to  where  of  the  of  was  the  recorded plus  four buds,  to  two  petiole, weeks  and  I  mature  plant.  Experiments /  Experiments defoliation were  not  were done  to  determine  conducted at  Chase  at  the  River  the  plant  Clearbrook for  the  response  study  area.  following  to These  reason.  35  Finding, area a  or  where  maintaining, extensive  d i f f i c u l t  controls  in  problems  within  prospect.  one  was  stand  Senecio  area  To  Any  such  two  mimic  feeding  pressure  by  heavy  structures larvae the  sliced  off  leaves, The  leaves  plant's  B  fed  on  soft at  the  plant.  petiole  a  were  would  growing  the  when  I  could  be  These of  portion  plants,  development, were  measured, dry  weight  experiments and as  I  B(Biennial) second-year  been  to  not  work  attack an a  be  by area  large  subjected  stands  in  sure  of  to the the  summers.  I  removed  i f  an  excessive  included  flowers,  stems.  in of  then  the the  a l l  Leaves  case  of  petiole  was  oven-dried  with  determinations.  selected  designated  making  needed  apical  wedge-shaped  for  I  consumed  portions  was Tyria  Tyria  except  counted,  thus  consecutive  base  defoliation  plants  where  that  inflorescences  the  crown  plants.  years.  required  single-stemmed root  not  the  and  For  had  farms  additional  contained  that  for  buds,  the  some  and  cooperation  of  l e f t .  for  simulate  attack  jacobaea  the  solution  on  number  lower  Tyria  establishing  changes,  Consequently  an be  introduced  to  in to  have  were  plant  were  from  appeared  hand,  and  myself.  controls  other  habitat  area  as  occurring  compromise  small  plants  protected  Nanaimo  the  the  would  My  plants  was  the  with  d i f f i c u l t .  measures  owner's  area  uniform,  of  control  On  associated  defoliating that  defoliation  another  comparisons  undefoliated  a  total  them  on  the  plants,  or  P  plants  that  of  basis  120 of  (Perennial) had  just  36  developed The  root  from  rosettes  crowns  of  grown  in  previous  tended  to  have  describe  and  perennial The  plants of  to  1966).  Therefore  at  random  after  a  plants  in  September  the  marked  of as  used  the  plotted  on  a  in  the  root  crown.  stalks  had  perennial,  grouping  enabled  in  and  me  biennial  to and  as  was  B  free  the  the  the  The  of  respond  defoliation (Bornemissza  for  when  after  A l l  amount  public  15  defoliation  Tyria  P  normally  The  and  access  to  as  possible  of  the  stem.  weeks B  the  area a  Their  the  1971  were  shoot  with  Nonetheless  plants  plants  survey  map.  Results  15  new  a  chosen  three  persistence  by  were  This  the  of  plants  procedure.  remaining  assessed  appropriate  time  chosen  above  plants  recorded.  before  to  summer  controls.  base  the  plants'and  by  was  at  River.  weeks.  large-scale  'disappear'  handled  15  inconspicuously  around  were  defoliation  dates  the  Chase  when  summer  collar  to  of  different  1970,  following  to  single  flowering  This  a b i l i t y  three  1970,  three  production  Because  at  30  were  crowns.  plant's  defoliated  further  P  leaf  7,  with  the  plants  development  the  plants  and  repeated  the  period  June  by  that  the  response  plant  affect  defoliated  showed  i.e.,  root  the  judged  separately.  appears  On  years,  study  the  plants  larger  stage  covered  P  as  a  again  and  15  examined  growth  and  plants  into  in  June  1 9 7 1.  the  plants  were  plastic  numbered  position  was  few  assessment. section.  of  was  plants This  also  seemed  problem  is  37  Secondary How growth  Seed  much  seed  after  and  in  new  plant from of  the  each  closest these  seeds  and  jacobaea  per  55  non-defoliated  on  a  l e f t at  Normal near  a  of  to  1971,  quadrat.  2  the the  each  From  number  in  from  the  a  of  number  of the  quadrat,  determine  was  of  September  and  production  Lakeside  I  capitula.  corner  seed  production  line  on  stem,  secondary  ran  1 m  made  few  random  seed  plants  m in  the  from  during  were  removed  capitula  plants  10  notes  lower  capitulum.  the  F i e l d ,  every  I  the  compare  Top  plants  plant.  produce  defoliated  location  to  chose  To  in  plants  their  on  S.  naturally  defoliated  shoots,  capitula  and  Lakeside  sampled  completely  can  defoliation?  non-defoliated transects  Production  and  number  stand  estimated  in  a  data  the  of l i k e  manner.  Changes I and §•  in  used  Form  two  and  sampling  distribution JSSSfiasa  chemical and  in  River the  a  a  or  a  3  -  been  number  of  growing  from  each  root  way,  along  f i e l d  per  crown.  roughly  the  The  a  gather  in  for  control  sampled  plants  to  plants  ungrazed I  methods  of  b i o l o g i c a l  small  area  Distribution  several -  in  along  and  33 the  Clearbrook  same  the  transect  areas.  years  m x  road 1  line,  the  m wide,  number area  study  to  of  was in  any area Chase  recording  stems  growing  sampled  1970  form Where  without  Clearbrook  the  transect  meter  different  on  and  this  1972.  38  The came  contrast  from  plants  samples  had  Bragg,  been  the  defoliated sampled  where three  p a r a l l e l  50  transects  greater  of  River egg  concern  laid  out  numbers  were  quadrat.  Because  from  each  size  from  Pylon  are 4.  100%  between  Site  2 lagged  at on  in  to  The  was I  recording  m . 2  i t  The  Table  of  defoliation  about  1971, a  great  from  3 and  year.  are at  The  Two  above  again  I and  the  site  sampled  for  pairs  to  of  of  each  information the  quadrat  at  Power  separately  1 rose  from  defoliation  Chase  random of  sites  presented  my  stakes  of  reduce  two  an  reflected  lines  deal  Site  whereas  I  been  when  coordinates  necessary  in  had  1968)  method  and  the  data  Fort  primarily  the  axes  a  years.  through  1972  guadrats.  as  where  transects.  and  the  areas  described  collected  determine  1968 and by  were  found  0.5  amount  of  in  50%  to  plants  River  samples  placed  1  at  were  1971.  Plants  were  Clearbrook  on  June  I  as  In  same  jacobaea  C a l i f o r n i a ,  (Hawkes  data  1959.  the  angles  to  combined  Table  taken  right  some  m transects  in  randomize  plant 2  1  roughly data  used  1 m  years  recorded m x  in  S.  River;  for  Tyria  distribution,  to  at  of  growing  Chase  annually  released  along  freely  and  successive I  was  of  Bragg  site  1970.  Chase  areas  Fort  release  in  Tyria  analysis  at  several  three  The  were  for  these  defoliated  main  i t  sampled  to  29,  collected July  1972;  from  6,  1972  I  used  and  randomly from  them  to  Williams  m  z  Farm  determine  the  quadrats (Fig.  1)  biomass  39  relationships plants.  of  rosettes,  Unfortunately  carried  out  done  plants  to  at  that by  a  single-stemmed,  similar  time  at  Tyria  sampling  Chase  River  and  multi-stemmed  routine  because  could  of  not  the  be  damage  larvae.  RESULTS  Pattern The eaten  by  Tyria  3  some  light 17  plants, of  Plants although stopped  over  the  the  seeds  in  larvae I  rate  of  in  in two  June  respectively.  20  the  selected  from  remaining  on  the  17  those  plants  distant plants.  inflorescences  increase July.  flowering weeks  3-4  and  throughout  late  of  the  This  plants,  only  the  moved  discarded  taller  disperse.  grew  had  by  maximum a s  Clearbrook  plants rate  i t s  that  of  data  in  the  the  summer  were  plants. There  of  was  three  of  calculation  inflorescences.  study  f i n a l  three  from  grew  advanced  of  data  so  the  the the  reaches the  larvae  feeding  biomass  Growth  leaves  summarizes  these  most  Summer  upper  Fig.  of  of  cm  July  The  seeds  where  four  both  was  plants  less  than  suggesting mature,  consistent  during had  height  showed  July,  is  in  with  averaged  28  that  3a),  when  were  average plant  measurements and  whereas cm a n d  32  the  height before from  perennial their cm  per  I  growth  probably  biennial(B)  august,  slowing  that  and  (Fig.  (P)  growth month  40  Although multiple include  plant  the  the  leaf  dry  estimating S.  at  averaged plants. plant  my c a l c u l a t i o n s  weights  of  leaves  One  biomass  was  in  average,  11  leaves  fewer  fact,  did  peaking  of  The  larger,  death by  lower  lamina  residual  the  Leaf plus  to  use  of  was and  the  production  in  measures,  was (Fig.  area  both  3).  This  drop  through  leaves,  were  being  leaves  before  the  the  length petiole.  4).  leaf  leaves  loss refers Both  The of to  the  the  by  gave  rapid total  the  leaf  the  period  length  on  considerably  added  lamina  any  cumulative  while  leaves  and  the  the  of  River  both  by  caused  flowering  B yet  by  senescence,  larger  measures  July,  to  the  alone.  While  sum  form  count  count  July,  was  when  Chase  square  dropped  cumulative the  mean  followed  during  (Fig.  did  early  on  t a l l e r ,  leaf  leaf  unchanged  Schmidl(1972a).  sensitive  length.  the  inflorescences  lower  smaller of  reduce  used  growth  cm  on  not  I  example,  than  weight  leaf  month  12  plant,  did  height  the  For  dry  over  length  this  noted more  leaf  the  per  in  of  biomass  leaves  of  much  not  quantity  and  on  regression  number  new,  variance  were,  of  the  marked  in  regressed  omitting  Clearbrook  development  of  the  my  I  biomass.  inflorescences  for  height  biomass  of  habitats.  numerical  during  and  reason  plant  estimate  in  height  for  to  used  different  In  The  (1971)  equations  count.  appreciable  sums  Meijden  height  jacobaea  plants  der  regression  only  of  van  leaf than  some count.  is  also  area was  alone,  similar  loss  was leaf  not  to  results,  FIGURE  3  Growth of Senecio jacobaea flowering the summer, 1970 (n=17). Means are standard error.  plants given  during ± one  60 w E o  35  CD > CO CD  40  CD  f  CD  X  m CO  25  20  0  1  —i  4  1  1  6  1  15  r  8  1  -i  4  1  1  1  6  8  18001  350  1600-^ E o  300  CM  £ 1400 p. CO  CD  2 1200 <  250  CO CD  CO CD  1000  200 H 800 150  —i  2  1  1  1  1  4 6 weeks  June—><  1  July  1  8  r  >  600 -June-  1—  July-  42  FIGURE  4  Seasonal change in biomass of Senecio jacobaea and the s y n c h r o n y i n development shown by f i f t h - i n s t a r larvae. Biomass data (±1 s t d . e r r o r , n=14) are from 1970, w h i l e l a r v a l d a t a a r e f r o m 1 9 6 9 . The triangle shows the date of p r o b a b l e peaking of numbers of fifth-instar larvae, corrected t o 1970 c o n d i t i o n s (see t e x t f o r details).  42a  181  43  showing  that  important The  error two  available the  v a r i a b i l i t y factor  upper  to  fraction  shown  broken  as  in  Week  is  due  5. to  heavy  The the  the  growth  of  the  standard  errors  of  leaf for  Synchrony  instar  plants  of  biomass  the  for  same  no  (Appendix  2).  The  larvae  is  shown  instars  in  the  in  Fig.  extent  interpretation  more  d i f f i c u l t  6 I  With  to  While  because  this plant  and  "available biomass  Week a  8  to  peaking  Week in  greater  increase  in  standard  the  errors  omitted  them  for  place  the  with  growth  in  c l a r i t y .  by  the  rise  mid-July,  late  f i f t h  in of  of plant f i f t h  the  peak  June.  (see  was  the  development  proportion  result  in  Growth  takes  in  9  the  increased  1.0  is  inflorescences  also  the  earlier,  estimates  9  which'  approached  of  The  Plant  an  was  leaves  the  the  the  to  synchronized  occurred  The  but  as  to  for  be  that  i t  of  from  not  not  d i f f e r e n t i a l l y  consumption  4.  to  on  biomass  Weeks  i.e.  available  notes  The  biomass  up  estimates.  Feeding  population  numbers  mean  accounts  reason,  food  i s  made  larger  the  absolute  made  biomass,  biomass  biomass  in  i s  in  of  f i f t h - i n s t a r  summer,  would  biomass.  the  referred  took  leaf  of  the  inflorescences.  the  show  in  Larval  15%  be  4  plateau  of  Over  over that  I  length  calculation  indicating  because  decline  of  magnitude  line  petiole  Fig.  w i l l  sudden  growth  the  larvae  This  The  in  biomass  inflorescences. biomass".  the  curves  Tyria of  in  in  Discussion)  studied  in  is  1970,  44  while  the  data  on  larval larval  comparison.  If  development,  i s  curve,  then  reduced  i f  The  bulk  these than  in  The  lower  the  curve  instar  Plants  of  on  densities  stripped  Field  in  plants  would  (denoted  in delay  place by  the  period  of  A.T.S.  on  Top  were  on  with of  the  same 91%  15  on  on  the 1970  triangle  June  in  higher  1969,  79%  June  29.  there 27,  of  Fig.  a  1969  (Table  1).  4).  of  shift fifth-  estimated  the  and  1970.  years  and  larval  he  the found  plants only  Assuming a  delay  larval  and  1969  would  peak  For  (unpublished),  of  1970  1970.  production.  Wilkinson in  is  in  synchrony  biomass  in  this  June.  June  both  numerical peak  and  development, the  larval  1969 and  were  in  date  defoliation  1970 in  June  for  May  Field  defoliated  on  affecting  Wilkinson  plants  the  rate  slow  within-year  interpretation  1C i n  days.  while  the  by  12  on  compared  and  improves  by  of  Nanaimo  insufficient  effect  factor  in  about  similar,  A similar  numbers July  stripped  were  main  was  at  would  which  the  major  occurs  had a  i t s  temperatures  May,  supplied  s h i f t  stripped,  increase  right,  I  for  d i f f i c u l t y  summer  in  1970  the  temperatures 2.2C  1969.  through  development  with  Top  stripped,  1969.  the  this  the  in  in  be  temperatures  kindly  percentage  were  by  1970  Data,  of  mean :  to  to  compares  feeding  suggest  assumed  larval  1970  taken  development  some  months  were  temperature,  one  of  data  have of  of  12  5%  linear  been  79%  days  over  f i f t h - i n s t a r  feeding  near  mid-  v  45  Defoliation There to  were  and  Secondary  two  distinct  defoliation;  summer, from for  which  the  counting in  bloom  of  the  I  root  the  regrowth w i l l  crown  81% of  of  amount  defoliated The  the of  for  responses  of  difference. indicates  a  plants,  f i r s t  the  P  larger a  secondary  photosynthetic  assessed  buds  growth  the  over  leaf  B  were  growth  same growth growth  September  5  were  developing  cm.  by  Flowers  similar  varied  used  were  on  most  numbers as  secondary by  P  a l l  a  of  relative  with  (Fig.  treatments.  this  2:1  5a). be  need  due  double In  a  held  different to  a  size  biomass,  which  Cairns  1940) ,  available for  and  ratio  The  greater  and  almost  of were  5,a  three  supply  less  plants  was  with  nutrient  that  time  plants  may  (Poole  the  growth  (Fig.  plants t a l l e r ,  with  summer  production  system  greater  new  Secondary in  be  plants the  than  can  the  treatment  root  in  and  summer.  stems  produced  and  plants  growth",  produced  in  was  B  flowers  of  production.  earlier  stems  and  and  of  secondary  the  consequently into  seed  of  leaves  longer  stems  secondary  P  stems  number  greater  number  of  of  the  the  comparison only  the  response  was  stems,  As  secondary  defoliation:  that  the  the  following  and  inflorescences,  b).  the  a l l  leaves  in  "secondary  plants  on  The  in  phases of  Clearbrook  remainder.  measure  c a l l  Growth  to  energy  and  direct '  from  hence  more  activity. \  While  P  plants  produced  more  stems,  and  FIGURE  5  S e c o n d a r y g r o w t h and r e g r o w t h of Senecio jacobaea plants as a function of the time of d e f o l i a t i o n . F i f t e e n p l a n t s from each c l a s s were defoliated on June 7, June 3 0 , and J u l y 2 1 , 1970. The amount o f s e c o n d a r y l e a f and stem p r o d u c t i o n i n September 1970 i s s h o w n w i t h 95% c o n f i d e n c e l i m i t s . T h e proportion w i t h r e g r o w t h one y e a r a f t e r d e f o l i a t i o n i s shown i n (c) w i t h r e s u l t s f r o m 30 u n d e f o l i a t e d p l a n t s .  46 a  P (perennial) Plants  B (biennial) Plants CO CD  c o  -t—'  CO TJ  o  c o o  10  10  =3 " D  O  CD  0-  CO  E  CD +-»  CO  c o  >. 4—' l_  CO TJ  c o o  CD  CO  o  T3 O  i_  c: co  (a)  0  o  6-  6-  4  .4-  2  CL  0  o  0.8 i  £  CO  20  20 ^  2  (b)  0  0.8"  E  CO  •+-' .  X CD  c o  0.4  a> 0.4 x:  o  CL  o  Q_  (C)  CD  0  early late mid control June July  0  early late mid control June July  Time of D e f o l i a t i o n  47  flowers plants  than  plants,  the  much  lower  than  controls.  The  size  of  though  response  the  was  B  the  response  production  of  was  of  secondary the  primary  the  the  plants  seed  seed  Chase  approximately  10%  seed  crops  defoliated at  River,  of  the  of  a  100%  reduced  to  90%  by  secondary  growth.  plants  at  produced  stems  defoliated, the  end  of  July.  exceeded, plants the  at  two  mean  whether  they  The times  at  Chase  River.  Such  l o c a l i t i e s  since  temperatures  Poole  and a  mimic  series  experiments  heights: early  in  19  33  from the  From  this  f i r s t  seed  cm  plants  cut  made  to  set  k i l l s  a  of  cut  plants  30  from  the  produced  after  the  they  of  defoliating  the  (Table  1).  responses  of  of  ground.  A l l  the  In  plants  growth, had  these  that  which  set later. 33  cutting  plants.  one  different  months  from  between  between  at  seed  near  perhaps  larvae.  secondary  concluded  percentage  be  the  or  and  few  Tyria  seven  growth  June  off  f i r s t  phrase)  secondary  experiment  pattern  they  dead" (their  is  treatments,  period  in  was  completely  Clearbrook  of  cm  being  the  to seed  of  possible  studied  the  figure  89%  agreement  and  P  production.  a l l ,  would  close  of  secondary  covered,  is  and  similar  this  early  (1940)  feeding  to  flowering  "apparently reference  5  the  In  B  quantified,  was  after  comparison was  not  where  larvae  Nanaimo  variety  accurately of  of  Cairns  to  a  was  seeds,  dates  which  there  monthly  of  defoliated  defoliation  the  jacobaea  of  were  both  o r i g i n a l  instead  Clearbrook  loss  of  production  plants  Hence,  about  crop  while were No  plants. after  I  cut  the  suggest  48  that  their  have  been  spring,  assessment  premature, before  of  since  the  the  "dead"ness"  they  time  at  checked which  of  the  basal  these  plants  plants growth  in  is  may early  likely  to  appear. Bornemissza above seed  the was  begun"  (1966)  ground  when  cutting  nor  does  would  he  results  relating  flowers of  the  not  the  such  a  such  cutting  late  of  called  this  He  the  plant.  feeding  a  late,  plants  the a  possibly  the had  period" given,  the  next  summer.  biomass  and  when  disk-rays  does  the  cm  are  in  in  25  data  period" to  stage  " c r i t i c a l  No  response  " c r i t i c a l  early  the  flowering  browning  plant's  occurs at  the  k i l l  larval  damage  and  l i k e l y  that  that  (when)  plants.  discuss  given  Tyria  and  many  However,  that  ''...during  ripening, k i l l e d  found  exist,  production  development  my show  of  the  " c r i t i c a l " ,  time  summer.  Defoliation In  June  Clearbrook unable possible However, control  15 of  to  the I  of  locate  a  plants  for  the  Perennial  tried  signs  group,  defoliated. September  1971  for  to  and  B and  to  Response examine  regrowth. number  of  After  treatment  plants  only  Judging defoliation  by I  from their believe  a  120  careful  plants.  each  eight  a l l  I  the  were  search  recovered  involving  11  plants  the  P  recovered  f i r s t  group  response  in  the  that  of  these  some  I  14  at was of  a  plants. from to  the be  previous plants  were  dead  collars grass. to  would  1971, and, have  plants  lost were  not  above  A greater  had  growth  this  difference  stems this  in trend  be  1971  than  i s  not  p = 0.05),  repeated  there  new  the  following  this  hypothesis  is  of  broken,  to  find  the  the  two  in  of  defoliated  the  a  clear  growth  of  summer,  plants given  trend  more  died,  and  of  B  plants  (Fig.  produced  5c).  Although  P  B  plants  defoliated  plants  either  or  and  become  additional  perennial.  response  is  consistent,  lead  to  an  increase  over  the  in  a  up  i f  plants  for  to  omitted  have  rosettes  i.e.  long  manner.  controls for  the  I  groups  treated the  plastic  treatments; to  this  the  in  regrowth  assummed Only  should  perennial  one  were  perennial  defoliation of  any  had  of  significant  basal  a  analysis  did  is  with  towards  proportion for  in  )  respond  to  stems  d i f f i c u l t  plants.  proportion  basal  (using  they  dead  the  the  from  found as  i f  very  for  plants  included  mentioned  to  been  Consequently,  two  were  by  normal later  If then  in  level.  the  Evidence  section  of  the  amount  of  fiesults. The  data  secondary during B  in  Figure  growth,  the  plants  production  the  following to  be  but  a  plants  the  similar  trend,  5  suggest  greater  summer.  s i g n i f i c a n t l y  following but  the  the  This  defoliated,  summer  that  as  i s  less  the  likelihood  of  most they  higher (p  the  evident had  differences  for  the  proportion  < 0.01).  P  between  regrowth the  last  lowest  stem  of  plants the  l i v i n g showed  a  different  50  treatments  were  physiological nutrients  not  basis  into  significant.  for  one  the  Whether  apparent  response  or  the  there  is  any  " p a r t i t i o n i n g "  of  other  remains  to  be  investigated. When greater  the  data  capacity  growth,  and  Size  also  of  The  to  and  In  comparison,  in  areas  of  defoliation  in  the  s o i l ,  either  heavier  defoliation  in  plants  that  were  1951  had  there 1967  or  heavily  In  new  on  evident.  Chase  Top  92% of  that  the on  secondary However,  Dutch  dune  by  growth  by  Field at  Lakeside. By  Weeting  larger  way  Heath,  following plants  shoots  in  and  showed  study.  habitat  Tyria  River  stems  growth  secondary  defoliated  the  secondary  a x i l l a r y  to  reported  a  at  of  years  produced  years.  produced  rose  1968.  is  6)  Crops  plants  no  (Fig.  produce  summer  growth  the  was  to  plants  other  (1971)  s o i l  both  of  of  the  plants  Seed  figure  during  Dempster  poor  Normal  86%  histograms  another  secondary  1971  while  P  into  defoliation  occurred  of  as  larger  persist  considerable  regrowth,  Regrowth  plotted the  Secondary  inflorescences.  nearby  of  natural  stimulated  some  are  S.  the  on after  jacobaea  summer  September  of  (Kuenen,  pers.comm.). The secondary  amount growth  undefoliated  of  seed  was  plants  produced  s i g n i f i c a n t l y  (Table  2).  The  at less major  Chase than  River that  reduction  through  produced was  in  by the  51  FIGURE  6  Regrowth of perennial and b i e n n i a l p l a n t s i n June 1971 after production of secondary steins in September 1970. Numbers of biennial plants are in the unshaded p o r t i o n s of the histograms.  Plant Type: P l a n t s S h o w i n g Regrowth in 1971  Plants With No Regrowth in 1971  Number of S e c o n d a r y S t e m s P r o d u c e d in 1970  biennial perennial  52  TABLE Seed production d e f o l i a t i o n , and by  by plants non-defoliated  SECONDARY Top Seeds per Capitulum Capitula Plant  per  Mean Number Seeds/plant  Table Sample  2  Field  after plants.  GROWTH Lakeside  NORMAL  GROWTH  Lakeside  5 0 . 5 ±2.86 (55)  55.6  (55)  (55)  12.4 +3.77 (67)  1 5 . 0 ±3.08 (71)  1 4 9 . 2 ±25.90 (103)  626  834  8,700  of  ±3.19  complete  gives  means  ±2  S.E.  size  given  in  parentheses.  58.3  ±1.78  53  number  of  capitula  defoliation. the  bottom  More  half  (34%) ,  while  reflect  the  therefore  the  few  the  by  defoliated  Cameron  crops  yield  for  the  normal  prevalent the  the  seeds  seed  heads  the  late  controls.  feeding in  of a  a  second  75  of  the to  35-40%,  the  half  crown  to  the  seeds  crop  is  secondary  the  to  in  of  the  number  5%,  5%,  6%  This  where of  to  by  results that a  seed  resulted  from  and  per  a  43%  capitula.  the  the  and  found  plant  seeds  may  88-905?  produced  per  of  areas  and  of  (1966)  capitula  several  one  This  leaves  comparable  crop.  top  (3%) . top  growth,  normal  number  43)  from  Bornemissza  through size  than  axils.  seed  after from  root  of  90%  produced  leaf  100% l o s s  by  were  done  the  reduced  stems  damage  workers.  in  were  secondary  estimated  seed  area.  seed  seed  Bornemissza  of  the  investigated  Secondary  matting  from  other  (1935)  seed  the  developed  of  (from  a x i l l a r y (63%)  12% t h e  reduction  were  stem  buds  83% r e d u c t i o n  new  which  main  plants,  about  plant,  the  the  reduction  reported  an  of  production  crop  of  greater  to  The  per  crops crop  1966). at  this  fine from may  time  seed  may of  rot.  crop  Rainfall  1935;  cooler,  was  the  pappus out  of  Bornemissza shed,  increases  Poole  wetter  reduce  the  dispersing  soon  approximately  (Cameron  The  hairs  mature  10 and  after  Cairns  1940;  weather  effective  together the  weeks  which  seed  and  found  compared  with  abruptly  at  yield  by  preventing  capitulum.  (1966)  is  These that  90-100%  Nanaimo  soggy  only of  from  6% the  a  dry  54  August  to  ripening  wet  and  r a i n f a l l month  a  for  and  The plants  to  with  next  summer  promoted  generally  increase  so,  in  population, I  other to  to  identified  of  as  those  multi-stem  a  of  plant  condition.  My  to  stem  decision  plants  jacobaea  is  i s  ascribe  generally  usually  over  a  assume  as  ground  a  described  as  mm  a  plants.  form.  If  lead  this to  does  not  from plants  having root  the this  plants  "multi-stem"  the  an  in  perennial  from  the  short,  plants  plants  growth two  or  crown.  constitute  condition the  In  investigate  that  level  were  into  survive  should  a  than  to  perennial  those  in  defoliated  produced  To  with  perennial  supported  92  that  biennial  egual.  plants  monthly  perennials  perennial  originates  above  "multi-stem"  I  plants  which  l i k e l y  distinguish  f i e l d .  to  perennials  second-year  of  51  is  Defoliation  defoliation  be  can  Branching  more  repeated  the  from  defoliated  were  crop  1969-1971  showed  become  being  in  each  to  seed  August.  Repeated  perennial  able  In  varied  Clearbrook  factors  plants  stems,  After  proportion  biennial  define  mm i n  defoliated a  secondary  damage.  Also,  and  then  the  had  be  25  l i k e l y  were  the  October  at  growth  than  defoliation  more  to  controls.  secondary  I  13  more  more  form.  and  experiments were  point  susceptible  Distribution  undefoliated  is  when  September  compared  Form  September,  a  to  multi-  literature.  Senecio  single-stemmed,  becoming  55  perennial stems  as  with a  a  result  multiple of  1935;  Harper  stated  that  multiple  by  I  relatively examined  arose  i f  the  opposite  from  older  presence  effect,  perennials.  I  conclude  multi-stem  that  be  In  asssessed  defoliation  multi-stem  by  and  "Tyria  Absent"  defoliation  Tyria  over  3).  pooled,  different  S.  was Q  compared  (p  by  areas <  by  perennials the  0.01). Tyria  the a  number  had of  higher  data  for  chi-squared  the It  are  that  be  At  I  the  A over-  the  would  same  have  the  proportion in  more  to  are  perennial.  plants  of  be  the  f i e l d  common  which  I  perennial  than have  plants  data.  jacobaea a  of  extent  can  plants  present.  of  a)  mechanical  would  perennials  hundreds  markedly  If  were  (1972  plants  plants  proportion  the  where  plants  (Table  actual  of  were  underestimation  although  from  i.e.  1940;  rosettes  multi-stem  perennial  an  Schmidl  multi-stem  crowns,  single-stem  the  areas  a l l  flowering  Cairns  absence  biennial  examining  biennials,  underestimated  several  the  of  and  with  single-stem  causing  After  (Poole  biennials"  of  number  However,  root  of  a  1957).  in  nearly  "multi-stem  of  areas  that  proportion  estimated  cannot  plants  as  -  Wood crowns  suggest rare,  The  time,  and  second-year  injury.  and  interference  Cameron  formed  crown  suffered  years  than "Tyria  the  in  with  distributions  are  therefore  larvae  had  proportion  seems  markedly  of  i  non-defoliated  Present"  test  repeated  data  areas  are  from  the  s i g n i f i c a n t l y l i k e l y increased  that the  56  proportion A of  of  perennial  multi-stem  single-stem  root  systems,  connection each  such  pattern  stem  old is  that  of  number  of  leaves  single-stem The  the  corresponding plants  is  for  biomass, slope  There  n = 230 i s  slopes,  no  stem  plants  contrast, available  and  using  similar  each  for  the  was  the  quite  and  rotting  tenuous. i t s  If  growth  plants.  available  biomass  The  biomass  stems  plants  separate  a  plant,  individual  of  is  multi-  (leaves  plus  is  0.0513x  0.9056  x  of  10~  individual  biomass, 12.95  of  the  leaves, (Fig.  5  stems  8), of  and  the  while  the  multi-stem  for  0.0548X of  the  difference t-test, the  (S.E.  mean  at  multi-stems  rosettes  i s  0.3831 the  p = 0.05.  Both  number  was  between is  slope between  = 0.320)  relationship  biomass  +  variance  Student»s  in  stem  -  x = number  = 0.4151  significant  were  for  i s  +  via  clone  by y  where  -  are  a  have  single-stem  single-stem  = 0.4864  equation  given  and  as  stems  leaf-count/available  y = available of  plants  often  single  to  relationship  variance  other  a  described  stems  tissue  as  areas.  be  the  with  treated  those  better  since  links  y where  in  root-crown  between  plants.  flowers)  the  similar  relationship for  might  plants,  of  i s  similar  plant  and  stem  plants  of  while  (S.E.  the  number  quite  different  s  plant for  mean  12.87  10~ .  regression  leaves the  x  types  single-  leaf  count  = 0.269). of  leaves (Fig.  7).  In and  57  TABLE  3  A comparison of the proportion of multi-stemmed plants from areas with, and without repeated d e f o l i a t i o n by T y r i a .  TYRIA Fort  Bragg  1970  1  TYRIA  ABSENT  1972  Power Pylon  1970  1972  Chase River Road  0.42  0.48  0.65  0.73  0.86  0.78  2  0.21  0.16  0.21  0.19  0.09  0.17  3  0.10  0.16  0.09  0.04  0.03  0.04  4  0.10  0.08  0.00  0.02  0.02  0.01  5  0.04  0.06  0.02  0.01  0.00  0.00  6  0.05  0.02  0.01  0.01  0.00  0.00  7+  0.08  0.02  0.02  0.00  0.00  0.00  1-14  1-9  1-14  1-8  1-4  1-4  2.75  2.34  1.75  1.44  1.22  158  50  102  227  77  Stems/ Crown  Range  Clearbrook  -  Stems/Plant Hean  PRESENT  -  Stems/Plant Plants/ Sample  1.30  205  58  FIGURE  7  R e l a t i o n s h i p between number b i o m a s s on r o s e t t e plants.  of  leaves  and  available  58a  r  59  FIGURE  8  Relationship between number o f biomass on s i n g l e - s t e m plants.  leaves  and  available  59a  2.01  60  FIGURE  9  R e l a t i o n s h i p between number o f l e a v e s and biomass on m u l t i - s t e m p l a n t s . M u l t i - s t e m t r e a t e d here as complex, s i n g l e plants, two o r more stems.  \  available plants are each with  o o o  o oo °  8o'g ^ j 0  r,°'  O  °8g o  15  1  25  o  0  y =0.8096 + 0.0224X (n = 94)  0005^  —1  o  1  1  35  1  1  45  Number of Leaves on M u l t i - S t e m  ;—1  1  55  Plants  61  However, considered are  as  pooled  naturally 1.263),  i f  the  stems  parts  of  accordingly, increases  and  the  multi-stem  as  plant  exceed  therefore  single-stem  plants  in  in  Fig.  date.  Plants  seed  production.  10  probably  a  sampled  at  were  before  inflorescences sampled,  is  of  and  were  Nonetheless,  Fig.  produce  more  increasing not  and  The  in  a  the  the  multi-stem  in  a  level  of  seed  plants  individual  of  stems  be  on  treated may  of  sampling 6,  two  developed leaf  are  in  and  more  the  of  the when  biomass. l i k e l y  the  to  However,  population  production.  or  does  The  over-all  seed plant  production  per  plant,  and  fluctuate  independently  of  perennials.  communities  may  July  biennials.  function  conceivably  defoliation  local  as  seed  is  on  their  perennials  area  proportion  of  than  10),  scatter  the  a  plants  Consequently  plants  total  (Fig.  =  leaf-  Counting  of  poorly  to  that  of  increase  mean  flowering.  perennials  given  Clearbrook  relative  S.E.  the  9).  weight  data plant  31.49,  considerable  were  the  multi-stem  consequence  of  shows  could  impact  jacobaea  small 10  The  plants  proportion  factors  changes  the  of  peak  some  as  necessarily  density both  seed  the  production  the  that  are  per  for  (Fig.  flower  and  was  different  find  plant  count  leaves  relationship I  plant,  leaf  of  i s  plant,  in  weeks  number slope  multi-stem  complex  the  one  points  three  then  regression biomass  each  single  (mean  count/available  also  a  of  be  the  distribution  can  be  as  assessed  complex  treated  as  of in  Senecio two  ways:  single  plants,  or  separate  plants.  The  62  dispersion number  of  of  variance Where  of  a  to  Student's  of  the  the  the  plants  stems  plants  then  areas  Wood  t  the  crown  by  uniform,  would  result  a  a l l  plants  with  with  jacobaea  often  of:  variance The  by  a  single  significant  degree  (Table  4).  as  When  individual  particularly  has  to  a  of  in  the  cover  was  probably  due  to  sparse  than  the  parent, from  areas of  in  I  dense  most  (b)  (c)  the  the  root  vegetation much  in  ,  sampled  Therefore  that  Harper  in  distribution  vegetative  suggested  by  establishment  growth  clumping  also  i t s  near  budding.  continuous  clumping  patchy  land  Most  shows (a)  by  in  be  as  statement  survival.  distributed  to  assessed  the  seedling  Wood  low  counted  low  and  a  and  1964).  tend  treated  sampled  reproduction  a  mean  defoliation.  seeds  root  i s  show  a  distribution.  are  are  a  significant,  consequence  for  ratio  areas  highly  S.  which  uniform  obtained  ways,  the  plants  whereas  in  Harper evenly  a  between  the  plants  consistent  that  vegetative  quite  observed  are  i s  ground,  or  for  repeated  as  tendency  extensive  values  values  result  communities  indicates  several  (Greig-Smith  mean  distribution,  multi-stem  with  the  multi-stem  = 0.01)  ,(1957)  disturbed  t  in  distribution  variance:mean If  the  (p  in  measured  relationship  exceeds  the  of  This and  of  be  the  mean  t-test.  clumping  may  chi-squared  contagious  significance  complex  use  variance  or  relative  plants  which  the  clumped  the  were that  of  the  reproduction.  plants  are  populations.  more The  63  FIGURE  10  Comparison of biomass of flowers and m u l t i - s t e m p l a n t s . Data are at Clearbrook, J u l y 6, 1972.  between single-stem taken from a sample  1.6 1.4 H ^.2\  E ~ x:  1-0-  O )  £  0.8-  e  CD  o  o  0.6-  LL  «  o  0.4 H O  0  2"]  %  o  1  °(£&oo c o ecP  o  o  o  ° o as  o  6* 0  single stems o  o O  multi-stems •  o  o  o  00  0  Oo  "  „ T  •  o  ~T~  -r  2  Leaf  Weight  (gm)  -  8 CT> CO  64  TABLE  4  Effect of larval defoliation on the degree of clumping in different communities of Senecio jacobaea.  Location  v: m  Plants/' Metre  8.77  2. 02  1. 1  4 9 . 99  6. 79  2.9  1.0  m  2  Plant* • t«  2  Stem »t»  Stems/ Metre  2  v: m  Size of Quadrat  2  Fort Bragg 1970 Fort Bragg 1972 P. Pylon 1  6.68  1. 9 5  0.5  48.71  7. 96  1.2  1.0  m  2  9.76  3. 37  2. 1  2 6 . 46  7. 42  3.7  0.5  m  2  P.  7.86  3 . 27  5.0  18.32  6 . 29  8.6  0.5  m  2  Lakeside  22.04  4. 02  2.0  29.91  5 . 11  3.0  0.5  m  2  Clearbrook 1970 Clearbrook 1972 Chase River Road  12.58  4.25  7.3  19.49  6.03  10.6  1.0  m  2  7.43  2 . 86  2. 3  , 9 . 35  3 . 34  2. 8  1.0  m  2  7.96  3.09  6.7  13.42  4.52  8.9  1.0  m  2  Pylon  1  2  Multi-stem  plants  E a c h stem of the separate plant. 2  were  counted  multi-stem  as  plants  single was  plants.  counted  as  a  A l l values of t are s i g n i f i c a n t at p = 0.01. Tyria was a b s e n t f r o m t h e l a s t t h r e e a r e a s l i s t e d in the Table. Locations are ranked from those most d e f o l i a t e d to those l e a s t d e f o l i a t e d , or otherwise disturbed.  65  calculated  t  values  this  suggestion  plant  density  quadrats  cannot  because  between  w i l l  4)  does  areas,  an  t  areas.  i t  of  the  when  stems  are  treated  as  the  stem  v:m  ratio  i s  density  test  areas  and  appears  to  defoliation  and  more  than  be  v:m  directly  to  the  related  plant  non-randomness  be  to  density  (v:m  used The  This for  in  to  increase  plants.  Hence  and  while  pronounced  values.  size  distributions  caution.  rough  of  large  with  the  check  or  can  individual  removes  small  that  an  a  quadrat  variance:mean  indicates  more  as  indicate  of  used  results,  plant  be  w i l l  in  very  plant  clumping  like  defoliated  Often,  ratio  should  directly  change  random  The  index  although  the  quadrats  1964).  give  compared  of  indicate  intermediate-sized (Greig-Smith  be  compare  v:m in  ratio,  clumping  increase  the  the ger  degree amount  in  repeatedly  correlation the  Table  of  between clumping  of  repeated  se.  DISCUSSION The  two  defoliation Senecio  of to  affect  the  jacobaea,  a b i l i t y area,  questions  of  the  local  factors persist.  by  populations  colonize can The  new  in  the  persistence  of  and  plant  defoliation  posed  to  secondly, colonize  Tyria  had  new less on  areas.  At  the  same  adaptations  the of  defoliation  impact  did  the  on  In the  a b i l i t y  time  a b i l i t y S.  were:  jacobaea  of  other of  Does  populations  habitats?  i t  alter  local  does  than  greatly  Introduction  S.  that  lower my  of the  study  persistence the  plant  environmental jacobaea  to  determine  i t s  66  recovery  i n ,  below;  and  or I  evolutionary S.  disappearance offer  role  of  River  immediate  and  within  Tyria  area,  speculations in  10  weeks seed  capitula,  i.e.  shaping  each  number  of  ray  a  seed  of  l i t t l e  cover  was  normal were  some  are  on  the  discussed  the  possible  adaptations  Field  and  Power  but  i t s  In  general,  where  reproductive  effort  However,  Pylon  JSSS^aea (Duffey  to  put to  of  1968).  In  or  to  there these  crop  that  by  10%  of  seed  prevent  (Cameron  seed was  continuous  are  dune  usually  areas  from  probably the  this,  grass  or  1935). ground  could  even There  in  Top  germinate,  probably  minor.  cover  production  numbers.  sand  plants  that was  ground  seed  disc smaller  Clearbrook  populations  produce  a  of  sparsely-covered  secondary  seed  defoliated  this  secondary  is  local  the  At  Chase  number  ringed of  at  first-produced  a  roughly  enough  where  yellow  evolved,  are  established  into  the  However,  dense  local  capitula  to  populations.  there  l i t t l e  in  was  disturbed  contribution  contribute  sand  and  secondary  The  85-90%  2).  becoming  of  a  defoliation  contains  that  that  local  to  similar  Some  (Table  continuous  areas  are  crop  from  produce  flowers)  to  plants  capitulum  plants  seed,  to  florets.  value  by  defoliation.  crops  (individual  undefoliated  was  of  florets  produced  response  Clearbrook  secondary  §•  some  an  jacobaea. The  to  from  the  appears  1  communities large  secondary  expanses seed,  as  where of well  bare as  67  primary  seed,  would  stand  a  much  higher  chance  of  survival.  It  i is  interesting  their  note  parachute-like  dropped  in  retain  their  distance  the  local  are  of  the  ray  ensures  seeds  florets  that  from  potentially  1940).  Because  Tyria  slightly  between  maintained  through  remained  about  50%  the  lose  they  disc  available  in  1968 the  the  are  florets for  long  consequence  of  of  to  of  this  period  plant  being  of  plants  that  several  years  of  (stems  The  per  stem  m )  only  density  was  2  perennials, While  biomass  (A.T.S.  and  and  density  plants.  able  (Poole  multi-stem  other  constant,  fragments  proportion  1972.  being  perennial,  Field,  plant  of  root  high  and  loss  strategy,  from  Top  growth  a  becoming  the  reduced  f a i r l y  over  by  of  by  for  largely  vegetatively  defoliation  compensated  is  reproduction  vegetatively  of  which  reproductive  reproduced  stems  seeds  whereas  and  f l e x i b l e  reproduce  Cairns  area;  persistence  sexual to  the  pappus,  pappus  jacgbaga 's delay  that  dispersal.  . Local  able  to  the  number  showed  Wilkinson,  which  a  of  decline  unpublished  data) . The could  defoliation  not  sufficient next  only  produce  reserves  year.  In  experiments  to  fact  perennial  plants,  than  undefoliated  were  were  a  second  produce both more  showed seed  either  that crop,  controls  to  (Fig.  but  rosettes  biennial, l i k e l y  defoliated  do 5).  and so  that or  more after  plants  many  stems  had the  especially defoliation  68  This prolong  result  S.  suggests  jacobaea  populations  jacobaea  community.  follows:  defoliation  increases are  the  more  and  increase  further  the  multi-stem  plants  would  seem  ability  of  was  function  who  'stress*  plants  found  by  consisted  of  rosettes)  population,  which  exploitation  (or  in of  resist  a  and  (1967),  hierarchy  a  small few  turn  resistance  and  plants  the  by  and  sward.  in A  the  such  the  by  under  population. (in  the  case (large  hierarchies  a  is  similar  plants  individuals  to  where  demonstrated  differences  levels  3)  defoliation  clover  encourages  and  seedlings.  closed  sizes  and  large,  grasses  (Table  individuals  to  in  these  with  within  large  attributes latent  perennials  defoliation.  subterranean  many  Harper  exaggerating  to  and  biennials,  dense  imposed plant  Harper  that  developed  of  a  as  than  Bragg  in  be  perennials  outcompete  Fort  persist  v a r i a b i l i t y  plants). of  the  described  jacobaea,  multi-stem  s t i l l  of  larger  'stress'  hierarchy S.  the  the  (1965),  density The  in  of  phenomenon Stern  plants  at  post-  would  community  effectively  happened  a  these  favour  normally  actually  reproduction  multi-stem  post-pioneer  would  events  defoliation  of  may  usually  plants;  w i l l  compete  have  consequence  increase  perennial  subsequent  can  to  of  is  vegetative  defoliation  that  multi-stem  A  of  closed,  vegetation  large  an  a  what  sequence  proportion  In  This  to  defoliation  into  stimulates  proportion  population.  other  The  resistant  therefore  that  the  within  a  hierarchy  of  defoliation).  69  Presumably, population (see  also  the is  buffered  den  Boer  A similar occurred  in  Holland. seed  "rather  Tyria  the  killed  the  unfavourable  from  jacobaea  on  better  a  conditions  der  became  Meijden many  effect  in  secondary  perennial that  plants  Tyria  dunes  with  found  more of  defoliation, sand  vigorously  proportion  the  to  increased  pers.  comm.).  many  plants  to  (van weather  than  did  on  plant  density  In  Nova  Scotia  Nonetheless  these  crowns,  either  and  by  of  and  defoliate the  to no  the  a  time  "hard  the  level  major for  and  the  plants  original  play  after  (P.  role  in  secondary  early  winter"  1972). factor In  the  affecting poor  produced 1967  plants  to  was  and  another  and  jacobaea,  appeared  there  defoliation.  in  S.  1%  to  Weather  (Harris  small  case.  s u f f i c i e n t l y  since  is  the  control  defoliation,  quality  were  always  reduced  decline,  after  root  S.  k i l l e d  introduced  defoliation  from  types,  recovery  responded  van  not  was  i§£2b.aea  plants  and  large  that  density  Soil §•  a  is  had  plant's  growth  plant  further  of  drought,  however,  population  Harris,  as  of  small".  was  plant  and  concluded  This,  to,  plants  1971).  such He  meet  populations  Meijden  Tyria.  to  range  1968).  Defoliated  factors,  the  response  production,  der  was  wider  no  or  the  through  plant  of  response  Weeting  secondary  1968  recovered  1969  s o i l  the  growth  (Dempster  had  Heath, after 1971).  vegetative  density  of  growth  increased  70  six-fold  over  Figure  5  of  secondary  the  next  growth  that  persistence,  of  both  is  secondary  seed  reproduction.  imperatives seed  for  the of  some  same S.  cost  new  be  crop  the  more  later.  The  for  local  produce  more  selective  i s  'high  value  primarily  risk'  plant's  of  the  I  l i f e  the  into  production?  a  function;  areas  is  the  Most  jacobaea's  colonizing  to  year  strategy  then  distance-dispersal; at  a  amount  survive  (eventually)  seed  vegetative has  effective  and  borne  to  the  perennials  survival  What  growth  between  a b i l i t y  and  plants  plants.  the  trade-off  the  perennial  that  a  plant's  more  reproduction  obviously  the  lower  secondary  for  is  biennials  the  biennial  suggest  mechanism  and  the  and  immediate  I  For  response  do  there  growth  produced,  than  1966.  suggests  summer.  perennial  seed  in  history  produced  cycle  for  seed  argue  as  of  capacity  normal  would  form  a  crop  that  the  require  that  frequently  as  possible. Senecio  jacobaea  selected  species  varying  population  reproduction, common  in  temporary rather  (MacArthur  and  size,  low  colonizing  long-range  habitats  some  and high  species.  for  vegetative  of  the  Wilson  competitive  dispersal  than  shows  1967),  reproductive a b i l i t y .  Colonizers  mechanism  to  which  are  they  attributes  reproduction,  such  Such  the  adapted. is  the  as  an  only  attributes an  early are  effective  scattered Seed  r-  widely  potential,  require  find  of  and  output,  effective  way  71  this  can  be  With  achieved immediate  small,  is  after  Tyria  being  eaten,  produced  defoliated be  four  Seed  has  to  regrowth, year.  least  is  and  no  or  some This  by  with  old,  a  jacobaea.  pupated,  biennial  production  S.  every  at  years  subject  by  greater  second  therefore Tyria.  less  number  i t  however  crop  .matures  in  danger  of  other  hand,  a  production f i r s t  frequent,  of  seed,  never  the  iseed  before  of  seed  is  On  secondary  older,  therefore  quantity  produces  and  unfavourable  may  well seed.  plants  periods  are before  reproducing. This the  argument  relative  secondary crops  the a  risks  seed,  versus  mortality  task  would  stated,  benefits  benefits  smaller  but  local  versus  be  extremely  because  large  more  I  but  regular  periods,  significance  and  not of  and  assessed  normal  and  infreguent crops,  long-distance  have  have  establishment  d i f f i c u l t ,  ecologists  the  of  of  reproductive  of  plant  understand  speculative,  and  the  between  species  is  the  the  seed  risk  importance  to  establishment.  as  Harper  made  few  of  the  Such  (1967)  attempts  of  .  has  " . . . t o  strategy  of  reproduction..." The peak total While  of  main  pressure  f i f t h - i n s t a r biomass,  i t  may  p l e n t i f u l ,  seem  and  of  larvae,  larval  occurred  coincided  advantageous  guality  of  the  feeding, well  roughly to  food  feed may  be  i.e.  the  before  with when more  numerical  the  early food  peak  in  flowering. is  important  most to  the  72  larvae  than  study  on  (1970)  the the  found  quantity  of  closely  related  that  development,  There  i s  factors  a  development the  least  1971), for  and  the  For  l i k e l y their  S.  to  to  vulgaris. values  even  selective  example, starve  and  an  suppose  the  that  early  cycle.  on  Tyria's  larvae  are  (Dempster  favour  i f  in  nutritional  situation  would  Ogden  l i f e  emerging  development  detailed and  operating  outbreak  survival  a  Harper  through  f i r s t  in  occurred  forces  the  in  d i f f e r e n t i a l  emergence  example,  two-thirds  reason  main  rate.  early  about  p r i o r i  are  For  maximum c a l o r i c  seed  no  food.  selection  these  traits  are  feeding  is  heritable. One that  clear  plants  maturation, to  be  used from  result are  from  the  defoliated  which  is  when  susceptible  to  damage.  at  timing  Clearbrook  defoliation  also -  well  Bornemissza The  may  larval  before  of  that  occur  the  (1966)  range  demonstrate  which  of  time  found  S.  over  a  plant wide  seed  jacobaea  defoliation the  of  dates  can  I  recover  period  of  the  summer. Ecological  studies  understanding  the  relationships  between  pattern  of  evolutionary  dynamics  history  discussion  in  shaping  of  the  the  properly  of  about  we  we  evolutionary  adaptations  and  change  organisms.  observe  which  concerned  population  different  interaction  any  are  is  the  usually role  and  know  of  may S.  the  particular  consequence  Tyria  responses  The  with  l i t t l e . have jacobaea  of  an  Hence played must  73  remain  largely  Senecio or  growing  has  once  appears  to  defoliation  developed  growth this  Chemical  and  rule  I  out  strategy  such  through  shortness  tactics  a  as  capacity  selective  of  The  to  are the  delaying  'recovery  production.  the  avoiding  defences  flowering.  the  seed  for  physical  the  c a l l  has  further  and  and  w i l l  i t  strategy  while  growth  defoliated,  vegetative  effective  developed,  vegetative to  no  attack.  not  season  response i.e.  Tyria  or  advancing  by  jacobaea  resisting  ineffective  speculative.  or  plant's strategy',  recover  Has  the  with plant  pressure  exerted  Tyria? If  are  we  no  clear  opposed  to  selection dune  consider  sudden sand,  resistence  pressure with  storms, would  recovery well  the  insect  favour  would of  evolutionary strengthen evolution  a  of  an  before  have that  Such  a  existing entirely  a  of  set.  nature  inundation  adapted  of  by  this to  S.  additional  had  already  rather  sand  such  as  shifting  generalized  an  pressure  the  events  If  adaptations, new  to  displays.  plant  selection  attributable  and  added  the  (as  f l e x i b l e  became  there  strategy  unfavourable  jacobaea Tyria  directly  unstable  risk  such  S.  merely  past. the  just  the  of  environment,  recovery  is  The  risk  total  i t s  strategy)  and  as  its  that  high  type  in  Tyria.  drought,  developed  effect',  from the  strategy  was  plant  indications  a  habitat  the  response jacobaea, 'adverse  faced  in  i t s  would  tend  to  than  force  the  *  74  PART  II.  STRATEGY  FOR  PERSISTENCE:  THE  ADULT  STAGE  INTRODUCTION When by  cinnabar  again §•  a  the  moth  jacobaea  not  a  An S.  the  local  Yet  outbreaks Since  then  success  I  over  a  of  longer  of  a  it  has  local  defoliated and  been  area  when  food  wide  grow  defoliated  than  to  undergoing of  been  survive  respect  danger  the  not  supply  fluctuations  extinction  do  occur  Tyria to  low  than  in  the a l l  one  that same  population  regulation  product'  selection  of  point  local  of  a  i t s  numbers to  I  can  be  operating  agree  on  the  one  caused  the  extinction.  before  the  a  and  favour food  runs  reproductive  mechanism  Bakker as  resource  should  maximize  with  viewed  food  food  self-regulating  time  jeopardize  populations.  selection  uses  defoliation  described  shortage  Tyria  l i m i t  the  (1971)  outstrips  Tyria  in  nevertheless  Dempster  to  that  At  may  numbers,  strategy  the  area  frequently  believe  culminates  subsequent  almost  not  that  large  crash,  the  in  Tyria  plants  when  with  Tyria.  identified.  of  fact,  greater  mechanisms  Within  In  density  when  declines  i n t r i n s i c out.  in  survival  to  in  the  has  fluctuations.  jacobaea  outbreak  of  least  population  minor  population  At  jacobaea  many  year.  I).  increase  of  Senecio  persist  necessarily  undergoing  such  may (Part  therefore,  of  larvae,  following  defoliated  is  population  can  be  (1971)  that  'beneficial  by-  individual,  in  this  75  case  on  both  Host female  the  of  Part  Tyria, where  tested.  Part  Tyria*s and  II  the II  strategy  distribution l a i d  investigate  the  laying  population their  food,  been  adaptive  oviposition Part  density of  the  less  is  II  the the  are  elements  of  the  of most  to  an  in  In S.  of  the  (1968, the  is size  females  I  did  recognize  on  are  being  not host  1973)  have  problem  concerned  of  with  the  recognition. eggs  important  laid  by  The  a  resources  female such  as  studied.  of  individual  much  of  Part  cluster  elucidate  proposed  given f i e l d  moths  papers  is  adaptive  jacobaea.  number  of  the  Schoonoven  to  trait  "How  clusters,  the  of  adult  i s ,  host-plant  for  behaviour  is  of  thoroughly  effects  survival  larval  literature  relative  focus  on  which  and  value  examined  cumulative  of  of  of  on  by  insects;  distribution  have  eggs  mechanisms  behaviour  plant?"  body  conseguences  The  - of  by  eggs  (1960)  considerable  work  oviposition  question  mechanism  a  the  value  host  their  reviewed  physiological  some  of i t s  stages.  with  main  Thorsteinson  and  deals  adaptive  plants.  selection  larval  the  of  invariably  host  and  although  presented In  adult  the  behaviour  II.  Then  at  the  d i s t r i b u t i o n and impact  individuals.  regulatory  on At  the this  during end  cluster  population level  some  will  be  mechanism  identified. Many  insects  density-dependent  are  capable  dispersal  of  regulating  during  the  numbers adult  through stage  76  (e.g. work on  aphids on  adult  this  numbers that  -  and  attempted  occurred  1963;  dispersal  point, I  ADULT  Hughes  in  in  to to  beetles  the  i t s  the  populations  Waloff  cinnabar  determine assess  -  at  moth  1968).  was  possible  amount  Chase  of  Previous  inconclusive  effect adult  on  local  dispersal  River.  DISPERSAL  Introduction Published  data  are  dispersive  f l i g h t s  density  dispersal.  site  in  years, the  on  Fort  that  adults  main of  a  are  not  dispersers.  adult  study  moths  were  seen  van  Dempster der  between did  and  the  the  m in as  and  Heijden's  migratory (1971)  sub-plots not  both  and  of  measure  far  as  der  paper that a  the  at  of  a  diameter  van  found  freguency  effects  infestation 550  very  but  of  only  Dempster  movement area,  area  on  areas  was  1968).  following  local  The  few  (Hawkes  discussion  of  Bragg  although  site  out  inconclusive  release  1.5  60  dispersal  from in  the  suggested  may  be  considerable main  five  km  Meijden,  larvae  adult  after  (1970),  of  the  amount  m by over  90  m  longer  distances.  Other be  a  data  function  1968,  the  (1971)  saw  of  year many  from  Dempster  density, of  but  highest  adults  suggest these  numbers  flying  out  that are  at of  adult not  Weeting the  dispersal  may  conclusive.  In  Heath,  study  Dempster  area.  This  77  observation  was  eggs  was  laid  suggested  that  patch  that  of  showed  an  (which  from  thought  was  occurred  out  cage  measuring  the  increase  he  that  the  number  of  pupal  size".  He  unlikely),  responsible. in  1970  from  or  Dempster  an  adjacent  density.  carried  a r t i f i c i a l l y  had  finding  expected  emigration  adult  and  his  than  mortality  immigration  Dempster  with  lower  adult  high  densities  "far high  considerable thought  consistent  in  high  experiments activity  activity  densities  with that  by  varying  levels.  The  density, are  not  but  moth results  only  approached  at  in  the  f i e l d .  Method I  tried  program any  in  useful The  adult  to  study  1971,  but  estimate  following size,  analysing  of  I  had  and  a  measure  distance .the  fore  each of  from wing  the  mark-recapture  was  too  low  was  d i s t a l  able  a  size  proximate  end  wing  with to  This  moth;  The  designed between  that  occurred.  sampled  size. the  to  fecundity,  adult)  that  from  originally  found  of  measures  was  I  of  rate  a  to  give  movement.  data  (age  with  recapture  hence  measurement dispersal  dispersal  the  method  and  those  adult  method  tip  the (Fig.  the  used  sub-costal 11).  amount  required  estimate I  While  additional  estimate  measure  compare  areas.  one  relative  of  to  I  two  of  age,  was  the  streak  measured  of the  78  left  wing  using  Moths  vernier  were  assigned  characteristics classified their  as  scales,  and the  s t i l l  wing  c i l i a ,  the  lighter  lost  their  moths  had so  pale  many  (n of  June =  27,  126),  Lakeside  lost  no  a  rich  wings.  Class  had  black  scales was  1971  loss and  three Pylon  (n  127).  =  Power  sample  Field  in  their  (n  1972.  heads,  and  red  and  June  23,  were  or  c i l i a ;  vermilion some  wing  wing  c i l i a  shortened,  responsible Class  wing  4  for  moths  scales.  that  dates  in  collected:  140),  Moths  the  on  moths,  wing  lost  was  1  had  had  These  sometimes  transparent.  were  and  or  frayed,  wings  comparable  Pylon  had  their  1 to  emerged  although  had  of  bright  coloration.  almost  On  Newly  with  scales  dull  =  class  scales  adults  of  samples  Power  2  red  be on  wing  adults  most  to  tear.  black  wing  very  done  from  removing  and  as  3  of  age  s l i g h t l y ,  dull  and  collected Top  faded Class  c i l i a grey  Sampling On  had  1,  the  wing  relative and  intact. and  a  wear  was  under  to  wing  Class  colour  were  lost  of  coloration  markings  callipers.  126  were  from  an  1972 from  and  from  Top  area  100  111  1972. Field m  moths  Lakeside.  k i l l e d  measured  1971  I  immediately  west were  did  not  by  my  to  sex  later.  Results The and  age  mean class  apparent.  wing as  There  lengths  shown is  in a  were  Figs.  11  consistent  calculated and  12.  trend  according Two  towards  points  are  small-sized  79  males  as  lacking  the from  Part of  of  the  loss  of  wing The  scales;  an  i s  change  these  Class  newly  included  to  Because  there  Classes I  3  the  samples earlier  4  in  observed sex-linked  4.  of  Why  are  the  three on  summer  than  male t r a i t  to  1)  are  the  do  reduced  taken  a  few  one  is  applicable  only  due  as  of  0.570  mm f o r  Class  their wing  length  values  be  female  compared. data,  in  size  are  of  we  small would  size  the  with  males  in  caught? The  yearly  moths  emerged  obtain  explanation  would  to  i t  males;  to  remains.  large  explanations.  the  similarly  in  males  1  c i l i a ,  can  decrease  wing  wing  individuals  moths  and  microscope  older  i f  wing  mm l o n g ,  data  so  of  the  modified  male  old  to  length  the  not  most  mean  comparable  day,  This  to  classes  large,  large  distribution.  that  and  measure  0.27  proportion  possible  is  dissecting  correct  smaller,  so  mm t o  to  individuals a  the  a l l  made  when  in  lost  two  is  to  'be  trend  males,  females  mm a n d  these  (Class  trend  With  used  of  referred  0.21  0.628  had  be  But  of  determined  for  moths moths.  from  was  can  means  consider  were  I  adjustment  wings  and  is  adults  lengths  must  w i l l  4  correctly  mm l o n g .  1 males  Class  the  the  type  micrometer  this  adjusted,  more  0.69  similar  length  were  Class  Class  wing  which  emerged  older  mean  c i l i a ,  4 so  When  in  length  are  a  females.  wing  scale  c i l i a  for  whereas  mean  c i l i a  ,As  older,  in  0.48  for  females.  age  the  ocular  c i l i a  in  data  one  another  grow  the  change  length.  and  moths  the  require  thus  a  seems  80  unlikely. there for  Moreover,  was  no  either The  partially  wing  third  for  female  moths  below  suggest  If often  sluggish warm a  are  in  days  number  of  test  small  in  the  laboratory  date  and  adult  size  large  this  less  a  the  males  males  quickly  hypothesis,  evidence  However,  suffer from  but  (1971)  the  i t  that  is large  similar  that  activity  males  are  smaller,  less  w i l l  i s  data  therefore  dispersal  l i k e l y  to are  hypothesis  for  females  disperse. indeed is  not  l i k e l y  decrease  d i f f e r e n t i a l trend  function  dispersive  dispersal.  similar  a  more  d i f f e r e n t i a l  females  the  more  females.  larger  through  of  larger  published.  behind  that  If  males. in  the  the  data  of  larger  implies  The  generally  to  that  observations poorer  necessarily  f l i e r s  refuted  by  females.  female feign  that  eliminated  to  reflect  hence  for  than  thus  lack  males; data  of  truly  the  the  and  classes  moths,  is  Dempster's  been  leaving  males  than  reared  emergence  p o s s i b i l i t y assumes  length  age  are  data  by  not  proportion  older  no  longer  have  emigrate, The  have  lived  The of  I  and  refuted  males  pupae  between  p o s s i b i l i t y  mortality  females  40  sex.  population.  for  correlation  second  greater  amongst  moths death  cool they  are  disturbed,  instead  weather tend  moths  in  to  when be  the  of  then,  unlike  flying.  Also,  males  less f i e l d  are  active and  s t i l l than paced  males, they  are  active.  males. off  I  they very  Even  on  disturbed  the  f l i g h t  81  FIGURE  11  D i f f e r e n c e s i n wing l e n g t h between samples of adult male Tyria jacobaeae of d i f f e r e n t ages f o r three locations. Means are shown with 95% confidence l i m i t s . Class 1 designates the youngest moths; Class 4 the o l d e s t . L o c a t i o n s were s a m p l e d on June 27 i n 1 9 7 1 , and on June 23 in 1972. Numbers of males c o l l e c t e d ( w i t h 1971 f i g u r e s f i r s t ) were : Top Field 6 7 ; P o w e r P y l o n 8 1 , 74 ; L a k e s i d e 6 6 , 9 8 .  81 a  Length  o1971  • 1972  20n  To p Field  19  18-  £ £  Po we r Pylon  20-  0 CD C  ®  19-  o  Lakeside  0  20-  0  0  19-  1  Age  C l a s s - Males  FIGURE  12  Differences i n wing l e n g t h between samples of adult female T y r i a jacobaeae of d i f f e r e n t ages for three locations. Means are shown with 95% confidence limits. Only two C l a s s 4 moths were caught i n Power Pylon. These data a r e o m i t t e d . Age i n c r e a s e s from C l a s s 1 t o C l a s s 4. A r e a s were s a m p l e d on J u n e 27 i n 1 9 7 1 , a n d on J u n e 23 i n 1973. Numbers of females collected ( w i t h 1971 f i g u r e s f i r s t ) were : Top F i e l d 59; Power P y l o n 5 9 , 3 7 ; L a k e s i d e 6 1 , 2 8 .  O  19-1  ® 1972  18-  Top Field  0  17H 16  1971  82a  J  19-|  £ E  •-  si  •*—•  Q) CD  1  6  1817-  Power Pylon  0  • -  •  O)  d  1918-  0  0  Lakeside 0  6  1716  1  2  Age  3  Class -  Females  4  83  FIGURE  13  Winglength in male function of pupal separate containers. a f t e r t h e y had f u l l y  and female T y r i a j a c o b a e a e as a length. Pupae were kept in The w i n g s were measured s h o r t l y hardened.  83a  Pupal Length  (mm)  84  distances. whereas and  The  average  females  averaged  lighter  (Fig.  13),  females  which  for  If  abdomens must  length 2  m per  than give  one  can  dispersing  by  calculating  Class  Class  for  the  1972  by  after  loss age  4.  of  class  t-tests  had  a  Males and  was  have  also  wing  c i l i a .  each  13m,  smaller  larger  wings  advantage  over  that  in  of  values I to  the  in  were  pooled give means  adult  means  data  between  corrected  for  larger  were  male  proportion  f i r s t  the a  the the  difference  4  area  occurring  estimate  the  Class  showed  males  considerable  is  rough  all  for  by  flights.  population,  1 and  f l i g h t .  a  dispersal  make  f l i g h t  females,  them  long-distance  d i f f e r e n t i a l  of  197 1  sample  not  and size  s i g n i f i c a n t l y  different.  For (n  =  Lakeside  24)  equivalent  and to  data the  0.306  standard  by  would  need  to  would  have  dispersed.  the  Class top  amount be  truncated,  the  (n  i.e. Top  dispersal,  to  account  mean  = 25)  Field  4  11% of  for  equal  To  the  11%  Power  the  the Pylon  Class  amount  the  s h i f t  50% of  the  largest of in  Class (n  shift  Class  of  the  the  mean  distribution  of  for  exceeds  to  the  Class  i.e.  1  15%  In  4  top  Similarly  Class  dispersed.  Class  the  between  deviations.  truncated,  1 mean  15% o f  difference  corrected  mean  the  this  the  4  1  mean  =51)  was  the  Class  1  distribution  largest  moths  data,  shift  mean  would moths  truncation, the  1  Class  distribution,  to (n  =  need  to  would and 1  52), be have  hence to  although  of the the  85  small  sample Such  of  the  number  (16,  16)  make  truncations moths  of  dispersed  values Pylon  abrupt  largest  greater have  sizes  do  do  to  not  remain  medium-sized cause  the  in  15% d i s p e r s i n g  are  minimal  estimates  estimates  impressions appears  to  density  of be  was  population  adult  highest,  and  Further  work  size  and  i s  more  rigorously.  extensive present dispersal dispersal  was  on  by by  females.  from  of  some  Therefore  a  w i l l  need  to  shift.  Hence  the  Lakeside  rates  these  Field,  lowest  use  i f of  suggests  adult  Top  in  wing-loading  mark-recapture evidence  area.  as  and  Power  agree  areas. where  from  with  Thus the  my  dispersal population  Lakeside,  where  the  lowest.  necessary The  reality,  moths  amount  males  unreliable.  only.  density from  in  local  large  dispersal  greatest  density  age  of  occur  same  11% and  estimate  the  and  of  These  this  males  one this  and were  may  to  method  program that  activity  would a be  test in  as  functions  this  hypothesis  conjunction  also  be  occurring,  with  valuable.  considerable with  of  amount much  an The of less  86  S I Z E OF  EGG  CLUSTERS RELATIVE TO  PLANT BIOMASS  Introduction Many  species  of  Lepidoptera,  particularly  the  t h e i r e g g s s i n g l y ; o t h e r s l a y them i n  large  butterflies,  lay  clusters.  The  g y p s y moth, f o r e x a m p l e , l a y s f r o m  eggs  one  in  cluster  (Weseloh  1972) . The  300  to  500  c i n n a b a r moth  also  l a y s i t s eggs i n c l u s t e r s , u s u a l l y 30 t o 50 eggs Although  both  biotic  size,  one  major s e l e c t i v e p r e s s u r e ,  with  a  very  and  limited  f o o d a v a i l a b l e on  the  a b i o t i c f a c t o r s may  range of  1959b);  lays a large  must a l l o c a t e a g r e a t e r searching In  f o r new this  host  d i e when t h e  proportion  section  host plants.  of  plant  and  My  i s the  biomass.  number o f s m a l l of her  I examine the per  energy  p l a n t s i n the feed  the  wished  various  large  of a  (Dethier  clusters  she  reserves  to  r e l a t i o n s h i p between  c l u s t e r and  the food  t o combine  extensive  a p p r o a c h was  cluster  I  amount  food r u n s out  distributions  at  Chase  to c a l c u l a t e :  populations  that  (a)  were  the  the  available surveys  River  e s t i m a t e s of l a r v a l s u r v i v a l , f o o d consumption per food  species  plants.  a v e r a g e number o f e g g s l a i d on  time.  affect cluster  host p l a n t . I f a female l a y s too will  i f she  a  p a r t i c u l a r l y .for  host p l a n t s ,  c l u s t e r , many l a r v a e but  at  with  larva,  and  proportion  of  large  enough  to  s u r v i v i n g l a r v a e from the a v e r a g e - s i z e d c l u s t e r ;  (b)  87  the  actual  upon  proportion  which  between  female  the  indication  of  In  this  were  the  only  the  adaptive  individual  when Tyria from  the  plant  host  egg  value  female  clusters  the  population  the  f i n a l  moth.  relative level.  section  of  to  way one  These Part  (b)  cluster that  those  clusters.  and  will  by be  i.e.,  size  with  that  moths  another  has  consequences  A  plants  difference  should  plant,  cluster The  just  discrimination  on  of  egg  (a)  each  cluster  considered  laid  results  analysis  egg  one  give  some  Tyria. treated I  am  as  i f  assessing  reference  to  distribute i t s  w i l l  i t  the their  consequences be  at  explored  in  II.  Method After sampled  several  follows. with  two  pairs  some  Each lines  of  locations sample of  to  be  and  Senecio  in  area  stakes  random  quadrats a l l  preliminary  the  was  at  numbers  sampled.  in  1970  Chase  divided  gave m  2  into  plants  the of  a  to  1971  area  quadrat in  grid  other. of  the  I as  rectangular each  treated  May  study  coordinates  each  were  and  River  right-angles  A 0.5  jacobaea  work  Two 1  m  2  was  sampled,  the  following  manner. Before being  examining  'above  1  the  surrounding  to  divide  or  each  plant  'below',  vegetation.  plants  that  I  classified  i.e.  ' t a l l '  This  c l a s s i f i c a t i o n  could  be  or  its  'short'  encountered  height  as  relative  to  was by  a  intended moth  that  88  simply  flew  those  that  at  random  would  the  vegetation.  of  leaves  eggs  on  lens Egg  to  count  those  so  to  one For  additional  food  the  ground.  I  of  the  data.  touching.  5  the  plants  plants  that  were  to  If  I  or  many  these their  from  the  of  units these  same  within number  absence  any a  x10  counted  so  I  was  leaves  as  root  to  growing were  provide  disperse plant  clumps,  hand  able  their  to  an  across  clumps.  and  I  twice.  were  plants  of  eggs  plants  having  feeding  or  used  usually  adjacent  constituted  growing  and  more  from  the  found  hatching,  two  that  height,  ground,  after  these  that  presence  were  herbs,  actively  the  clusters  without  more  and  the  leaf  out  small  plant  from  larvae  source  noted  cm,  and  the  leaf.  another  refer  sought  Sometimes  feeding  grasses  each  Large  on  be  recorded  height  remain  the  to  than  them.  include close  then  underside  their  cases  have  longer  the  recorded  I  above  also  I the  crown.  Results In  June  around Power  a  of  pile  Pylon,  Lakeside.  I  difference  The  the  of  and  two  and  total  clusters  in  number  contained  sampled  of  in  closely these leaves  between  locations  I  stumps  pooled  cluster- density  of  1971  a Top  population Field,  adjacent latter  per  Similarly,  Power  Pylon  plants  12,950  eggs.  I  S.  jacobaea  populations  populations after  showed  no  pooled  the  referred  sampled  three  results  plant  them.  of  to  exceeded  as  t-tests  of on  significant data  Power  1500,  west  in  for  two  Pylon  2.  and  the  328  89  My on  f i r s t  analysis  rosettes  density  of  presented of  and  showed on  a  as  vegetation  on  or  c l a s s i f i e d .  moths  tended  t a l l  actual  laid  for  cluster  Top  Field  mean  was  because which in  of  eggs  being  when  only  t a l l  laid plants  surrounding  was  no  longer  were  less  l i k e l y  how of  results  those  the  is  are  numbers  the  three on  total  compared  moths  The  results  the  than  laid  frequency,  so  difference  clusters  cluster  plants  clusters  Clusters  the  plants,  more  were  However,  Nonetheless  lay  When  were  the  most  rosettes  four  locations  stemmed  plants  than  rosettes.  The stemmed  to  short  locations,  taller  This  clusters equal  probability  5).  i.e.  6).  with  plants  (Table  i f  location.  compared,  (Table  below  each  higher  above,  were  on  for  stemmed  were  significant lay  between  plants  c l a s s i f i e d  to  varied  s i g n i f i c a n t l y  stemmed  determine  plants  separately and  to  stemmed  clusters  rosettes  was  (Table in  size.  were  cluster  7);  each Mean  29.49; then  size  cluster  pooled used  similar  conseguently  location  Power  size  was  and  sizes  in  Power  I  for  rosettes  could  calculate  P y l o n (1+2) for  on  one  and  pool mean  the value  each  location  were:  44.74;  Lakeside  44.14.  Pylon  subsequent  and  Lakeside;  calculations  was  the 44.62  eggs. Before the  larvae  estimate  determining surviving  the  food  i f  from  plants a  available  were  large  mean-sized on  each  enough  cluster plant.  The  to  support  I  had  to  equations  90  TABLE  5  A comparison of the frequency of o v i p o s i t i o n by T y r i a on r o s e t t e s and stemmed plants of Senecio jacobaea. Sample s i z e i s given i n ().  Clusters L a i d On Rosettes  Location Top  Field  Clusters/ Rosette  Clusters L a i d On Stems  Clusters/ Stem  C h i  2  52 (370)  0.141  36 (62)  0.581  20.43* df=1  P.Pylon  1  65 (231)  0.281  53 (66)  0. 803  28.65* df=2  P.Pylon  2  27 (303)  0.089  46 (175)  0. 263  13.21* df=2  14 (204)  0.069  35 (159)  0. 220  8.35* df=1  Lakeside  •Significant  at  p =  0.005.  Chi tests compare 0 , 1 , 2 , . . . clusters/plant plants. 2  on  the distributions of rosettes and stemmed  91  TABLE  6  Frequency of o v i p o s i t i o n on S e n e c i o j a c o b a e a plants when t h e h e i g h t i s c o n s i d e r e d r e l a t i v e to that of the surrounding vegetation.  Loca tion T.Field  Plant Height In Veg.  No. Of Rosettes  Clusters/ Rosette  No. Of Stems  Tall Short  109 26 1  0.321 0.065  54 8  0. 556 0.750  2.22  2 —  Clusters /Stem  Chi  2  -  d  P.Pylon  1  Tall Short  65 166  0.600 0. 157  62 4  0. 839 0. 250  3.21 —  3 —  P.Pylon  2  Tall Short  74 229  0.243 0.039  166 9  0.277 0. 000  0.01 —  —  Tall Short  96 108  0.104 0.037  148 11  0.236 0. 000  3.56  2  Lakeside  —  Chi tests compare the distributions of 0 , 1 , 2 , . . . clusters/plant on rosettes and stemmed p l a n t s . No c h i values are s i g n i f i c a n t at p = 0.05. Sample size of stem plants was too small for a s i m i l a r comparison between s h o r t plants. 2  2  2  92  TABLE  7  S i z e o f egg c l u s t e r s l a i d on p l a n t s at Chase R i v e r , 1971.  CLUSTERS f  ON S T E M S  Sample  4.911  94  5.400  99  44.74  5.715  92  7.988  35  55.00  24.363  14  2 8 . 18  4.318  44.74 39.80  Lakeside  ROSETTES  30.41  Top  Pylon  ON  66  Mean  Power  CLUSTERS  stemmed  Mean  Location Field  and  S . E, (x2)  S.E. (x2)  Sample Size  rosettes  Size  Results of Students-t t e s t s i n d i c a t e d t h a t f o r no l o c a t i o n were t h e r e s i g n i f i c a n t d i f f e r e n c e s (p=0.05) between cluster sizes on rosettes and stemmed plants. Cluster size v a r i e d s i g n i f i c a n t l y between Top F i e l d and o t h e r a r e a s c o m b i n e d : t = 6 . 1 0 7 , 390 d . f . , p<0.001.  93  regressing  available  were  used  were  l a i d ,  which  the  time  larvae  had  to  give  increased,  A  an  was  also  more  larvae  plant  by  a  was  1.33  to  Conversion  in  number that  in  of  some  rosettes  The  estimated  stemmed  location were  weights  of  and  included  is  the  mean  weight in  of  Table  than  t a l l  than  omitted  because  of  (e).  actual the  These  single  clumps.  means  and  an  increase  most  of  the  To  estimate  there  in  plants  the in  the  (e)  is  units'  are  a  range  were  for  biomass  the of  leaf  short  the  short  plants; size.  those  The  larvae in  in  Columns which  and  biomass Col.  mean would  data  plants,  particularly  in  plants  given  in  from  jacobaea  from  stemmed  varied  Field  that  single  a l l  Top  Most  sample  calculated  variance:  in  S.  to  of  increase  stemmed  small  wider  biomass  the  expected,  populations  were  rosettes,  Hence  the  'feeding  different  As  on  by  ranged  from  plants  eggs  available  and  derived  rosettes.  t a l l  plant  factors  date,  8)  the  multiplication  food 8.  7,  However,  food  These  single-stem  purpose.  given  of  proportional  this  when  instar,  the  were  (Figs.  sampling.  sampling  lighter  in  by  leaves biomass  f i f t h  factor.  factors  and  of  estimate  the  from  of  plant  the  were  the  encounter  for  to  lighter  plants  were  plant  and  marked  rosettes  (d)  4  were  each  data  Fig.  of  obtained  conversion  according  v  number  time  accurate  location  curve  the  reached  each  1.45.  on  estimate  had  f i f t h - i n s t a r weights  biomass  large values  (d),  as  rosettes.  proportions  that  had  sufficient  biomass  94  to  feed  9)  I  used  1)  and  larvae  two  survival  two  Appendix  larval 2,  accurate rate  the  Very survived  on  few  not  to  this  of  lay  on  at  i t  Stemmed  proportion  with  enough  cluster  higher  much  higher  From  the  calculate for  the  0. 093,  that  Only  42%  a  stemmed plant  However,  some  of  stems  better  estimate  given  in  and  these or  of  Table  rosettes)  were  is  9 (d)  had for  the  larval  given the  high  in more  feeding  the  rate  as  are are  The  tendency  of  adaptive  and  larval  of  0.138. in  with  with  lay  on the  (b)).  rate  How  rates. we  can  enough  food  rate  9(c),  and,  of  in  unit'.  plant  clumps,  them.  Hence  sufficient  individual  of  average  'feeding  larger  plant  the  survival  with  (  and  and  Table  contact have  to  survival  separate  where  from  9(c)  plants  of  not  that  although  biomass:  a  a  in  along  adaptive,  feeding  part  plants (e),  9(b)).  (Table  examined  treated stems  larvae  larvae  low  68% f o r  are  the  feeding  proportion  assessed  (Appendix  gives  the  (Table  for  more  the  rosettes  was  food  more  for  and  have  rate  therefore  seem  food  many  instar I  while  (Table  plants  rosettes how  feeding  enough  survival  is  f i f t h  pupation  limit.  cluster  plants  each  other  low  at  mean  cluster for  reasons  had  (c)  addition,  1. e.  on  in the  average and  than  depended  results  For  would  a l l .  was  rates.  rosettes  evidence  rosettes  to  upper  average  to  egg  consumption,  rosettes an  through  for  the  food  the  cluster  rates  believe  gives  from  a  feeding  estimate  l i k e l y  Tyria  I  from  biomass  plants  clumps.  a is  (stems  Plants  in  95  TABLE  8  Estimated biomass of r o s e t t e s , stemmed plants, and plant clumps plus i n d i v i d u a l plants. A clump i s two or more p l a n t s whose leaves are in contact. A l l plants are separated in Cols, (a) t o (c), and i n (d) and (e) plant clumps are treated as single biomass units.  Location  Short Bosettes (b)  Tall Bosettes (a) 0.942  Tall Stems (c)  Tall Plants+ Clumps <<*)  Short Plants+ Clumps (e)  1  ±0.155 (109) 0.25-6.67  0.65 ±0.047 (261) 0.25-3.89  1.59 ±0.182 (54) 0.59-3.48  1. 8 0 ±0.309 (116) 0.25-9.64  0.81 ±0.089 (201) 0.25-3.89  Power Pylon  1.18 ±0.202 1 (65) 0.32-4.65  0.70 ±0.063 (166) 0.24-2.80  2.37 ±0.329 (62) 0.90-7.28  3. 89 ± 1 . 144 (62) 0.48-24.0  0.84 ±0.100 (123) 0.24-2.80  Power Pylon  1.00 ±0.127 2 (74) 0.31-3.62  0.69 ±0.047 (229) 0.31-2.70  3.24 ±0.268 (166) 0.55-10.9  5.65 ±1. 987 (118) 0.31-86.0  0.83 ±0.105 (135) 0. 31-4.64  0.83 ±0.070 (96) 0.31-1.86  0.59 ±0.049 (108) 0.31-1.56  2.70 +0.292 (148) 0.67-14.4  3.47 ±0.700 0^2) 0. 31-28.6  0.76 ±0.106 (82) 0.31-2.67  Top Field  Lakeside  *A p l a n t c l u m p i s c l a s s i f i e d as least one plant i s above surrounding vegetation. 2  Each  c e l l  l i s t s :  /  being the  mean b i o m a s s (g d r y ±2 S.E. (sample size) range of biomass.  ' T a l l ' level  weight)  i f of  at the  96  TABLE  9  Proportion of plants with s u f f i c i e n t food for the f i f t h - i n s t a r l a r v a e s u r v i v i n g f r o m an average-sized c l u s t e r . A c t u a l d i s t r i b u t i o n of c l u s t e r s on plants i s not c o n s i d e r e d .  Location  FR  1  Sur  2  Tall Rose. (a)  Short Rose. (b)  Tall Stems <c)  Tall Plants +Clumps (a)  Short Plants +Clumps (e)  Top Field  L L H H  0.093 0 . 138 0.093 0 . 138  . 16 .05 .04 . 02  .05 .01 .01 .00  .72 .34 .21 .07  .52 .35 .29 .16  .13 .06 .05 .02  Power Pylon  L L H H  0.093 0 . 138 0.093 0 . 138  . 13 . 06 .03 .02  .02 .01 .00 .00  .60 .31 .23 . 10  .60 . 44 .42 . 28  .07 .01 .00 .00  L L H H  0.093 0 . 138 0.093 0 . 138  .07 .01 .01 . 00  .01 .00 .00 .00  .80 .58 .42 * . 18  .63 .49 .43 . 33  .08 .01 .01 .01  L L H H  0.093 0 . 138 0.093 0 . 138  . 02 .00 . 00 . 00  .00 .00 .00 .00  .60 .43 .27 . 11  .54 .43 .36 .22  .05 .00 .00 .00  1  Power Pylon  2  Lakeside  •-Feeding R a t e s a r e : Low = 0 . 4 4 0 g/larva; High = 0.744 g/larva (Appendix 2). S u r v i v a l Rates are given f o r the end of the f i f t h i n s t a r (Appendix 2  period: 1).  egg  to  the  Assumes a c l u s t e r s i z e o f 2 9 . 4 9 e g g s f o r Top F i e l d , and 4 4 . 6 2 f o r a l l o t h e r l o c a t i o n s . C l a s s i f i c a t i o n of clumps i s given below Table 8.  97  (d)  were  heavier  proportions in  9(c)  includes  the Table  many  cluster.  could Does  to  laid  which  can  s u f f i c i e n t l y the  proportions  Table  9 (d)  randomly  with  I  improve  females this  and  In  we  listed  fact,  in  the  feeding  each  cluster  was  same  on  plants,  females  results  or  in  relation  heading  plant.  'Low  clusters  Table to  would  other  in  the  (d).  to  feeding  rate.  plants  appropriate  are  almost  90%.  In  mortality  rates  in  clumps,  10  also  size.  Rate'.  have  had  plants  in  show  We  on  the  small  the  that  sufficient  food  on  clump,  10 (b) eggs  of  values  seen  plant  other  plants.  have  the  were  more  importance  Consider  to  Table  proportionally  than  values  they  figures  lay  on  clearly  The  to  biomass that  regard  higher  if  plants  those  is  and  plant  on  low  that  without  cluster  Feeding  numerous  10 ( b ) ;  value  rates  N  considered  tended  plant  Table  The  as  egg  be  just  eggs?  mean  similar  the  assess  laid  10  on  when  actually  are  50%.  when  is  an  respect  figure  values  support  in  the  the  whereas 9(d)  concluded  at  that  plant  in  of  plants  pupation  and  the  lower  stemmed  to  indicate  of  are  explanation  larvae  9  the  few  The  the  Tables  in  to  only  yet  corresponding  would  than  clumps  rate.  8) ,  the  clusters  higher  The  very  than  (Table  the  answer  larger  lower  9 (c)  50% of  Tyria  clusters  in  includes  estimates  average,  this  used  feeding  rosettes  were  feed  which  low  rosettes,  the  clusters on  were  locations  From  those  9 (d)  9(c)  The  different  then,  in  at  follows.  than  plant under  almost their  i f  any,  90% host were  98  included with  (Table  the  food  48% (10 (a))-.  Feeding  74%  24%  If feeding  out  of  turn  larger  is  Here  to  (c))  the  can  we  conclude  fact,  not  probably  low  to  could  larvae  value  made  for  decrease  feeding  the  very  that  have  would  "not  was  compared  dropped values  was  to  under  greater,  from  .  (10(b))  In  plant  mean be  mean  the  enough  host  this  to  before  answer  the  again  small food.  only  comparison  Rate*.  units  usually  same  ( 1 0 (d)  we  If  requirements,  The  •High to  10(b)).  the  the  and  average  cluster  start  the  running  was  larvae  run  and  the  size out  actual  cluster  fifth-instar  mean  much",  rate  be  of  much  food?  reason  is  The given  below. The cluster 8.  Top  and  food  needed  can  be  Field  In  rate  1.21  was  survival,  and  rates.  These  weights  for  small  Top  locations feeding  of  Field  g  food  rate  was  cluster  mean  food  required  close in  required per  rising  to,  or  would  at  the  cluster,  other  survival  g  with  high the  (d).  food.  in  low  immediately  insufficient  Table  those  and  and  in  size,  1.79  exceed,  8(c)  mean-sized  cluster  the  to  survival  Table  size  from at  a  weights  because  different  high  from  plant  were  with  g  surviving  separately  with  given  1.83  the  cluster,  are  larvae  the  the  per  3^03  in  with  needs,  values  Top  larvae  treated  Field g  to  increases  proportion  be  food  locations.  the  compared  w i l l  therefore  by  high  feeding  mean  plant  Hence  even  increase For  low  survival  2.71  g  with  the and  high  the other low  larval  99  TABLE  10  The e s t i m a t e d p r o p o r t i o n s o f egg clusters laid on plants that were large enough to feed the larvae f r o m an a v e r a g e cluster to pupation. The actual distribution of clusters i s used. Each c l u s t e r is t r e a t e d as i f i t were the only cluster on that plant.  LOW  FEEDING  Host Plant Alone (a)  RATE  HIGH  FEEDING  Host Within Clump (b)  Host Plant Alone (c)  Host Within Clump (d)  Location  Surv  Top Field  0.093 0 . 138  .57 .38  .95 .83  .27 .09  .81 .67  1  0.093 0 . 138  .45 .26  .91 . 87  .22 . 12  .83 .81  2  0.093 0 . 138  .63 . .49  .95 . 86  .40 . 29  .86 .71  0.093 0 . 138  .63 .4 1  .90 . 82  .37 . 14  .69 .55  Power Pylon Power Pylon  Lakeside  ^Survival  1  rates  are  2  derived  3  in  Appendix  RATE  1.  A l l plants are assessed i n d i v i d u a l l y ; other plants i n clumps are ignored. If a cluster i s present, then t h e f o o d r e q u i r e d by t h e s u r v i v o r s from the means i z e d c l u s t e r i s compared with the p l a n t biomass. 2  If a plant i s in contact biomass of that plant clump i s with the food r e q u i r e d .  3  with other plants the summed and compared  Cluster sizes are given b e l o w T a b l e 9 . Number c l u s t e r s sampled was: Top F i e l d - 8 8 ; Power P y l o n - 118; Power P y l o n 2 - 7 3 ; L a k e s i d e - 49.  of 1  J  100  survival, rates.  and  4.58 g  Again  the  mean  is  a  these  biomass  greater  (Col. (d)). to  u t i l i z e  most  CLUSTER  two  of  high  higher  stemmed  margin  This  adapted  with  biomass,  of  food  VARIABILITY  on  the  cluster the  AND F I R S T - I N S T A R  to,  feeding  or  exceed,  although are  there  considered  size  larvae  average  high  close  clusters  mean and  are  and  (Col. (c)),  plant  that  plant the  values  plants  when  suggests  survival  from  i s  closely  one  cluster  plant.  SURVIVAL  Introduction If for  the  the  cluster  e f f i c i e n t  question size?  mean  larger  Why  other  clusters,  i s  and  thus  Dempster  (1971)  has  young  larvae  suffer  a  do s m a l l  Lepidopteran 1960)  which I  larvae may,  reared  i f  group  I  measured  clusters.  in  feeding  in  survival  favour  that  large  of  group  loss  different-sized  in  cluster or  cluster  clusters to  of  predators sites  (e.g.  cluster  by Ghent  size;  conditions  development  the  smaller,  feeding effort  different  and  i n  v a r i a b i l i t y  and grouped  survival  adaptation  biomass,  favour  proportional  a  an  v a r i a b i l i t y  establishment  solitary  of  the  a  as  plant's  much  suggested  sometimes  affected  a  pressures  maintain  The  turn,  larvae  so  lower  is  regarded  of  there  selective  size.  than  can be  u t i l i z a t i o n  arises;  Possibly  size  to  rates;  egg c l u s t e r s  in  see and the  101  f i e l d . the  I  f i r s t  occurs that Yet  examined instar  (Appendix cluster  i t  one  i s  only  than  on  of  t a l l height  see  this  survival w i l l  of  have  no  the  ,size  have  inadequate  l i k e l y  a  to  already for  later  larvae  group,  on  examined  small  plants  that  larvae  imply  development. from  that  short the  f i r s t - i n s t a r  shown  mortality not  in  the  oviposit  on  do  in  the  measured.  I  against  I  when  survival  larval  discrete  be  6).  ground)  food  although  form can  on  highest  instar,  (Table the  size  consequences  discrimination I  1971),  s t i l l  less  (above  the  f i r s t  cluster are  cluster  when  has  plants  value.  of  Dempster  eggs  moths  cluster i f  1;  during  effects  Female  impact  only,  size  cluster  direct  the  to  many  plants  effect  of  survival had  immediate  small  complete  to  plants  development.  Methods Early selected and  in  59  10  cluster  on  clusters  were  number  ground  were The  "rounded  and  laid  were  plants  plants  i t  height,  days.  oviposition  stemmed  another  clusters  the  on  also of  these  the plants.  followed  recorded,  yellow",  and  and  three  Lakeside.  during  f i r s t - i n s t a r and  around  near  leaves,  period  the  of  mid-May  woodpiles  Each  next  plant  three  Many  in  of  these  the  f i r s t  height  of  clusters  were  count  was  taken  which  was  usually  Field egg  additional  instar.  checked when  an  I  additional  through  clusters  Top  had  weeks  1971,  from  the  every  2-3  larvae  three  Plant  days  were after  102  hatching. To  investigate  survival  I  Fifteen hatched, groups, as  raised  importance  30  larvae  singly  larvae  were  placed  on  and  15  were  f i r s t  each  of  fifteen  controls,  that  the  used  and  for  each  the  larvae  group  through  separate  allowed  larvae,  was  of  to  were  the  in  as  their  raised a  for  larval  f i f t h  plants  f i l l  established reared  feeding  on  instar.  soon  as  they  stomachs.  separate  similar  Two  plants  manner  to  singly.  Results Data  on  collected  and  98  clusters.  Three  for  survival);  each  l a i d .  figures  areas;  but  11).  Thus  were  around  were  survey  400 sizes  lowest  for  not  the a l l  clusters, did the  f a l l  were  laid  and  analysis  variance  showed  survival  clusters  values  hatched;  of  data  the  were  larvae/eggs  a l l  when  survival  hatched/eggs  therefore  clusters  was  eggs  s i g n i f i c a n t l y  grouped  cluster  survival  not  decreased  of  An  f i r s t - i n s t a r  were  First-instar size,  cluster:  f i r s t - i n s t a r  larvae/eggs  four  mortality  for  calculated  survival  egg  were  size  with  the  mean  cluster  chosen sampled in  smallest  this  different  with  at  50  survival  size  of  random; random,  range  cluster  that  these  between  increasing  exceeded  highest  at  f i r s t - i n s t a r  the  pooled.  increased  cluster  (egg  39.3 but  showed  (Table  class  an  and  7). thus  cluster  eggs  (Table  (30-50 eggs.  eggs) These  independent that Egg the  mean  survival trend  103  TABLE Effect of cluster s u r v i v a l . The mean error.  Eggs/ Cluster 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 100+ F  N 13 21 22 22 7 2 4 4 2 1  .  *Data used.  size on e g g , and f i r s t - i n s t a r i s followed by i t s standard  Egg Survival  Instar I S u r v . A*  Instar I Surv. B  .81 (.045) .91 (.036) .93 (.035) .91 (.035) .84 (.062) .91 (.116) .86 (.082) .98 (.082) . 9 2 (. 1 1 6 ) .13(.164)  . 33 .42 .57 .59 . 36 .64 . 39 .32 .48 .50  .30 .38 .54 .57 .28 .59 .31 .31 .44 .06  *  value P  2  (.068) (.053) (.052) (.052) (.093) (.173) (. 1 2 2 ) (.122) (. 1 7 3 ) (.245)  not  distributed  *Survival hatched.  i s  given  as:  Survival laid.  i s  given  as:  normally;  (.063) (.050) (.049) (.049) (.086) (. 1 6 1 ) {. 1 1 4 ) (.114) (.161) (. 2 2 8 )  2.94 <.01  2.08 <.05  are  2  11  F-test  f i r s t - i n s t a r f i r s t - i n s t a r  cannot  be  larvae/number larvae/eggs  104  was  accentuated This  laying  small  mean-sized  clusters,  or  the  plotted  the  cluster  a  off a  crowding one  Their  very  is  and  not  Instead from some  explain  one  must  tentative  wide  explain than  why from  explanations.  that  survive  from  hatching  are  once  cluster  size  exceeds  50  effect  of  small  larvae.  threads  are  moths  the  mean-sized  When  dislodged,  easily  discrepancy  from  young  was  larvae  favour  density-dependent  silken  leaf,  does  should  several provide  broken.  may a  positively  f a l l  is  be  larvae in  tenuous  It  Dempster's  may  a  link  not  clear  finding  that  correllated  with  size.  Factors  other  survival  larvae  larvae  that  and  i t  offer  suggests  is of  I  level  packed  but  B).  selection  higher  they  o r i g i n a l  there  be  of  the  that  clusters.  clusters.  reaction.  survival  low  should  through  tightly  of  numbers  This  chain  why  size  (Fig.14)  operating  with  in  large  If  are  Survival  suggests  survival  eggs.  11,  result  v a r i a b i l i t y larval  (Table  to  survival  of  than small  establish or  hypothesis  a  d i f f i c u l t  clusters  were  arthropod  predators.  important  influence may  vary  I  rates to  reduced  suggest  such  responsible  The  a b i l i t y  appears  (Fig.  15).  to that  survival that  be  site  test:  almost  on  must  clusters.  feeding  development  is  Lepidoptera  crowding  the  large zero egg of  of  for  individual  not  to  Dempster's as  (Fig.  well 14),  quality small  last-laid  affect predator  as  small  possibly  may  clusters. eggs  the  are  have Eggs of  by an of  lower  105  FIGURE  14  Survival of f i r s t - i n s t a r l a r v a e as a f u n c t i o n of number of eggs h a t c h i n g . Sample s i z e = 96. Data from Top F i e l d (n=81) a n d L a k e s i d e (n=15).  o  the are  47.1065X  34.7336+x  Number  of E g g s  Hatching o 03  FIGURE  15  Survival and r a t e of development of T y r i a l a r v a e in s o l i t a r y and grouped c o n d i t i o n s . A l l t r e a t m e n t s were run simultaneously, and i n d o o r s . Larvae i n (a) and (b) were r a i s e d i n i s o l a t i o n u n t i l Day 8, and were subsequently raised in pairs. Larvae in (c) and (d) were r a i s e d i n groups of 15. Treatments (a) and (c) were started prior t o any l a r v a l f e e d i n g , whereas (b) and (d) w e r e s t a r t e d when l a r v a e h a d a f u l l gut.  106 a  Days  (a)  Solitary  (b)  Solitary  (c)  Grouped  107  quality I  than  present  Tyria  those  evidence  section  indeed  There  was  no  height  instar  survival  (Table  12).  survival clusters point. short  the  i s  lowest  than,  plants  and  they  do  frequently rosettes  should lay  short  (Table  6),  but  the  based  on  data  zone  where  In accruing of  plotted  spite to  of  laying against  expressed  shows  egg  and  of  the as  20  cm  are  eggs  favour  the  do  tend  to  is  in  the  most i s  clusters  adversely  For  When  the  cluster  increase  in  from  survival height data  which  avoid  on  the of  were  the  survey  by  one  16  is  of  egg  above  the  height.  benefit  knew  both  the  incubation  time  is  relationship  can  the  I  larvae  Figure  affected  was  less  smallest  young  laid  for this  oviposit  well.  clusters their  more  on  there  28  cluster  ground  independent  disadvantages  hatching.  as  First-  establish  survival  inadeguate  size.  moths  above  only  i s  linear  to  and  cluster  minimum  although  particularly  not  of  a  needed  of  poorest  well  Moths  clusters  the  the  above  therefore  that  height a  had  height,  of  effect  of  of  laid.  cluster  height  that  clusters.  of  the  clusters  survival  these  low  by  any  1970).  clusters  eggs  size  of  Leonard  small  last the  independent  collected  and  cm)  supply  the  Therefore  plants, where  food  distribution, (0-6  their  select.  on  lower,  say,  be  1965;  that  between  suggest  independent  Selection  plants  be  affected  data  higher  to  ground.  w i l l  was  The  later  likely  the  survival  ground;  a  correlation  above  on  be  in  are  height  date  (Wellington  eggs  their  the  f i r s t - l a i d  incubation  time  with  108  TABLE Effect of cluster s u r v i v a l . The mean e r r o r ().  Cluster Height (cm)  N  3-6 6-9 9-12 12-15 15-18 F  P  24 45 26 2 1  *Data used.  h e i g h t on egg, and f i r s t - i n s t a r i s followed by i t s standard  Egg Survival  Instar I Surv. A  Instar I Surv. B2  .84 .93 .86 .98 .99  .31 .54 .52 .72 .44  .28 (.047) .50 (.035) .46 (.046) . 7 0 (. 1 6 4 ) .44 (.232)  (.036) (.027) (.035) (. 1 2 6 ) (.179)  *  value  1  (.049) (.036) (.047) (. 1 7 0 ) (.241)  4.29 <.05  are  not  •-Survival hatched.  i s  given  as:  Survival laid.  is  given  as:  2  12  distributed  normally;  4.31 <.01  F-test  f i r s t - i n s t a r f i r s t - i n s t a r  cannot  be  larvae/number larvae/eggs  109  FIGURE  16  Height at which eggs are l a i d r e l a t i v e to the height of the p l a n t . Data a r e from Power Pylon sites and are only for unhatched egg clusters. Data for hatched eggs were e x c l u d e d as plant height could have been considerably lower when the female's c h o i c e o f o v i p o s i t i o n s i t e was made.  109a  ' • ^  o  o  CD "CO  O  O  CM "CO  o  CO 'CM O O 'CM  o o  8  <b  o  o o o o o o o o o 0 0 8 <6o o o o o O<2P8 O  o o  "CM  .CD  LCM  °OCoO  o cP o 0 0 0 o 0 0 8 0 0 8  CD CO  —1— CM CO  00 CM  1  t  CM  (UJO)  r —1 o  —  CM  ja^snio  —I—  CD  jo  1  1  CM  ii]6!9[-|  r  00  •CO  o o  —r—  o  •o  o D)  X c CL  110  FIGURE  17  R e l a t i o n s h i p between c l u s t e r height above the ground and the l e n g t h of time needed f o r egg development. Data are from Top Field and Lakeside. A l l egg c l u s t e r s were l a i d between May 17 and 26, 1971. Incubation time i s independent of o v i p o s i t i o n date.  cP  H e i g h t of C l u s t e r  Above  ,  Ground  o  (cm)  111  height  above  which  approaches  description reduced  the  i f  younger  larvae  on  larvae  have  III).  Therefore  cluster  of  over  their doing  so  OF  a  to  chance  a  to  are  probably higher  CLUSTERS  a  Because ground  PLANT  in  AND  is  time  a  not  plant  the  over but older  one  actually advantages  more  younger  (Part  benefit  moths  the  LARVAL  of  plant  occasional  the  The  known;  could  few  by  better  advantage  another  the  a  clusters.  from  so  outweighed  be  consequence  food  finding  mortality  PEB  a  function  included.)  competitive  incubation  the  would  were  lowest  disperse  cluster.  close  value  limited  of  lowered  curvilinear  heights  the  have  with  forced  (A  probably  reaching  eggs  of  greater was  plant  better  17). asymtotic  larvae  another  disadvantages  NUMBER  at  heat  are a  upper  time  older  larvae  (Fig.  clusters  radiated  Whether  lay  an  incubation  increased  when  ground  freguent  larvae.  SURVIVAL  Introduction In  the  hypothesis enough  that  larvae  average, Two one  previous  to  one  be  egg  consume  plant.  predictions  follow  lower;  and  cluster  of  Part  cluster  most  single-stem  averaged-sized  should  sections  of  from is  therefore  II of  the  on  females  have  put  average  food  this  laid  I  size  available  hypothesis: a  foward  plant should  i f  larval lay  the  produces from  the  more  than  survival only  one  112  cluster  on  any  one  plant.  survival  when  the  evidence  that  females  plant,  presented  in  the  hypothesis  is  that  is  The when  only  with  each  one  two,  or  small  percentage l o g i s t i c s  cluster  experiment  their  laid I  setting  were  on  the  egg  a  larval  increased, clusters,  and  larval  clusters  more  up  w i l l  plant  examined  than  an  and  one  per  three  Even  collection  greatest  w i l l  decrease  plant,  with only  clusters, series  as  and  be  survival  per  additional  formidable.  involved  is  survival  standardized has  examines  section.  larval  is  plants  of  plants  next  section  clusters  space  cluster.  three of  of  do  cluster  additional  one,  the  number  This  a  and  of  four-  designed  the  counting  of  1800  larvae.  Method The and  experiment  standardized  the  impact  holding I start  of  plant used the  associated  was  groups  size  and  experiment. with  39  Concurrently  f i r s t - i n s t a r i  numbers  and  summer was  Field I  of  most The  Chase  measuring a  on  a  f i r s t - i n s t a r  mortality.  calculated  plants assess  plant  while  constant.  old,  the  selected  therefore  clusters  eliminated  in  with  could  size  two-day  This  I  Top  larvae.  f i r s t - i n s t a r that  in  cluster  approximately  counted  to  of  different  clusters eggs.  done  the  mean  to  variability of  400  study  area  was  survival  from  egg  River  larval  rough  of  larvae  estimate  size  of  about  50%.  113  Therefore  I  survivors  used of  20  the  f i r s t - i n s t a r average-sized  larvae egg  to  cluster  represent to  that  the  stage  in  development.  I and  placed  replicated  larvae  was  put  replicates plants.  To  and  I  were the  up  with  18.  more  replicates  After  Field  where  plants  without  was  15.8.  number The  in  40,  on  larvae  walk  up.  each  was  on  Larvae  had  single-stem  density fences.  was The  checked was  low mean  group  five  5  cm)  was  similar  5.8  onto of  the  on  the  tin  experimental  around  cylinder  was  preparation free  are been  to  the  started  I  in  an  enough  to  risk  two  coated  out  of  plants  in  set  area  on  five  of  Top  these  days  counted  two  days  the  fourth-instar  after  up  leaving  or  on  larvae  disperse  "fenced"  count  plant.  that  plants  leaf  each  one  after  20  flowering  every  terminated,  of  plants.  were  plants  Each  rosettes  single-stem  (>  each  commercial  These  instar  of  three  established  moving  top  of  times.  leaves  treatments  were  I  cylinders  a  Tyria  experiment  high  the  five  larvae  from  Fluon,  tin  60  each  single-stem  the  for  on  leaf.  of  around  these  Plants  and  the  however.  Fig.  larvae  treatment  7 cm  to  enclosure  60  number  other  unable  or  separate  20,  collar  outside  a  12.3  set  A plastic  on  mean  stop  plants  40, each  with  The  rosettes,  the  20,  plants  and  each  the  the  moult.  count.  114  Results Survival with  one  due  (Fig.  unfenced plants  the  plants  60  larvae  with  were the  A l l  14)  might  declines,  food  completely  of  eaten;  cluster  rosettes  before  being  III).  well larvae  on on  are  Thus  survival  the  value.  former  disperse.  delay So  plants plants  in  although  had  20 a  1,  and  had  food  a  five that  within  two  larvae at  the  third-instar larvae.  While  precipitous with  the  factor.  for  rosettes larvae  they  had  later  time larvae and  the  the  left  the  a l l  The  was  2  of  dispersing the  with  yet  to  mostly  larvae  associated  been  time  in  36),  of  as  not  were  three  for  advantage  larvae  On  fourth-instar  density  longer  to  the a  unfenced  have  appeared  exception  numbers  dispersal  only  the  0,  plants  clusters,  numbers  43,  s t i l l  8  three  The  responsible  could  the  was  (26,  low  i n i t i a l  forced  successful  positive  been  in  the  third-instar  to  and  on  i t s e l f  plant.  of  plants  supply  Regardless  per  instar  7  by  supply.  plants  yielded have  food  density-dependent  diminishing  (Part  two  with  declines  dropped  these  other  (9,  predators  had  highest  plants  numbers  fourth  numbers  On t h e  sudden  large  was  crowding  of  respectively.  more  Larval  on  exhaustion  into  larvae  lowest  the  the  time.  and  instar  as  there  moulted  fourth  18).  survival,  to  days  the  cluster,  predicted affect  to  40  to  on  the  for  one-  feeding  the  instar,  to  new  larvae  per  advantage  the  plants  dispersal  survived  considerable  were  is  of  equally plant, given  115  FIGURE  18  Survival clusters five repl numbers different unfenced  of larvae from on t h e p l a n t . Each i c a t e s . The v a l u e s of days of food l e t r e a t m e n t s . These plants.  d i f f e r e n t numbers of egg point is the mean of i n b r a c k e t s a r e t h e mean f t f o r each l a r v a i n the values apply only to the  Larvae  per  Plant:  20 40 — 60  Rosettes-fenced  Single-Stem Plants "fenced A  Instar  ~ Plants  S i n g l e  S  -unfenced unfenced  Ul  »  116  the  food  larvae right  supply could  of  s t i l l  remaining.  continue  to  feed  on  The  number  those  plants  of is  days shown  that on  the  Fig.18.  SPACING  OF  CLUSTERS  BY  FEMALE  TYRIA  Introduction Larval cluster should  survival  on  a  space  given  plant.  their  plant.  I  only  the  average  The  two  lines  presents from  the  (by  and  large  -  of  another  a  is  more  than  predicted  that  Tyria  lay  or  only for  small  result  leaf  plants,  and  presented and  on  any  being,  the  am  concerned  a  below  data  hypothesis.  that  where  time  egg  females  cluster  the  behaviour, this  one  one  plant.  evidence  support  on  there  single-stem  unexpected  ovipositing  laid  therefore  oviposition  maturation  when  ignoring,  by  with  on  I  am  posed  observations  lower  clusters  complications  egg  is  on  This  moths  are  cluster  has  -  the  f i e l d rate  section  not  of  also  inhibited  previously  been  female).  Methods I Tyria study  made while area.  consecutive  many  casual  engaged In days,  in  notes  other  May  1971  but  could  I  on  f i e l d  the work  watched not  egg-laying in  one  afford  the  female  the  time  behaviour Chase  of  River  moth  for  three  to  do  this  117  more  than  once.  I  become  sluggish  without  being  Pupae the  of  were  a  kept  late  moths.  I  k i l l e d wing  of  in  was  that  the  fine  pair  evening  and  can  hour female  time.  cut  the  at  that  could  tweezers  were  be  so  my  without  my  were  without  being  f l y i n g  inside  c l a s s i f i e d  mature  eggs  ovipositing.  in  the  The  eggs  this the  was  age  an  and  counted  were  for  a  "mature  squeezed  c y l i n d r i c a l laying,  class  that (see  time  was  estimate the  also of  moth  egg"  with  a  while  they  wire  mesh  generally they  were  Dispersal  was'' c o u n t e d ;  abdomen  when  they  Adult  the  continually  f i e l d  At  early  emergence,  the  accurate  abdomen  the  found  cluster the  in  chorion.  After  I  estimate  after  gently  in  the  field-collected  Eggs  in  during  sources  the  enclosed  egg in  and  both  breaking  cages.  to  and  criterion  disturbed.  as  killed.  Presumably  mature  night  in  accurate  abdomen,  handled  Some  of  moths  the  collected  times  present.  eggs.  number  for  usually  indoor  the  laying  and  since  checked  From  an  was  different  open  ovarioles  egg  both  and  were  with  Emergence  sometimes  details),  night  caged  emergence.  were  caught,  be  moths  moths  for  females  eggs  of  Tyria  started  a l l  containers  female  Female  cages  day.  25  length,  developing  were  moth  afternoon  mature  of  the  Some  emergence  or  number  watch  separate  an  of  morning  measured  in  half  total  their  the  period.  within  obtained  in  not  disturbed.  emergence  f i e l d  did  for  and  the  counted  that  the had  number  of  stopped  118  On leaf.  several The  females  following  would,  carried  an  lighted  room  cage.  In  cluster  on  contained in  water  were  or  egg  experiment  was  designed  not  cluster.  with  6  vials  lay,  Four  were  the  lower  surface.  a  leaf  and  which  stayed and  leaves  fresh  daily  and  without  were  put  other eggs.  in  days. each  window, to  each  maintain  leaves  with  oviposition  period  was  had  an  egg each  stalks  were  1  females  two  in  to  four  different  cage.  the  each  vials  Class for  i f  naturally  within  leaf  cage  same  already  a  that  were  in  to  in  four  The  the  that  kept  leaves  on  determine  c i r c l e  clusters  changed  clusters  The  to  leaf  a  jacobaea  egg the  a  in  of  clusters  were  several  was  to  cages  free  for  with  relative  S.  was  one  on  arranged  vials  locations,  leaves  two  two  The  checked  found  would  I  egg  caught,  days.  occasions  Leaves  2:1  were  ratio  of  clusters.  Results The see  Tyria  captured the  mean  main  females for time  spent  laying  moths  often  oviposition 50  seconds,  apart.  laying  dissection being an  eggs  12.00  laid  between  approximately  stayed  15.00  cluster  in  the  for  the  f i r s t  although  the  last  rates  afternoon.  before  a l l  average-sized  the  same eggs eggs  of  h.  h.  The  30  13.00  and  Although  eggs  position was were  I  one laid  was  as  16.30 the  2-3  every much  not  females  as  h;  time  roughly  for egg  did  1  h,  h.  The  25  to  8  min  119  Since tended  to  probable rate.  afternoon spend  that  after  1  one  Moreover,  given  oviposition, laying  My  days  three  confirmed laid  The  to  a  moth  started  to  remained  more  great  many  lay;  It  there  I  eggs. move  moved  for  moths  was  2  in  The  cluster,  the  on  the  one  the  moth  at  17.10;  1 m onto  some  h,  with  l i t t l e  with  a  and  again  females  were  plant.  Tyria 14.15  was  over  seemed  oviposition  given  on  temperature  u n t i l  a  females it  morning  that  cluster  found  the  average  unlikely  one  and  one the  flew  observations  pattern.  not  day  than  norm,  laying  seemed  this  did  the  h  per  that i t  of  was  3  cluster  deliberately  had  laying  female  h  when  i t  18  C.  i t  had  about  3  h  since  herbaceous further  plants  and  movement  that  evening.  The  next  temperature  day  of  19  during  the  between  flights.  were  doing  shorter  f l i g h t s  the  moth lower  rested  a  this  and  during  f l i g h t s  of  leaf  started  (30  and  about  leaves.  It  leaf  laying  eggs  min  when  a  maximum  several  metres  to  the  over  spent  2  S.  moth  and  a  min  min  i t s e l f at  moths  was  very  series  of  small  'examining  jacobaea  later  hour)  of  crawling  positioned  an  other  exploration  before  5  and  most  12.40  another  briefly,  of  3 m each  the  onto  breeze  total  with  Jacobaea then  a  noon,  12.20  and  light  rests  Between  ragwort S.  flew  long  interspersed  leaf  examined side,  of  moth  with  four  several  underside  blackberry  It  sunny, The  likewise.  making  and  C.  morning  active,  herbs  was  onto leaf. on  12.45  1  a The the  h.  It  120  laid 55  42  eggs,  min.  By  oviposition On  behaviour Between  2  It  third rested  11.28  and  a  selected at  12.05,  moth  then  flew  13  and  had  had  become  of  these 12.00 S. S.  the  the  the  jacobaea  cm a n d  I  days  or  plants,  The  data  from  newly-emerged  of  egg  emergence sized*  maturation  females since  was  complement  of  probably  pupation actually  a  f u l l  from  laying  before  a  m in no  other  over  h  the  a  occasion.  an  plants, area  of  started laid  few  feeding  many  within  low  38  1  laying  eggs.  herbaceous  suggest of  to  her  lay  before  (Fig.  eggs.  The plant  size  a  female's  (Fig.  19b),  immediately had  19a).  a  far  f i r s t  upon  'cluster-  Conseguently,  v i c i n i t y  How  their  that  moths  immediate  laying  3  point.  eggs  the  any  having  moths  day  on  12.00,  function  mature  before  disperse  a  at  this  unlikely  disperse  site  i s  are  i t  at  of  from  23  observed  a l l  12.55,  the  stay  metres  covered  moved  on  a  sluggish.  time.  remained  after  few  moth  leaf  at  moth  a  moth  jacobaea  stopped  16.40  guite  three h  at  moved  lost  that  moths  i t  morning  and 50  plant  I  rate  min.  a  the  most  few  eggs  for  and  during  including m .  site  but  left  19.30  the  f l i g h t s  and  of  their  female  moths  eggs  was  not  determined. Figure reserve As  the  these  when  20b  shows  they  had  maturation  moths  would  be  that  most  finished rate  was  moths  laying not  a  high  physiologically  had  few  cluster it  seems  capable  of  mature in  the  eggs  f i e l d .  unlikely laying  in  that  another  121  cluster  immediately;  the  lower  the  same  i s  plant.  reserves doubt  Class  mature have  a  for  the  female  1 females  enough  Tyria  oviposition  site  a  cluster  the  same  clusters  female  do  an  time  w i l l  appear  immediate  time  on  FACTORS  Tyria  in  the  between  lay  two  to  second late  clusters,  clusters  have  on  sufficient  cluster,  afternoon  jacobaea (Table  already react  These  at five  CLUSTER  in  when  leaves  13). the  carried  but to  I lay  On  the  same  moths  laid  one  when  I  cluster.  noted  Nor  towards  occasion  time a  already  subseguently  f i e l d a  selecting  that  I  negatively  egg-laying.  ovipositing  INFLUENCING  S.  occurring  to  during  discrimination  eggs  that  appear  plant.  no  against  leaves  moths  moths  jacobaea  of  showed  phenomenon  Tyria  ovipositing five  longer  that  eggs  Individual  found  §•  chance  the  cluster.  carried  new  of  they  another  an  the  and  on  total  of  do  other  I  found  one  small  159  eggs.  SIZE  Introduction The as  few  as  strongly factors dynamics some  number 5  to  of as  eggs many  correlated affecting of  physical  Tyria and  in as  a  160.  with  cluster  cluster  populations. and  Because  cluster size  biotic  varies  In  larval  size,  may  help  this  factors  considerably:  is  understanding  the  to  the  section  that  survival  from  elucidate I  w i l l  influence  i  examine cluster  122  FIGURE  19  Development of from emergence  eggs of T y r i a as and wing l e n g t h .  a  function  of  time  (a)  Y = 11.6447+1.2058x r = 0.79 (p<0.00l)  °  ~*  20 Hours After  i  40 Emergence  —r  60  (b)  Y =-144.7950 + 114.4808 x r = 0.51 ( p < 0 . 0 1 j 15  16  ~Y7  . Wing  Length  18 (mm)  19  123  FIGURE  20  Effect of age of female Tyria m o t h s o n (a) the n u m b e r o f e g g s l a i d p e r c l u s t e r , a n d (b) t h e number of mature eggs retained after oviposition. Each point in (a) i s the number o f eggs l a i d i n a c l u s t e r i n t h e f i e l d . The same moths were l a t e r d i s s e c t e d to determine the values i n (b). The means f o r e a c h age c l a s s are g i v e n ± one s t a n d a r d error.  Number of Mature Eggs Retained in Abdomen i  -J. O l  I  M O I  I  CO O i  l  Number of E g g s in C l u s t e r  4^O  !_  124  TABLE Effect of oviposition  13  egg clusters on s i t e by f e m a l e T y r i a  INITIAL CONDITION OF THE L E A F  NUMBER  the choice moths.  OF  CLUSTERS  Expected  Absent  23  24  Cluster  Present  13  12  A t o t a l o f 36 e g g c l u moths. The ratio, with cluster present, o f c l u s t e r s l a i d was random l a y i n g w i t h r e  an  LAID  Observed  Cluster  of  s t e r s were laid by 16 Tyria l e a v e s w i t h no c l u s t e r : leaves was 2 : 1 . The expected number based on t h i s r a t i o and assumed s p e c t to egg c l u s t e r s .  125  size.  The  data  presented  here  are  from  f i e l d  work  and  f i e l d  observations.  Results I  regularly  study  of  examined  most  The  plant  mild  the  per  with one  with  some  in  by  but  the  Many  skies moths  oviposition day  (42  with  the  d.f.)  the had  age  h.  cleared,  of  fewer  the  laid  lower  and  sun  of  May  the 24  female eggs.  that  were  laid  size  are  shown  The  from  Top I  suggest  followed  by  having  (pooled)  showery,  h  onwards. 16.00  that  the  gave  a  clusters a  t  h, low  clusters  accumulated  comparing  had  by  larger  was  rain  and  15.30  Field  21  morning  and  cool  per  Fig.  May  shone  in  in  Airport.  was  each  laid  Nanaimo  25  I  therefore  clusters  24.  my  period  could  egg  May  t-test  clusters  and  temperatures  moths A  one  during  new  on  sun.  was  eight-day  from  of  value  the  larger of  May  of  1.83  0.07. factor  female:  mature  data  the  For  of  morning  in  mature  major  but  plants  clusters  cluster  ovipositing  plants  p =  egg  was  marked  daily,  (number  mean  The  remaining  and  One  rate  sunshine,  rate  of  new  cluster  through  complement 25  egg  were  on  of  the  70  plants  meteorological  15.00  especially  next  and  to  survival.  these number  day)  Only  set  of  oviposition  together  60  f i r s t - i n s t a r  determine day.  checked  affecting older  eggs .in  cluster  females  reserve  laid  after  size fewer  appeared eggs  oviposition  to  be  and  also  (Fig.  20).  126  FIGURE  21  The effect of daily variations in sunshine and t e m p e r a t u r e on t h e r a t e o f o v i p o s i t i o n and size of e g g c l u s t e r s . O u t o f 69 m a r k e d p l a n t s , 59 t o 69 w e r e examined daily f o r new c l u s t e r s . On May 27 o n l y 10 p l a n t s were e x a m i n e d . O n l y one c l u s t e r w i t h 7 eggs was found on the 24th, whereas on t h e 27th two clusters of 29, and 45 eggs were found. Other c l u s t e r means a r e shown w i t h one s t a n d a r d error.  co  Maximum Daily  of S u n s h i n e •  I  _*  1  r\j I  -J.  I  o> •  Temperature N>  '  o !  I  |\3 I  i  O  1  1  O  1  1  O  Ko  " _ P Oviposition R a t e (clusters/plant/ciay)  i  1—n  CO  O  Eggs  1  A  O  per  1  1  01  o  Cluster  r  127  Fecundity  and  of  adult  (Dempster  to  affect  1971  rate  cluster  moths  of  egg  1 9 7 1 , and  size.  were and  Lakeside.  ranking  egg  per  cluster  in  Power  Lakeside  larger  in  =  Females not  (n  were  do  of  v a r i a b i l i t y  not  consider in  Ovipositing  females  their  leaves.  easily  equal  =  and  with  in  be  this  (by  size  with  might  support  160),  and  44.7  expected idea.  Power  eggs  eggs  size  wing  cluster  44.1  find  laying  Pylon  sizes: per  per  In  length and 29.5  cluster  cluster  to  a  spot'  freguent  of  on  while  terminated empty  be  jacobaea  found  occasions  'an  ovipositing,  degree  generally  they  while  Senecio  their  some  that to  disturbed  size.  in were  On  f e l t  i n a b i l i t y  serrated  191),  cluster  variable  I  (n  increase  Field  correlated  interrupted  extremely  females  data  Top  of  Field =  19b),  f i e l d on  both  at  49) .  I  segmented  Fig.  and  was  Top  Pylon (n  Some  smallest  measurements), This  maturation  the  source  leaves  are  segmentation. broader,  watching  narrow  less  ovipositing  egg-laying on  and  because  segments  of of  leaves.  DISTRIBUTION  OF  CLUSTERS  AND  PLANT  OVERLOADING  Introduction In  an  earlier  clusters  in  four  average  cluster  section  locations size  with  I at  examined Chase  the  the  River  biomass  of  distribution and  of  compared  plants.  I  egg the  concluded  128  that  the  larvae  u t i l i z e  most  surviving of  the  hypothesised  that  cluster  given  space  on  a  their Those  oviposition  omission Tyria  is  are  sections  were  to  be  population  shall  use  describe  of  the the  examine  some  f i n a l l y  to  larvae  a  that  how are  at  showed  with  the  the  as  and  the  when  individuals Birch  (1954)  egg-laying.  It  is  do  of  the  the  host  plant  distributions run  out  moths of  determines  food  the the  population.  I  populations  to  clusters,  to  distributions,  affect  is  population  sum  Tyria  of  i t  in  the  the  of  female  over  affect  density  of  that  of  This  environment  eggs  pattern  the  the  the  River  with  of  out,  lay  Chase  value  rises  to  four  to  moths  pointed  other  where  the  in  of  l i k e l y  I one  level.  density  activity  these  and only  not  population  major  that  that  and  component  the  lay  adaptive  moth,  consequence  other  clusters  factors  should  major  on  from  results  individual  but  distribution  see  consequence,  could  manner.  the  clearly  data  plant;  concerned  what  The  egg  average  l i t t l e  decisions  distribution  the  Later  low,  is  i s  on a  Andrewartha  individual.  cluster  behaviour  of  i t s e l f  average  this  to  consider As  individual  of  this  extremely  population  the  of  doing.  the  plant. in  may  essential  as  clusters  consequences  the  food  moths,  behaviour  from  and  the  proportions  on  their  host  plants.  Sometimes, l a i d ,  the  larvae  as  a  consequence  surviving  from  of  those  the  large  eggs  number  w i l l  of  eggs  completely  129  defoliate plants. the  a  plant,  and  This  point,  when  food  plant.  available,  Monro  (1967)  relationship Berg,  and  I  be  the c a l l  proposed  between  their  w i l l  host  the plant,  forced  to  disperse  to  new  food  needs  of  the  the  point  of  overloading  the  term  larvae  to  of  larvae  describe  host  exceed for  a  the  similar  Cactoblastis  cactorum  Opuntia.  Results I same  assumed  leaf,  of  the  on  this  The  had  of  means  only  one  of  only 25% o f  plants  were  clusters,  or  to  the  each  cluster.  seemed  a  that  clusters  in  lower  rate  plants  clusters.  were  without  more  had  two  each  or  more  clusters,  and  a  few  clusters.  distribution  (Table  This  on  'short'  excluded  locations  than  plants  f i r s t  significantly clumped  since  compared  oviposition  a l l  based  assumption I  the  was  analysed.  At  are  location  Poisson of  were  when  on  regardless  analyses  justifiable  plants  clusters  females,  The  identical  differed  both,  different  the  and  separate  by  corresponding  the  than  two  laid  almost  ' t a l l '  A deviation either,  were  the  distributions distributions,  in  This  cluster  with  Because  to  eggs  of  there  been  were  distribution  plants, 10%  i f  assumption.  compared 14).  they  number  cluster with  that  the  actual  from  expected. plants  only  random Thus  received  more more  expected. from of  a  the  Poisson  results  following  from  a  assumptions:  failure 1.  to  Clusters  meet are  130  TABLE  14  Distribution of T y r i a egg c l u s t e r s per p l a n t . The o b s e r v e ! d i s t r i b u t i o n at each compared with the corresponding distribution. Only •tall* plants and c l u s t e r s are considered.  No. of Clusters /plant  TOP  Hean Density (clusters /plant) Chi P  Obs. 123 27 7 2 3 0 1 0  0 1 2 3 4 5 6 7-  2  (df)  FIELD  P. PYLON  Exp.  Obs.  1 0 9 . 39 4 3 . 62 8. 69 1. 15 0 . 11 0 . 00 0 . 00 0. 00  69 40 9 5 2 2 0 0  1  P.PYLON  Exp. 62. 44. 15. 3. 0. 0. 0. 0.  Obs.  2  Exp.  194 1 8 3 . 82 36 4 9 . 01 6 6 . 53 3 0 . 58 0 0. 03 0 0. 00 0 0 . 00 1 0. 00  03 44 92 80 68 09 01 00  0. 399  0. 717  0.267  8. 96(1)  8. 50(2)  4.50  <.  <.  <. 0 5  01  S. jacobaea location is Poisson their egg  05  For a l l l o c a t i o n s , c l u s t e r s are e x p e c t e d f o r random o v i p o s i t i o n .  \  more  LAKESIDE Obs.  Exp.  210 2 0 2 . 9 0 27 37.42 4 3. 45 2 0.21 1 0.00 0 0.00 0 0.00 0 0.00 0 . 184  (1)  6 . 2 0 (1) <.05  clumped  than  131  laid  independently  •attractive' oviposition probably  as  i s  met.  one  of  clusters  those  the  above  The  For  number  The  c h i  laid the  example,  of  leaves  plants  plants  there  tests,  2  shift  indicated small  between  of  the  that  plants. To  distribution assumes leaves  out  plants on  them,  plants  a  measure 255? o f  but  the  how  were second  and  laid  leaves  in  in  assumption size  the  22.  For  based  on  distributions. the  plants  equally  left  than  on  wrong.  d i stri b u ti on .  are  leaves, on  Figure  is  to  should  of  influenced  proportion  -  clusters.  towards large  the  leaves  plotted  expected  on  should  we  disagreement,  plant  second  -  the  in  10  number  was  plant plants  plants  egg  to  of  size  have  do but  preferences  size  presented  distributions  much a  the  clusters  are  different, that  a l l  6),  make  given  plant  according  observed  clusters  calculated are  of  significant  the  Therefore  I  the  expected  more  find  those  results  was  size  of  grouped  The  no  females  Size  may  abundance  d i s t r i b u t i o n of  assumption.  that  a  of  is  analysis.  showed  25%  assumption  (Table  of  carry  were  expected  locations  to  factor  equally on  assumption,  plants  the  a l l  experiments  f i r s t  plants  i f  as  in  moths  on  second  are  The  the  'short'  included  If  Plants  sites.  the  possible  reflect  expect  a l l  not  2.  that  small,  attractive.  population. using  showed  regards  against  therefore  simply  and  As  were  number  another;  oviposition  plants  unequally  one  behaviour  discriminate these  of  cluster  This the  model  number  attractive  of as  132  oviposition  sites.  given  was  stem  leaf leaves,  of  a  certain  times the  the  The size  of  model  distribution  expected  number  a  product of  per  of  of:  a  cluster leaves  were  The  laid of  cluster  on  any  than  for  in  the  used  clusters  abundance  finding  plant.  a  rosette  probabilities  results  (at  Lakeside. although  would  complex  of  related clumps,  density.  for  of  on  results  of  a l l  on  plants  the a  class,  leaf,  are  the  larger  and  times  given  in  greater  But  of  when  s t i l l  is  remaining c h i  exception  the  2  of  discrepancies, received  unlikely  that  a  d i s t r i b u t i o n ,  factors  probably  more single for-  a  influences  sites.  density  have  areas  plants  interested  distribution  the  to  i t  observed  significant  pattern  abiotic  plant  selection  with  the  the  give  observed  oviposition  namely  to  Indeed, the  of  Yet  locations,  the  that  one.  clear  particularly  on  description  enough  no  biotic  factors,  distinguish  f i r s t  'explain'  choice  clumps  thought  the  expected.  both  was  better  is  several than  a  large  p=0.05)  factor  I  are  There  clusters  moth's  is  than  discrepancies  plant  for  separate  was  leaves  finding  23.  This  a  so  of  different  probability  number  Figure  probability  s l i g h t l y  and  calculations.  The  of  biomass would  high  plant  the  numbers  in and  any the  effect size  clusters.  Since,  than  single  do  favour  density of  moths from  clusters  of  of on  plant average,  plants, that  areas per  two  I  could of  plant  low was  133  FIGURE  22  The observed and expected distribution c l u s t e r s on t a l l S. j a c o b a e a p l a n t s when a are assumed to be equally attractive. g r o u p e d a c c o r d i n g t o t h e number o f leaves Observed distribution is given in sol expected d i s t r i b u t i o n i n dashed lines.  s of egg l l plants Plants are counted. id l i n e s ;  N u m b e r of C l u s t e r s O  o  L_  u  Laid ro O L  o .1  I I  I I I  L__J  •H L.J  z c  3 cr  O  CD  LJ  I I  CD CD < CD  cn  cn  o  1i r-  CD PT CD W  Cl  CD  TJ O  o  CD  CD  i  "U  "II  i  O  ro eeei.  -i  o  o 31 CD  Q.  FIGUfiE  23  The observed and expected distributions of egg clusters on t a l l S. j a c o b a e a p l a n t s when a l l leaves a r e assumed t o be equally attractive. Plants are grouped according t o t h e number of l e a v e s c o u n t e d . Actual distribution is given by solid lines; e x p e c t e d d i s t r i b u t i o n by dashed lines.  Numberof o  o  CI u s te r s L a i d ro o o o I  o  1  c  3  cr  1 1 1  CD  1 1  1 1  i  CD  <  CD  co  _i  ai  -r i  1  i  H  cu  •h.  n  O J  05  o  TJ o  c/>  CD  CD  11 —  e pei  01  =J -n  A*  H .1 O  o •a  CD  135  plotted,  either  against  the  preference trend per  number  towards  is  in  the  plant  as  plant  The  lack  oviposit,  at  so,  of  clumps  eggs  as  area,  of  then  they  S.  Moths  the  equivalent  on  clump  Field  lower  as  plant  rarely  clumps.  If  central  points  in  Fig.  horizontal  line.  plants 25  I  lay  high  same  spaced-out  fact  the  clusters  on  that the  central  moths  not be  if  number  of  Field  into  away why  cluster 25) .  sunlight;  plants  of  scattered seek  a  before  (Fig.  the  when  an  explored  'protected',  neither  density  density;  larger in  and  exploration  distance  are  were  any  suggest  f l y ,  flew  they  become  presumably  plant  such  plants.  moths  without  some  clumps  that  or  no  fewer  jacobaea the  also  clumps  would  S.  plant  leaves  in  conclude  of  of  flew  eggs  25),  moths  occasionally  then  on  that  to  observations  oviposit  they  areas  while  24),  In  towards  Frequently  host  (Fig.  evident.  receive  number  a  (Fig.  2  larger.  respect  idea.  m  clumps  suggests  would  this  plants;  jacobaea  plant the  around  a  out,  nor  searching  for  sites.  The  rest  are  on  proportions  become  with  per  direction,  correlation  therefore  that  clumps  oviposited  oviposition  was  an  generally  avoid,  factor  reverse  support  was  in  jacobaea  oviposited;  density  either  density  plants  S.  surrounding  large  plant  of  random  do  observations  of  against  of  this  overloaded of  the  section plants,  looks and  at at  f o l l o w i n g : "the  the the  proportions effects  presence  of  on  plant  of  eggs these  clumps,  136  FIGURE  24  Relationship between t h e number p l a n t and p l a n t d e n s i t y . None o f s i g n i f i c a n t at p = 0.05.  of c l u s t e r s on the r values  each are  2.01  °  Power  Pylon  Power  1  2  r =-0.248  r=-0.305  1.2-  Pylon  0.8o  c  -  0_  o  o  0.4  o  o  0  -O  o  o  o r  T  _o O  o o  - r  T  r  o  o o  -i  r  i— CO  CD  Top  -t—-  => 0.6H  Lakeside  Field  r = -0.4l9  r = -0.034  O  0.4o  0.2  o  o  o  o  0  0  —0  20  9  1  1  40  -r  60 Plants  0 Per  o  o  w  ° -i  Met re'  o-r  20  O  o  o 1—o  40 r  r  60 CO  137  FIGURE  25  Relationship between t h e number of p l a n t and the s i z e o f p l a n t c l u m p s . values are s i g n i f i c a n t at p = 0.05.  clusters None of  on each the r  137a  1.0Power Pylon 2  Power Pylon 1  0.8-  r =-0.325  r =-0.109  0.61  0.4-  o  ro 0.2-  i  w ^  CO  O  20  10  °  0  o  oo  o  w  o  10  0  20 42  1.01 1  Lakeside  Top Field r = 0.061  0.8-  r =- 0 . 6 0 8  0.6-  0.4-  0.2-  o-0  o  o  10  20  0  "° io" —0  Number of P l a n t s in C l u m p s  20  138  and  the  of  the  is  the  that to  age,  density,  larvae.  have  complete  location number  of  the  end  only  5%  data  for  each  the  food  on  A l l  the  is  distribution  pattern  on  overloaded  plants*  of  surviving  larvae  their  original  clusters  following  cluster  of  the  used,  host  l a i d  results,  and  rather  Pylon  and  (c)  their  clump.  The  plant  clumps  clumps  included.  value  plant  in  the  than  each actual  a  mean  overloading be  seen  by  f i e l d  situation  a  noticeable plants  would  observed  be  amount  higher  of  more  19% compared  out,  with  overloading  proportions  of  when  recorded  for  plant  including  and  the  In  only  a  (b),  the  the  of  (c)  accurately,  spaced  were  or  with  other  clump.  part  excluding  to  the from  with  eggs  (a)  to  average  plant  were  difference  on  exclude  contact  comparison  are  development  we  the  with  they  that  in  i f  whole  comparing  were  of  is  that  i f  point  in  plants  even  eggs  requirements  food,  5%  of  of  contrast,  important  i f  eggs  The  on  this of  of  food  plants  biomass  weight  To  short  more  make  Hence  the  be  This  the by  can  the  overloaded  1.  larval  instar.  will  own  effect  The  describes  proportion  consider  fourth  assigned  (a)  (d) .  the  cluster-carrying  were  assigned  we  larvae  Power  Columns  i f  the  (d);  l e v e l .  estimates  plants of  Column  for  in  eggs  proportion  insufficient  in  15  overloaded  plant  'the  of  and  size.  Table  plants  for  included  eggs  rate,  proportion  development*.  are  cluster  with  'The  abbreviation  would  survival  and  (c)  with  (d)  shows  that  overloading proportion  estimate  plant  of  clumps  Power  of 6%  were  Pylon  1  139  TABLE  15  Proportion of eggs estimated to be p l a n t s when f o o d r e q u i r e m e n t s to the fourth' i n s t a r are considered.  CLUSTERS POOLED PER PLANT  CLUSTERS TREATED SEPARATELY Host Plant Alone (a)  on o v e r l o a d e d end of the  Host Within Clump (b)  Host Plant Alone (c)  Host Within Clump (d)  Location  Surv  Top Field  0.101 0.153  .02 .09  .02 .02  .02 .20  .02 .05  1  2  3  Power Pylon  1  0.104 0 . 153  .09 .20  .05 . 12  .23 .42  . 19 .26  Power Pylon  2  0 . 104 0 . 153  .10 . 20  .02 .04  .15 .22  .07 .07  0 . 104 0 . 153  .16 .23  .04 .06  .24 .32  .04 . 12  Lakeside  •-Survival  rates  are  derived  in  Appendix  1.  Plants are assessed i n d i v i d u a l l y ; other contact are ignored. Food requirements cluster are determined from: (Eggs in (Survival R a t e ) x (Food Reguired/Larva to Fourth Instar). 2  plants in for each Cluster)x end of  If a plant is in contact with other plants ( r o s e t t e s and/or stems) the biomass of that clump is summed a n d c o m p a r e d w i t h t h e f o o d r e q u i r e d . 3  C l u s t e r s i z e s f o r each are : Top Field 118 ( 5 0 5 4 ) ; P o w e r P y l o n 49 (2163) .  location (with 88(2242); Power 2 73 ( 3 4 9 1 ) ;  egg totals) Pylon 1 Lakeside -  140  reflect  the  high  Tables Table to on  15,  the  rate 2).  16  of  lower of  the  g  are  the  per  do plants  locations,  and  can  of  larva  are  naturally  seen.  clusters;  density;  3.  The  growth  change  larval  examined  I  location plants eggs  as on  effect i f  in  of  the  of  16 a  cluster  on  that  in  Column  (b)  Therefore clusters  is the  is  to  are:  1.  and  34%, effect  almost  16  the  the The  are  (see  Appendix of  proportions  on  this  between  instar.  and  influence  in  four  or  mean  plant  within  of  contagious,  in  the  quantity  in  change  based  whereas  17  to  considered  larger  both  plants  distribution  17.  In  clump(where  plant.  Table a  manner  are  Table  higher  The  Columns  spaced  evenly  17  patchy  are  ire  and  similar  14).  patchy cluster  clumps;  4.  The  can  be  rates.  plant  clusters  in  (Table  larva,  instars,  some  compare  Tables  a  of  in  per  much  a  larvae  consume  2.  survival  we  part  16  These  of  The  g  considerably  Tables  in  of  used  larvae  distribution  in  is  location  Values  0.440  earlier  from be  instar.  vary  that  needs  the  proportions  at  constructed  food  rate  fifth-instar  overloaded  factors  density  f i f t h  feeding  than  These  17  that  0.744  Because  food  and  except end  the  cluster  added by  The  (b)  both  of  and  these  (d)  appropriate); together,  but  considering average  (b)  each  as  of  contagious  the  proportion  i t  we  (d)  in  in  the  in  proportion (d)  within  estimates  whereas  double  clusters  of rises  a l l we  eggs  treat the  imagine  the  only  overloading to  distribution of  each  that  63%. of are  111  TABLE Proportion p l a n t s when feeding are  16  of eggs estimated food requirements to 0.440 g per larva.  CLUSTERS TREATED SEPARATELY i  Host Plant Alone (a)  t o be on the end  overloaded of larval  CLUSTERS POOLED PER PLANT  Host Within Clump (b)  Host Plant Alone (c)  Host Within Clump (d)  Location  Surv  Top Field  0 .. 0 9 3 0 ., 1 3 8  .40 .60  .24 .40  .67 .88  .55 .75  Power Pylon,  0 .. 0 9 3 0 ., 1 3 8  .56 .68  .31 .45  .78 .91  .56 .86  Power Pylon  0 ,. 0 9 3 0 ., 138  .45 .60  .26 .37  .65 .81  .51 .62  0 .. 0 9 3 0 ., 0 9 3  .52 .73  .29 .43  .77 .83  .54 .64  2  Lakeside  A l l  footnotes  1  are  the  2  same  3  as  for  Table  15  TABLE Proportion p l a n t s when feeding are  17  of eggs estimated food requirements to 0.744 g per larva.  overloaded of larval  C L U S T E R S POOLED PER PLANT  CLUSTERS TREATED SEPARATELY  Plant Alone (a)  t o be on the end  Host Host Within Clump (b)  Host Plant Alone (c)  HOSt Within Clump  Location  Surv*  Top Field  0.093 0 . 138  .71 .87  .42 .56  .92 .97  . 80 .94  2  3  Power Pylon  1  0.093 0.138  .74 .89  .49 .59  .94 .99  .87 .99  Power Pylon  2  0.093 0 . 138  .63 .84  .42 .56  .83 .95  .63 .68  0.093 0 . 138  .76 .82  .45 .61  .85 .87  .69 .69  Lakeside  All  footnotes  are  the  same  as  for  Table  15  143  on  overloaded  cluster the  density  observed  Lakeside, plants  plants. at  some  differences,  where  even  Part  i f  there  a l l  the  of  this  sites. since  increase  Yet the  would  this same  is  due  to  does  not  explain  a l l  is  evident  in  effect  have  been  a  had  been  spaced  clusters  the  surplus  high  of  large  one  to  a  plant. The cluster  effect  of  density,  can  proportions survival have  no  the  a  change  since  at  Power  a l l  the  were  overloaded  plants  Lakeside  the  Higher  survival  suggests  the  different Power  and  1  rate  plants  the  were  the  80%,  may  because  this  dropped  l i e I  in  closer of  to  their  more  to  food the  each  being  of  rapidly  in  cluster eggs  Why  which  in  Top  overloaded  Increasing  density.  of  excess  plants  cluster  on  at  density the Top  and  is  this rate?  in  turn  food  in  Field  and  the  low  than  were  survival Field  on  2  survival  consumption,  that  eggs  Pylon  63%.  higher  margin  At  the  proportion  around  to  other.  cluster  Power  0.093  overloaded  of  where  at  the  suggest  locations.  margin  average  at  5%  Field,  whereas  greater  much  other  Top  apparent  means  answer  survival  eliminated  was  locations.  Pylon  at  1  on  mean  the  appears  eggs of  mean  overload  At  proportion with  in  the  locations  within  correlated  change  locations.  of  the  the  compare  between  are  however,  is  only  we  between  values  proportion  effect  i f  density  highest,  density  factor,  proportions  rate  Pylon  densities  examined  in  the  plants  second  16 (d)  on  survival  overloaded Thus  Table  effect  0.138  be  in  rate  plants,  the  and  rate Power  144  Pylon  1 than  in  i s  consistent  the  higher  larval in  with  feeding  survival  Table  high  Power  The  two  contagion  of  the rate  since  when  plants  carrying  1  -  2  we  These  -  The  third  the  fourth  the  f i f t h  or  have instar;  instar,  i s  i.e.  When  treat  plants  we  treat  are  Top  as  Field  -  on  the  at  the  and  the of  and  hence  of  This  effect  is  that  with  for  clusters  Hence  amount  clusters along  only  density  density.  0.57  the  rates.  contagion  follows  (0.184  16(d)  effect  clusters  where  consumption.  cluster  of  17 ( d ) ,  increasing  survival  cluster  of  plants  affecting large how  plant  without as  eggs as  they  part on  the  feeding  predictably  supply  proportion  of  as  Table  combined  more  0.40  the  seen  food  the  -  in  explanation  Table  food  far,  proportion  factor  larger we  the  in  effect  both  so  This  are  the  the  per  (0.399);  on  cluster different  plant);  Power  Power  Pylon  .  plants  We  at  with  (0.267);  (0.717)  noted  a  data  same  amount  proportions  0.56  clumps.  have  the  Lakeside  overloaded  we  occurs  two  Lakeside.  greater  discussed  l i s t  0.44  the  means  increases  evident  Pylon  has  effect now  2 and  comparable  i t  clusters,  overloading,  locations:  rate  factors  overloading,  density.  the  rate;  17(d)  survival  Pylon  units  clumps  clumps  affected  have  a  the  for  a  clump  overloaded from  one  larvae  (Tables  plants  by  is  another  eggs  by  the  similar  larvae  need  of  created  benefit  of  separated  proportion  on  plant  data  for  effect  on  creating  a  to  disperse.  16(d), lower  17(d))  than  (Tables  16  when (c),  145  17(c)).  The  considered and  (b)),  had  result  is  the  independently which  adequate  suggests food  same ' e v e n  of  one  that  only  when  another  some  (compare  larvae  because  the  clusters  on  are  Columns  small  rosettes  were  proportion  of  (a)  rosettes part  of  a  clump) . The eggs  is  f i n a l the  factor  larval  discussed  in  larvae  greater  by  the  the  van  der  weijden  impact  run  of  a l l  and  on  food.  how  This  is  higher  greater  i s  has  the on  the  same  worth  noting  evident  of  9%  larvae  in  both  by  sedentary  starvation.  in  ' to  Table  with  a  my s t u d y  14%, were  16  young  resource  point  that  been  of  food  made  f i f t h - i n s t a r  already  the  chance  from  overloaded  survival  the  survival,  many  which  pressure  has It  in  the  the  the  (1971)  increase  marked  in  be  example.  small  out  w i l l  the  rate,  Clearly,  instar  hypothetical f a i r l y  survival  part.  f i f t h  influencing  and  a  had  a  l i k e l y  to  Table  17  larvae  of  locations.  DISCUSSION The their  successful  host  plants  oviposition that  is  partly  determined  behaviour  of  the  species  of  Lepidoptera  several  unsuitable  exploitation  objects  reaching  a  host,  correct  choice  even of  and  that  when an  host  adult.  many  by  the  Dethier  site  larvae  were  appropriate  (1959,a)  deposited  young  plants  oviposition  insect  eggs died  abundant.  becomes  found on  before The  particularly  146  important  for  patchily  distributed  became §*  clear  a  that  JS22baea;  However,  such  other  biomass,  survival plant,  of  the  larvae  and  the  These  guestion  Part  laying i t s  in  eggs  host are  to  they  must  this  aspect  have act of  The  amount  Results  from  S»  jacobaea  cluster  in  a  were  big  that  survived  from  15%  of  plants  classified  as  a  and  of  or  more  females  egg  distribution help  the  after  is  size  1971  to  95%  to  support  average clusters  overloaded.  in  Since  of  on  had only  the  same  within  local  the  on  I  will  size  size  value  is  the  plants.  populations with  an  fifth-instar  the  of  discuss  jacobaea  remaining  insufficient half  of  individual.  plants  The  of  traits  adaptive  four  the  focal  strategy  cluster S.  the  cluster.  the  population  the  the  individual  study  females, on  manner.  to  at  distribution  on  constraint  looked  behavioural  outlining  be  to  Tjjria's  and  effect  respect  on  lay  can  relative  answer  i n t r i n s i c  with  enough  with  individual  on  objects.  I  laid  by  given  85%  II  eggs  adaptive  upper  other  Part  eggs  "How  food  that  i t  oviposited  of  of  results  the  in  density-dependent  f i e l d  showed  number  regulatory  obvious of  well,  these  behaviour  most  limited  any  the  oviposition  as  relationships  If  work  behaviour  two  clusters,  f i e l d  oviposition  spacing  II,  plant?"  Tyria  of  in  consistently  a  of  pattern  populations.  my  has  on  the  when  During  that  ovipositing  levels as:  Tyria  seen  adaptiveness  at  like  plant.  females  was  relationships  plant  species  host  Tyria  none  the  examined  monophagous  food  total  of egg  larvae 5%  and  number  to were of  147  plants  in  cluster  this  result  plants  over  small  shown  these  in  Fig.  selection  was  rosettes  were  plants  below  were  The  not  carrying  egg  up  clump.  When  just  with  clumps  adaptive  value  on  units;  S.  defoliation  I from  average  When  A  plants  over  former;  many  vegetation  these on  last  'short'  stems  and  paragraph  also  touched plants  for  plant the  dropped  turn,  a  the  a l l a  the plant  cluster  was  of  85-95%  when  25-65%.  Hence  the  sizes  depended,  in  was  as  with  cluster  vegetatively  plants  increased  to  figure  to  those  dispersal;  referred  needs,  in I)  that  each  observed  {Part  the  need  of  form,  that  any,  biomass  growing  Tyria  in  the  food  plant  different.  surrounding  considered,  growth by  i f  is  vegetation.  the  rates  large  host  surrounding  infreguently.  were  the  the  of  average  preference  stemmed  height  an  choose  This  in  for  the  groups  larval  of  estimated the  the  jacobaea  this  of  without  such  the are  plants  'plants'  These  moths  affected  oviposition  plants,  larvae  making  compared  to  that  greater  the  clusters.  plants  part,  level  support  oviposition.  s i g n i f i c a n t l y  surrounding  plant  the  to  female  moths  the  reference  for  by  relatively  included  supply  that  of  to  excluded,  enough  factor  height  due  on  large  for  One  the  laid  were  rosettes  plants  preference  rosettes  were  were  indicates  23.  was  significant  and  areas  compact often  a  in  feeding result  of  .  while  the  cluster  did  food not  required  exceed  the  by biomass  survivors of  most  148  §*  jacobaea  small, close  since to  margin size,  plants,  food  the  biomass  w i l l  depend  and  factors  the  the  larval  tended  defoliated  1971  compared  of  starvation  from  nevertheless biomass  on  butterfly  on  and  i t s  how  plant.  female  for  jacobaea  plants  one from  cluster f i e l d  maturation.  in on  of  each  the  Aster  given  plant. Scud,  of  her  of  and  moths  way  laid  M i l l .  of  sites,  had  smaller  the  Field  were larvae but  available  contrast,  type  in  because  of  20  the  to  the  400 food  1959b).  clearly  she  Females  plants  exceeded  the  way  two  that  (Dethier  of  depend  plant  she  distributes  eggs  accurately  chose  discriminated  against  and on  from  data  usually  of  size  on  f i r s t  food,  clusters  Evidence  and  plant  clusters  of  most  plants,  size,  Top  concluded  cluster  the  large  plant.  I  short  eggs;  this  were  When  was  of  locations  invariably  umbellatus  size  Field  thus  other  By  cluster  similarly  u t i l i z e  oviposition  observations Female  be  population. as  in  other  larvae  lays  and  probably  the  Top  year.  not  advantages  favour a  1970,  egg  cluster  area In  was  The  in  study  previous  oviposition plant  plants  of  plant.  than  probably  moth  the  small  1971  food  average  locations;  h a r r i s i i  needs  selective  the  chooses within  the  host  The on  in  my  and  particular  Melitea  the  synchrony.  would  would  their  In  in  the  clusters  by  fluctuations  other  smaller  surplus  average  1969  independently  most  eggs,  on  with  were  treated  the  change  clusters larval  of  in  of  required  survival.  to  been  margin  probably  this  oviposited  last  on  the  in  the  laid  only  point  came  rate  of  egg  afternoon,  1 49  and  took  l e f t  1-3  them  hr  to  lay  insufficient  temperature  f e l l  and  k i l l e d  oviposition  the  to  in  the  a  f u l l  lay  to  mature  plant  is  survival and  her  apparent  already  have  laboratory randomly already  of  these  proportion  of  four  locations  more  clumped  overloading of  females  doing  so  three  on  of  the  plants plants  clusters the  16  than  lay  tended  leaves.  on  Clumping  on to  large be  two  overloaded  was  of  plant,  to  day  of  larval  lower  with  clusters  negated  i f  plants  that  was  two  the or  In  a  clusters that  this  also  partly  hence  shown  36  were  lack  of  clusters,  and  density  further  plants;  as  oviposit.  more  plants  caused  a  different  mother*  of  or  As  which  a  clusters  result  overloaded.  unlikely  that  against  decides  carried  mature  plant.  Tyria a  were  manipulation  distributed  As  random,  were  on  the  finished  required  'perfect  she  other  often  per  per  no  moths  to  they  showed  discriminate when  fewer  cluster  cluster  i s  distribution  effect. to  them  10  experimental  clusters  to  were  each  females had  or  usually  before  they  moths  plants  one  cluster  that  since  for  female  i n a b i l i t y  had  indicated  which  Thirty  after  Laying  with  second  they  stemmed  respect  some  discrimination many  and  experiment  on  a  cluster,  sluggish.  found  eggs.  Tyria  eggs  with  I  adaptive,  with  the  became  which  highest  lowest  lay  immediately  many  rosettes  However, by  cluster  was  to  immediately  abdomen,  that  on  time  f i e l d .  presumably  clusters  two,  in  average-sized  they  c a p t u r e d ' and  eggs  an  rose, rose.  In  the a l l  s i g n i f i c a n t l y increased by  the  tendency  advantages more  the  of  females  150  oviposited choice  of  If  on  plants we  overloaded than  are  how  this  the  same by  larvae  are  on  clumped  population  females  assume, plants  sufficient larvae  to  to  be a  of  marked  be  needs  of  plants  w i l l  the  that  moth  the  a  and  cluster  at  larvae  very  on  clumping  of  paper  acted  Monro balance He  egg  of  total or  clusters  a  a  few  between  effect  is  the  a b i l i t y  of  w i l l  w i l l  when  no  also  creates  within  plants  occurs  each  w i l l  s t i l l  the  total  available,  some  larvae. in  (1967)  populations hypothesised  mechanism.  Cactoblastis when  leave  clusters  Nicholson's  that  more  the  I  biomass  Monro  of  directly rate  densities  even  rate  III.  egg  regulatory  challenged  proposed  Part  describe  be  on  on  adults  the  growth  densities,  cactorum. as  w i l l  Hence  larval  few,  can  distributions  densities  them  Cactoblastis  (Op_untia).  clumping  we  affects  depend  clumped  the  the  larvae  become  Whether  plants.  high  exceed  have  w i l l  of  to  the of  The  action  densities.  host  affect  that  then  clusters  reduce  heterogeneity low  'hide-and-seek'  pear  III.  egg-clumping  stimulating  new  survive  plants,  i t s  numbers  regulatory  s t i l l  A similar  low  being,  to  of  that  studied.  time  w i l l  at  to  Part  At  the  l i k e l y  consequence  spatial  overloaded,  of  than  the  in  population.  less  s t a b i l i z e  other  examined  the  Clearly  factors  not  for  and  disperse  discussion One  high  were  distribution  growth.  at  Other  non-overloaded  density-dependent severely  plant.  (1947) and  In  a  view  of  prickly  Cactoblastis  was  151  abundant by  i t  avoided.the  sparing  some  total  plants  overloaded  other  plants,  eggs.  He  found  that  high  density  rates  of  larvae  were  from and  unable  thus  and  were to  of  attack.  egg-sticks  populations,  increase  destruction  At  wasted (or  that,  a  as  far,  prickly  the  same  a  were  of  result,  they  i t i t s  clumped  in  effective  reduced.  and  pear  time  proportion  clusters)  s i g n i f i c a n t l y  wander  the  Dispersing  suffered  high  mortality. Monro of  described  comparisons  the  t e l l  (cactus)  from  or  influenced clumping might  have  as  a  seems  benefits had  not  resource."  plant the  a  factor  number  in  different  to  be  of  Tyria.  states, an  If  could  from  discriminate  against  Yet  selection  would  the  he  put Part  II  at  high  large  about  4).  one  number  of  per  plants  the  unable  plant  to  population in  namely, to  Monro  of  behaviour suggest  why 'egg-  by  depleting  a  different  "Females  have  why  was  evolution  "...opportunistic  density;  host  behaviour  was  appear  and  influencing  a l t r u i s t i c  results,  basis  Cactoblastjs  question  would  the  of  the  this  Table  egg-clumping  for  endanger  clusters  particularly  "The  the plant  leaves  selecting  example  group."  been  One  was  in  on  per  (his  variation  conclusion  perspective  advantage,  whether  a  He  clumped  egg-sticks  of  the  which  of  consequence  behaviour.  spreaders' the  per  being  distributions  selection  reached  Cactoblastis  there  data  as  number  Clearly  host  eggs  this  which  his  not.  the  Poisson  segments  selection  of  between  corresponding  cannot  egg-sticks  a  that  selective  haven't  they  152  evolved?" I  can  employ  to  visualize  detect  overloading a l l  the  a  on  time-consuming, which  Alternatively, that  could  This  be  also  leaves females  would  plus  an  of  a  mark  other  reguire  would  be  the  might  to  avoid  underside  this  be  of  extremely  some  way  of  already  searched.  with  pheromone  eggs  females  female  able  need  had  their  the  appropriate  so  would  herself  might  Tyria  search  only  female  a  and  could  Not  she  by  which  eggs  female  plant.  detected  tactic  pheromone  A  each  but  tactics  presence  plant.  leaves  knowing  the  two  landing  development  a  on  that  of  a  reception  system  and  l i k e l y  evolve  in  plant. suitable  behavioral  response. These  tactics  plant  system  than  small  enough  to  capacity these  tactics  (Lloyd Some tend  to  1940;  1948);  to  tactic  oviposits  on  Clearly,  less  parasite-host  rapidly  Ullyett  f l i e s  their  eggs  large  f r u i t s  tansy  in  and  1953);  the  such  ragwort  also  there f r u i t as  is  l i t t l e  a  a  Dacus  u t i l i z e eggs 1971).  f r u i t s  (Boyce  apples,  larger  and  and  also  (Martin 1934).  evidence tyroni,  is  fixed  their  olives  walnuts  provides  of  small  and  peaches,  host  G r i f f i t h s  in  f l y ,  the  Hymenoptera  in  as  herbivore-  has  wastage  oviposit  a  where  1961;  uniformly,  (1969),  operating  and  Wilson  that  (Hafliger  Pritchard  system,  Certain  overloading  1949a,b;  f r u i t  to  searched  parasites.  prevent  cherries to  a  support  disperse  According this  in  be  tephritid to  are  of which  pears.  more  153  variable  food  supply  insects.  While  d i f f i c u l t , t h e pressure able  for  to  energy  by  merely  do  plant  size  v a r i a b l i t i y  in  discriminating  support  Freguently  than  the  therefore, searching  searching  for  host  plants.  selective  advantage  make  evolution  of  similar  argument  •opportunistic A the  third,  rather  disadvantages  that  example,  laying  This a  being  explored  with  model  the  and For  ease  hypothetical another,  clusters at  top  is  right  is  a  of  I  cluster random. Fig.  size  proposed  tactic, from  reduce  (Fig. from  assume  the  be  wasting  rather  the  than  absence  of  appears  a to  Perhaps  absence  be  the  failure  cluster  to  are  that  equal  differs total  size,  a of  reduce to  so  three  that,  clusters  disadvantages  the  nature  presented a l l  size and  to  overloading,  26);  i t  constant,  but  be  would  and  size  w i l l  Cactoblastis.  advantages  of  more  clusters.  unlikely.  explain  respect  I  is  Cluster 26),  This  or  drew  are  would  two  model  calculation  population  of  with  female  plants  support The  simple  conclusions  to  more  host  result  could  clusters,  in  host-  selection  plants  or  system  different  overloaded.  smaller  two  to  or  the  discriminators  advanced  tactic  plant  for  pheromone  be  and  without  one  a  egg-spreaders'  discriminate. for  could  from  Tyria-free  lessens  sometimes  discriminating  for  fruits  host-searching  size  females;  larvae a  orchard  makes plant  persistent the  either  the  of  the  below. in  separate  of  curves eggs  a  from  distribution  between number  were  plants  and  of  of  (shown laid  by  1 54  each  female  small  is  clusters  of  each  plant  i s  also  set  size  and  that  held  distributed overloaded This  at  an  This  plants  average  at  i s  and  The  the  'normal'  parallels  cluster  lay  the  most  a l l  plants,  then  a l l  eggs  to  as  the  size  result,  i f  referred  cluster  observed  Thus  than  density  cluster  utilized  greater  many  between  plant.  densities  from  overload  correspondence  roughly  between  females  clusters.  eggs,  average  evenly  Therefore  large  40  eggs.  the  density  few  biomass  from  of  a  set  40  plant  larvae  biomass  to  i s  at  constant.  40  the  clusters would  eggs  Overload  of  be  per  Density  are on  plant. in  Fig.  26. The values  curves for  a  the  mean  are  on  the  same  mean  24  eggs  per  (those  given  number  less  of  eggs  per  plants the  cluster. half  they  clusters  a  the  in  is  20,  eggs rises  to  not  3%  high  low,  size)  are  chances  a  small,  ywhen  of  eggs  the  whereas  60%  as  small  at  with  clusters  advantageous, of  the  further  the  example,  cluster; as  point  with  For  is  female's  and  examines  only  per  density  overload  laying  one  density.  normal  decreases,  l i e s  4  figure When  i f  egg  plant  the  Near  or  with  reduce  plant.  advantage  understood  x-value,  density  than  as  overloaded  the  best  overloaded  insofar  small  are  laying  on  advantage rise  but  an of  in  density  large,  40-egg  clusters. The w i l l  be  explanation a  few  i s  large  as  follows.  clusters  At  any  (i.e.  a  given low  density mean  there  number  of  155  FIGURE  26  Predictions from a model of the p r o p o r t i o n of eggs on o v e r l o a d e d p l a n t s when c l u s t e r s i z e is changed. Clusters are l a i d at random. P l a n t s are assumed to be o f e q u a l s i z e a n d o v e r l o a d e d a t more t h a n 40 e g g s per plant (Overload Density). At low egg density s m a l l c l u s t e r s minimize the p r o p o r t i o n of overloaded eggs; at h i g h egg d e n s i t y the l a r g e s t c l u s t e r size minimizes the overloading.  155a  156  clusters/plant) w i l l of  be  more  Poisson  densities a  greater  more is  distribution  eggs  on  more  number  of  to  that  of  egg-sticks  there  plants  and  suggests  the  larvae  of  large  clusters,  of  the  decline  is  s i m p l i s t i c  A  f i r s t  to  a  distribution  introduce  increased  the  changing  the  incorporate  degree  of  cluster  into  she  step  the  would  and  If  have  spend  host plants.  presumably  lower  fecundity.  Given  that  smaller  clusters,  the i t  model i s  worth  as  more  size  This  suggests noting  an  even  at  which  point  destroyed. as  egg  This  a  clumped  by  reducing  in  some  of  its  would  be  a  function  which  real  effects  that  are  more  more  d i f f i c u l t  laid  4  time  and  extra  that  from  outbreak.  and  an  also  r e a l i s t i c  female far  the  minimized  well  an  places  conclusion  that  been  Other  a  selecting her  This  cactus  have  high  does  (1967),  of  have  very  than  clusters.  i t  might  (  At  clusters  unrealistic  plant  model. to  low.  plants  follows  clumping. size  skewness  small  size,  making of  greater  s t a b i l i z i n g effect  that  in  clusters  overloading,  would  a  large  suggested  cluster has  the  are  of  segment  universal  of  Monro  He  was  that  model  and  by  per  these  means  large  reached  assumptions.  flying  of  considerations.  magnitude  cluster  the  overloaded  distribution  u n t i l  The  consequence  even  distribution the  a  the  distribution  result  as  clusters;  when  similar  the  small  distributions  clumped  wastage  many  clumped  theoretical  a l l  or  eggs  advantage in  1971  per  energy  activity  in  the  to  in  would  laying actual  TABLE  18  D i s t r i b u t i o n of egg c l u s t e r s according to of eggs per c l u s t e r . D a t a a r e f r o m 1971 P o w e r P y l o n (1+2) and Lakeside.  Eggs/ Cluster  Number of Clusters  1-9 10-19 20-29 30-39 40-49 50-59 60-69 70-79 80-89 90-99 100-109 110-119 120-129 130 +  Mean  cluster  size  is  44  7 38 42 33 27 28 21 14 15 6 4 2 1 2  eggs.  the number samples in  158  distribution  of  proportion  clusters  that 30  year  and  such  of  50  as  early eggs  daily  weather  size;  advantage  of  a  of  survival  (Table  cluster  avoid  cluster  11).  overloading  less was I  plants  and  the 30  highest  have  work  variance  in  than  conditions  further large  sizes  eggs for  shown and  age  cluster  thereby  included (Table  clusters  that  could  in  f i e l d  a  high  18).  In  of  between  proximate  factors  of  female  examine size  as  increase  success.  i  the a  affect relative  strategy  to  reproductive  159  PART  III.  STRATEGY  FOR  PERSISTENCE:  THE  LARVAL  STAGE  INTRODUCTION One  consequence  clusters,  and  i s  larval  that  plant  within  larvae  of  an  w i l l  larval  heterogeneity T^ria  their  of  high will  larval  must  meet  (1971)  their  f u l l  less  than  their  consequence  the  plant o f f ,  and  finds  larva an  reproductively  defoliated  It important dispersers  that  i f  other  the as  plant  to  low  some  hand,  when  on  overloaded  food.  Within the  this  adults,  consumption a  of  consequence,  were  lighter  that  seemed  that  role  affecting  than  some  and  i t  had  larvae able  although  the  from  host-plant i f  were  weight,  •disperses  undefoliated speaking,  f i f t h - i n s t a r  requirements pupation  until  and  -  and  normal  plant  in  size,  found  food  pupae  a  prime  from  by  in  adult.  Meijden  Therefore  excess  eggs  clusters,  is  are  need  an  fecund.  larvae  have  pupal  these  the  their  as  at  many  On  created  fecundity  denied  plants.  and  their  density  densities,  maximize  der  laying  considerably  larval  s t i l l  to  pupate a  overloaded  very  vary  when  food  van were  on  T^ria  d i s t r i b u t i o n of  w i l l  Even  larvae  larvae  sufficient  clumped  area.  is  some  female  density  be  density  plants,  the  of  adults  a w i l l  to as less  defoliated be  'better  remained  on  the  pupation.  dispersal the  non-dispersers.  by  larvae  reproductive Certainly  might success the  play of  effect  an both  of  the  160  relative  food  clusters The  could  only  simple  aggression  der  while  f i f t h of  a  of  -  The form  of  reduce  For the with  f i f t h  two  importantly,  as  a  " . . . r e a d i l y  that  the  dispersed  ran  a  risk  the  process  of  from  an  a  viewed  of as  reasons  concentrated  F i r s t ,  shortages  this  than  larvae,  i s  of  in  the van  being  instar are  amount  together  conditions  l i k e l y  to  occur.  individual  which  to  dispersing  the  the  the  may,  while  however,  circumstances. on  measuring  i s  more  the  instead  by  in  larvae  brought  most  benefitting  certain  are  predicts  mechanism,  under I  Tyria  the  dispersing  gained  sections  which  regulatory  numbers  the  these  hypothesis  i s  a b i l i t y  advantages  outbreak  of  dispersal  of  results  for  plant."  the  the  although  ground.  examines  and  plants  consequence  host  larvae  were  disperse  occurs,  instar.  food  that  may  of  plants.  larvae  1971),  that  dispersal  to  Meijden  dispersal,  Larval  f a i l  Tyria  stimulating  an  as  stated  new  defoliated  larvae  m around  the  by  to  factors  which  acting  III  on  der  that  larvae 1-2  dispersed  left  van  distribution  the  under  also  of  he  showed  were  Part  plants,  larvae. the  radius  they  instar  new  suggest  patchy  dispersal  larvae  Specifically  (1971)  dispersal  find  did  the  larvae  on  1968;  f i f t h - i n s t a r  Meijden  Most  in  (1966)  within  eaten  that  Hawkes  by  i f  references  1935;  reasons.  caused  lessened  observations  Bornemissza  f i e l d  be  previous  (Cameron  other  shortage  frequently  earlier of  dispersal  instars.  remaining  in  faced More  gregarious  161  throughout  the  instar,  a  reasons  other  larval  change  than  DEVELOPMENT  Field  in  OF  period  behaviour immediate  AGGRESSIVE  Observations  Bornemissza  (1966)  Tyria  Bornemissza•s  the  literature,  describe  certain  particular behaviour  between  These  top  young in  i s of  in  From instar  aspects  of  groups  are  plant  and  on-plant are  differ  the  from  larval  During  mostly  leaving  the  discovered Second-  and  organized  for  feeding  movements most  mine  of  of  detailed I  shall  behaviour,  feed  paying  aggressive  these  early  instars  groups,  often  touching  aggregations  described  some  f i e l d  experiments  Bornemissza  were  larvae  i f  developing  actively  were  by  formed,  spaced  out  of  the  epidermis the  third-instar  dense  aggregations  tissue  upper  only  or  on  on  the  second-instar  disperse  the  development  feed  often  examined. the  the  larvae  leaf,  leaves.  loosely  not  the  larval  surface the  of  f i f t h  individuals.  First-instar surface  they  to  them  described  observations  since  attention  make  the  Experiments  mechanisms,  but  may  in  shortage, t  food  briefly  defence  in  which  antagonistic  BEHAVIOUR  and  periodicity, larvae.  become  intact.  lower  larvae  f l o r a l larvae one  lower  leaf  move  parts tend  to and  to  feed  another,  but  Bornemissza  concluded for  if  over  the  (1966).  that  early-  firstplant,  or then  162  local  groups  formed  and  coalesced  into  larger  groups  within  24  h. I  observed  instar top  no  larvae.  buds  and  such  While  young  young  feeding  larvae.  experiments  f i r s t - i n s t a r cm  x  10  showed that  In  another  larvae, the  one  larvae  although 4  to  days  a l l  the  but  contact  with  larvae The  viruses other for  after  experiment  I  on  two  feeding, one  larvae  larvae.  the  36  3  not  centre  of  area  within  3  on  1966).  Whether  on  the  the  were  24  h  plant.  top  flowers often did  most  leaves,  each  moult  and  f i r s t - i n s t a r  new  and  10  larvae  area  after to  sites,  during  (Bornemissza  moved  a h  f i r s t - i n s t a r  plants,  larvae  other  the  15  stocks  investigated.  in  of  Thirty-five  10 a n d  Tyria  in  presence  placed  Australian  differences  to  the  packed  as  responding  over  closely  such  the  evenly  had  early on  this.  whole  feeding  Only  the  released  feeding  individual  other  of  be  suggest  separate  but  group  were  to  in  aggregations  to  Similarly,  h.  was  variables, the  over  clump.  leaf,  at  out  3  were  there  leaves,  young  a  were  form  than  mine  distributed  distributed  do  aggregations  seem  rather  that  to  i n i t i a l l y  they  of  spread  tendency  were  randomly  of  -larvae  cm a r e n a no  sites  packed  larvae  leaves  favourable Two  tightly  After and  out I  of see  together.  genetic  were  severely  disease  or  constitution,  clumping  behaviour  affected  differences are  by in  responsible  remains  to  be  163  Thirdout  over  feeding they  and the  on  plant  the  gather  host  plant  upper in  or  between  prefer  sunny  other  and  display.  When  another  segments other  a  leaves  of  their  it  The  i s  motion hit  the  by  f l i c k  either  anterior  common  contact,  after  larva  Occasionally display  I the  in  the  could  lateral  induce of  the  w i l l  absence  hairs  these  w i l l  larvae  of  the a  head  stimuli  are  an  of  segments  are  in  solitary  antagonistic  lateral  f l i c k ,  both  or  physical  the  across  which  the such  the sides  hairs anterior  that  the  displaying of  the  sometimes  conjunction  body  used  in  with  the  may  not  segments.  The  averting  the  separately,  respond.  most  rapid  herbs  the  larvae  swinging  a  is  abdominal  by  on  Moulting  with  contacts  reacts  of  a  larva  to  or  their  however,  either  contrast  spacing  freguently  recipient  sometimes  plant.  by  posterior  by  host  grasses  larvae  l i n e .  display  the  spread  concentrate  periods  Fifth-instar  Usually  fashion,  moulting of  more  Frequently  react  often  similar  plant.  stems  be  s t i l l  rarely  individual.  The  the  fifth-instar  is  the  the  to  and  sideways.  The  on  tend  they  during  maintain  larva  larva  up  of  positions,  larvae.  feeders,  of  groups  the  larvae  although part  higher  project  or  fourth-instar  head-flicks  response head  from  respond  f i f t h - i n s t a r  i t s  the  obvious  f l i c k i n g  simply the  with  produce any  i s  may  or to  move  attack, own  out  of  although  head-flicking.  f u l l  head-flicking  stimulus.  display  by  larva  with  l i g h t l y a  fine  stroking paint  164  brush.  Sometimes  reaction. glued  The  to  lateral  a  response.  stick  The  f i f t h - i n s t a r younger  and  instar  larva  dropping  head-flicks produce  the  touched  react  a  silken a  by  to  some  their  larvae  stroked  times  before  classified or  as  than  can small  3.51,  1d.f., were  biotic  larvae  I  factors  tested  anterior  81  lateral  next  two  freguent  there  flicked  top,  paragraphs as  the  or  larvae was  p = 0.06). the  secondafter by  the  appear  to  that  a  in  hairs  with  the  more  strong  trend  that  number  of  are  brush)  off),  some  aggressive for  feeding  non-feeding  larvae  aggressiveness  show  the  were  a  were  reactions  moves  middle,  the  others  larva  than  influence  larvae  immediately,  aggressively  on  a  seen  leaf,  not  Large  =  increases.  do  discerned.  (Chi  more  Larvae  did  have  dislodged  away,  more  becomes  was  when  head-flicking.  reacted  and  I  a  moved  react  The  i t  on  the  rarely  occasion  is  to  plant.  one  towards  larvae,  larvae  larva.  the  they  although  foothold  when  Only  is  (head  whether  On  readily  (head  larvae 2  a  less  a  skin  e l i c i t i n g  If  aggressive  be  regain  in  instars.  produce  larval  responded.  defensive  trends  so.  f i f t h - i n s t a r  Some  e l i c i t e d  do  of  paintbrush.  effective  be  during  to  f i f t h - i n s t a r  younger  second-instar  stroking  5-7  to  thread,  secretions  of  a  necessary  head-flicking,  instars  elucidate  f i e l d  with  trying  were  equally  larvae  of  response  of  seemed  was  f l u i d  To  hairs were  second  on  strokes  display  larvae  f i r s t  several  or  was  the  same  bottom  of  the  aggressive larvae  behaviour per  plant  165  I the  examined  larval  response  equal-sized, 20  and  The  10  to  2  repeated S. I  moved  experiment other  8  off  larvae  plants.  The result  the plant  then  in  S.  In  with  4.46  one  2.5  On  I  5,  plant  at  h  plant  during this  put for  10,  over  towards  and  20  but  or two  other  linearly  no  the  and  four,  larvae/plant,  time.  plant,  h  was  period  this  2, 11  made  20  with  most  9  summary,  frequent larvae  2.19  displays  rate  rose  to  larvae,  and  3  By  the  none  end  had  h,  17  aggressive  compared  with  dispersers  from  larval  gradual  change  from  actively  maintained  by  an  host  I  and  of  the  left  the  the  group 2.74 the  gregarious aggressive  on  other i s habit  was  On  26  each  the  of  two  rate  dispersed  larvae  also  fifth-instar  dispersal  had  of  interactions  plant  put  larvae  development a  a  experiment.  plants  head-flicks 21  aggressive  off  small-scale  jacobaea  Within  the  of  another  flicks/larva/h compared  the  follows.  larvae/plant,  the  that  recorded  plants. with  5  left  dispersal  (field-growing) larvae,  had  plants  density  1  the  demonstrated  on  plant  conclusion  in  at  During  the  as  head-flicks  density:  head-flicks/larva/h  larvae  of  larval  head-flicks/larva/h  1.16  larvae/plant.  contacts  observed  of  between  jacobaea  number  larval  larvae/plant,  with 7.0  the  number  proportional at  to  larvae.  recorded  larvae.  relationship  flowering  f i f t h - i n s t a r  days  the  from  from  (4.30 other  the  headplant),  plant. characterized to  by  a  a  solitary  habit,  response  towards  other  166  larvae.  The  frequency  head-flicking some  as  plant,  response  yet  between  with  EFFECT  must  OF  is  a  undetermined  individuals) and  which  CROWDING  encounter  for  ON  f i f t h  function  larvae  search  the  LARVAL  of  to  exhibits  larval  rate  actively  another  instar  density.  (which  disperse  continue  may  from  their  the At vary  the  host  feeding.  DISPERSAL  Introduction The  aggressive  occasionally (previous larval I  caused  section).  densities  between  dispersal  of  Dispersal  when  larvae  occurred  rate  of  more  off  the  frequently  head-flicking  was  density-dependent  aspects  of  dispersal.  experimental  densities  of  was  larval the  abundant  and  encountering interactions unusually during per  a  within  were  high  are  larvae  fed  frequent, level  a  common  in  at  50 the  5  larvae a  of  f i e l d ,  my  high. the  I  chose  50  larvae  per  per  plant,  food  per  plant,  one  which  density l e v e l ,  of and  interest  of  larval  represented  experimental and  high  probability  treatment  crowding  the  low  larvae  but  at  investigate  and  intermediate  moderate  the  at  crowding,  The  supply  15,  with  and  of  outbreak.  food  reasons:  larvae;  represented  the  densities  the  other  Tyria  plant  following  5,  plant  also  to  larval  larvae  host  experiment  for  the  the  f i f t h - i n s t a r  following  plant  designed  responses  an  is.found 15  larvae  was  plants. was  well Such  largely  167  in  comparing  those  at  dispersal  the  other  rates  at  this  density  relative  with  two.  Method ( I  transplanted  plants area  into  and  plant.  a  Around  p l a s t i c  out.  For  plant)  late  checked the  each  the  pupating  the  top  of of  with  of  the  were  5  plants the  from  indoors,  fence  the  amount  each  at  that  to  of  or*  particular  25  (5,  a  jacobaea  River  s t r i p  1  larvae  from  15,  50  or  number  of  Dispersers determine  were i f  was  5  cm  climbing per  started larvae. left  I on  the  dispersing  in  containers  kept  they  of  each  larvae  larvae  collected  study  around  f i f t h - i n s t a r  and  larval  Chase  replicate  early the  S.  cm h i g h ,  prevent  feeding,  to  the  fastened  Each  noted  food,  I  treatments  enclosure.  without  mesh,  replicates.  daily,  in  mesh  Fluon  three  single-stem  pasture wire  fourth-instar,  plant,  larvae  flowering,  grazed  a  coated  there  with  closely  erected  wide  15  were  capable  of  the  plants  at  50  larvae  was  lost  the  weight.  Results After the  two  of  mean  there  and  of  on  of  of  the their  each  larvae  surplus  One  while  most  remaining  numbers  was  densities.  stripped,  leaves  larvae  days  lower  completely upper  6  food  the  other  on  plants  a l l with  replicates  had  inflorescences.  The  plant during  is  shown  the  in  Fig.  experiment  proportion 27  are  and given  the in  168  Table  19.  complete As at  50  to  A l l  the  development, expected,  larvae  the  per  was  density  level.  for  3  of  none  than  the  6  is  clear  at  there  to  dispersal  larvae  per  quality  was  rate  the  further  food  to  successfully.  dispersal  dispersal  days,  5  of  and  of  Although  required  pupated  quantity amount  the  larvae  probability  plant  the  15 l a r v a e  as  the  declining  interest  with  dispersing  was  plant,  of  the  at  the  surplus  food  was  very  dispersal  much due  in  part  food.  Of  more  intermediate on  close,  rate  higher  a l l  plants  particularly  at  the  highest  density. It dependent can  process,  change  dispersal larval  numbers  were so  Part  the  II  I  presence  eventually  be  experiments  suggest  larvae before  that  that  the as  dispersal  number a  of  larvae  conseguence.  often  higher  that  the  than  is  was  a  on  In  a  plant  addition,  necessary  non-dispersing  density-  to  the  reduce  larvae  could  development.  In i.e.  and  s i g n i f i c a n t l y  rates  complete  therefore,  (the the  discussed on  a  plant  supported that  density  point  of  the of  by the  that  concept more  the point  eggs  for  plant or  available of  stimulates  overloading  of  the  overloading,  larvae  biomass.  overcrowding dispersal) plant.  than  for occurs  can These many well  169  FIGURE  27  Rate of d i s p e r s a l from enclosed plants by f i f t h instar larvae starting at three density levels. Percentage p o i n t s a r e t h e means f o r f i v e replicates. Dispersing larvae were removed from the enclosures. C u r v e s f i t t e d by eye.  169  lueid e  uo  Dinmewey  <y  a  170 0  TABLE Number o f days on 50 l a r v a e  f i f t h - i n s t a r larvae plants with i n i t i a l per plant.  NUMBER 0  1  5. 0  5.0 (±0.00)  15. 0 50. 0  19  ON DAY  during s i x o f 5, 1 5 , or  :  3  4  5  6  4. 8 (±0. 4 0 )  4. 6 (±0. 49)  4.6 (±0.49)  3. 6 ( ± 1 . 00)  3.0 (±0.89)  13.8 (±0.40)  11. 8 (±1. 60  10. 4 (±3. 00)  8.6 (±2.72)  6. 4 (±2. 87)  5.6 (+2.24)  46.4 (+1.02)  39. 6 (±3. 83)  33. 4 (±3. 98)  25.2 (±4. 12)  18. 0 (±3. 35)  11.6 (±3.01)  Table  2  OF L A R V A E  remaining densities  gives  means  ±2 S . E .  from  five  replicates.  171  FREQUENCY  OF  DISPERSAL  IN  A NATURAL  POPULATION  affects  dispersal  rates,  Introduction Larval  density  experiment factors  was  not  on  larval  those  data  to  during  the  estimate population  or  on  of  in  i f  Tyria  dispersal and and  to  Thus  assess i t  accurately a  the  larval  the  to  see  disadvantages  of  of  other  possible  from  study  age,  In  of Yet  on I  such  addition  affects  a  natural  type  I  an  describe  plant  dispersal  dispersal  dispersal  jacobaea  larval  density.  not  how  previous  effects  population.  Senecio of  the  frequency  following  and  rates  i s  the  was  natural  one  dynamics.' In  stem),  advantages  instar  needed  association effects  dispersal.  estimate  f i f t h i s  designed  but  the  (rosette  estimated  relative  to  the  l o c at i o n  D  (Fig.  the food  supply.  Method The on  a  over  study  small 100  moving  Tyria  m.  into  done  was  location  marked  off  and  reference counts  in  Chase  population  There  was  Leaf  was  with number were  isolated  l i t t l e D.  The  stakes of  chance area,  in  each  taken  River  at  2  from of  m x 2  other  measured  m quadrats.  were  other  20  m by  The  r e c o rded  beginning  2),  populations  larvae from  which  plant the  at  and near  by  areas 10  m,  position  on the  a  map. end  of  172  the  study. On  Day  1 I  fifth-instar plant  i t  binary  larva  was  placing  covered  on.  dots  the  the  fourth  consecutive  ,days  day,  the The  were  found.  I  plant  that  study  was  of  427  marked  larvae  were  or  that  on  the  had  recorded entire  on  as  was  pens  replaced  depending just  once on,  when  remained,  by  individual  For  ten  during  and  each  marking  only  25  although  on  moulted  ' r e c r u i t s ' .  area  larva  larvae  ground,  obviously  terminated  marks  marker  been  every  feeding.  which  an  the  s t i l l  f e l t  noted  and  received  were  covered  with  each  each  Larvae  instar  number,  marked  bands;  plant,  from  recruits  yellow  marked  same  were  cohort  were  the  they  systematically,  individual  had  where  original  an  they  on  recruits.  area  When  carefully  noting  with  Larvae  on  number.  the  new  of  the  over  60  Results The  ink  survival  or  recruits  within  or  more  dispersal the and  Different  groups  of  kept  plants  similar  for  to  estimate  and  no  the  separate  35  and  the  Of  days,  were  present  with  or  laboratory.  unmarked  effect  checks  appeared  four  larvae,  in  marked  larvae  behaviour.  f i r s t  days,  on  the  of  were  42  25  done.  on  It  more  marked  the  as  eight  six  days.  markings,  were  than  dispersal was  their  for  more  dispersal  However,  affect  present  without The  to  larvae  were for  larvae.  handling  not  in  rates  were  d i f f i c u l t the  v a r i a b i l i t y  f i e l d in  173  the  response  times  and  uniform were  others  f a i r l y  the  rosettes  foliage  was  23%  eaten),  31% had had  been  Weather location 6  C,  as  to  day.  Of  29  plant,  and  between cm f o r  567  a  2  distances plants, the  few  113  larvae  second  dispersal  no rates  marked  and  handled.  jacobaea  plants  in  the  population:  plants.  Damage  to  the  plants  no  damage  of  their  l i t t l e  to  top  a  or  third  leaves  and  leaves  increase  flowers  l e f t ,  in  from  (<10%  of  foliage  (two-thirds  and  6%  of  the  stripped. uniform  high  was  23  larvae, were  during  C,  were 513  and  larvae  a  third  moved  to  a  160±12.7  move,  and  to  were  larvae  recruits  dispersed  to  54  large  travelled,  were  was  the  the  10  mean  days;  in  low  was  after  the  thermograph.  remaining  dispersed  there  more  were  were  these a  or  no  lower  marked  of  plant,  there,  few  daily  by  and  the  same  minimum  mean  Most  pupate,  study. the  the  a  showed  two  was  up  the  plants  addition,  day;  20% had  completely  recorded  Of f i r s t  lost  conditions  D the  plant, In  to  larvae  205? h a d  changing  there  stemmed  only  one  day  patchy;  had  on  Senecio  eaten) ,  eaten,  from  140  some  handling.  f i r s t  301  and  feeding  plants  to  the  were  with  remaining  constant  after  There  Tyria  larvae,  response  activity  161  of  were  second  plant, f i f t h  11  plant.  90±11.2  the cm  at  seen  probably the  end  always plant  dispersed  assumming cm f o r  that  marked  357 a  not  The  and to  of  the  found  on  remained a  means  for  the  move, third  fourth of  straight-line f i r s t  left  the travel  140+23.6 move.  174  The  dispersal  (original known  cohort)  age  Table  20.  Larvae  was  the  original  seen  larva  in  per  original  cohort  the  end  of  study  ended, days  more  less be  l i k e l y  l i k e l y  to  closer  larvae Table  near  agreement  were  observed  the  between for  than  between  5  days.  recruits. had  were  were  in It  5  to  Larvae  completed  pupate,  marked.  s t i l l  suggest  the  f i f t h  and  days.  were  the  other  present  data  the  they On  during  follows  from  development  i.e.,  only  original  more  difference  days  2  These  end.  of  when  the  their  f i r s t  that  larvae  instar,  that  there  and would  recruit  larvae  This  observed  in  number  of  is  when  20.  When a l l  the  moves/larva/day was  so  number  in  for  followed  early  presented  present  they  instar.  the  of  moves  for  records  are  larvae  of  when  disperse  to  for  number  records  were  rates  age  the  instar  f i f t h  do  were  unknown  was  to  they  to  recruits  left  short  the  of  instar),  had  with  the  and  important  higher  short  larvae  according  One the  much  1,  fourth  larvae  and  the  i.e.,  in  and  with  study  recruits  are  were  the  the  area.  the  Day  grouped  when  in  hand  few  the  day  rates  near  were  for  on  from  larvae  Dispersal  early  marked  (recruits  each  per  rates  0.14.  Hence  days  in  least  once  present  the  was  were  0.12;  pooled,  while  given  that  larvae  instar,  most  of  during  for  data  8 or  the more  instar. days  them In  the  for  the  recruits  usually are fact,  mean  mean  spend  l i k e l y for  number  only  the  from  8  to a l l  of  have  to moved  the  moves  value  per  11 at  larvae larva  175  TABLE  20  D i s p e r s a l rates of f i f t h - i n s t a r larvae of different a g e s . O n l y t h e r e c r u i t s were o f known a g e ; l a r v a e in the o r i g i n a l c o h o r t had s p e n t f r o m a few t o several d a y s i n t h e i n s t a r when t h e y w e r e f i r s t m a r k e d .  Days Present  No. of Larvae  No. of Moves  ORIGINAL 1 2 3 4 5 6 7 8 9 10  39 66 78 57 32 61 50 26 12 6  Moves/ Larva  1  Moves/ Larva/day  2  COHORT  0 6 17 16 19 22 21 17 9 6  0.00 0.09 0.21 0 . 28 0.59 0.36 0.42 0.65 0.75 1.00  0.00 0.09 0.11 0.09 0.15 0.07 0.07 0.09 0.09 0 . 11  0.00 0.37 0.34 0.55 0.50 0.50 0.53 1.00 0.57 0.00  0.00 0.18 0 . 17 0 . 18 0 . 13 0 . 10 0.09 0 . 14 0.07 0.00  RECRUITS 1 2 3 4 5 6 7 8 9 10  12 16 26 9 2 10 15 6 7 0  0 6 9 5 1 5 8 6 4 0  continued  on  next  page.  176  Table Days Present  20  cont. No. of Larvae  No.  of  Moves ALL  1 2  3  4 5 6 7 8 9 10  54 83 111 70 41 74 68 41 19 6  0 12 30 25 23 29 34 40 13 6  1  Moves/ Larva LARVAE  Moves/ Larva/day  2  3  0.00 0 . 14 0.27 0.35 0.56 0 . 39 0.50 0.97 0.68 1.00  0.00 0 . 14 0.14 0 . 12 0.14 0.08 0.08 0 . 14 0.09 0. 11  A 'move* r e f e r s to the completed a c t of dispersing from one h o s t p l a n t to a n o t h e r v i a ground dispersal only. (For movement t o a d j a c e n t p l a n t s see Appendix 3.) 1  As dispersal can be recorded only between s u c c e s s i v e days (i.e. Day 1 i s e s s e n t i a l l y Day 0) , daily rates are c a l c u l a t e d from Moves/Larva/(Days Present-1). 2  Includes 37 l a r v a e t h a t were found and Day 6, yet they did not appear as j u d g e d by body size. However, t rate was s i m i l a r to that for r e c r u i groups were s u b s e q u e n t l y pooled. 3  between Day 3 t o be recruits, heir dispersal t s , and the two  177  was  0.89.  tend  If  handling  to  be  recorded. of  a  low,  adjacent  3), thef  descending for  larvae  plant  and  to up  on  dispersed  from  held  for  and  for  those  (b).  The  more  mean  than  k by  the  rosettes.  low Of  rosettes,  avoiding  that  the  age,  than  from  were  f i r s t pnto  of  on  leaves  plants  were  as  dispersal  most  have  be part  those  of  common acts  over'  the  can  were  with  type  as  I  without  l i k e l y  crawled  of  plant  rates.  Many  stemmed  plants  found  on  rosettes  rosettes  s u f f i c i e n t  route  down  one  food  larvae  more  larvae  (Table  21).  rosettes  from  was to  that  other  (a), plants  7.1±0.71, meet  and  the  food  larvae.  preference  for  frequency  with  This  the  dispersed  had  155  although  population.  well  that  contact  seemed  may  estimates  dispersal  'changed  dispersal  that  number  the  of  these  plants  classed  This  some  of  rosettes  larvae  of  larval  but  on  such  simply  ground.  effect  90%  requirements  had  affected  This  not  acts  in  between  then  next.  the  also  were  leaves  were  travel, the  larvae  Moves  the  dispersal  successful  with  larvae  Besides were  many  but  to  affect  only  clump,  plants.  (Appendix  not  since  Moreover,  plant  assumed  did  stems  which  dispersing rosettes  preference  ground-dwelling  for  over  rosettes  dispersers  larvae  only  constituted stems  arthropod  i s  may  53% be  an  supported  were  found  on  25%  went  to  of  the  plant  adaptation  predators,  for  for such  178  TABLE  21  Number of fifth-instar larvae dispersing from rosettes and stems as (a) t h e i r f i r s t move; (b) t h e i r s e c o n d move. L a r v a e p r e s e n t f o r o n l y one day were omitted. Brackets give the proportion dispersing.  (a)  No.  Larvae First Found On:  On  Remaining First Plant  Rosettes  No. To  9  Dispersing Second Plant 23  (.28) Stems  (.72)  348  132 (.73)  (b)  No.  Larvae That Dispersed Onto:  On  Remaining Second Plant  Rosettes  (.27)  No. To  23  15  (.61) Stems  (.39)  90  27 (.77)  Significantly  more  (a)  c h i  2  =  27.91,  (b)  c h i  2  = 3.90,  larvae 1d.f.,  1d.fw,  Dispersing Third Plant  dispersed p<.001; p<.05  (.23)  from  rosettes:  179  predators than  to  are  larvae  on  included on  omitted  the  because  size  I  leaf.  Each  measured  density  larva  calculated g  8-leaf  for  a  leaf  plant  i s  1. e . , 0.16  rosette  on a  the  larvae plants  per I  on  an  larvae overload leaf.  chose  Larval dispersing  an  and  one  is  considered in  the  (Fig.  7),  as  8). For  is  a  This a  leaf  density Similarly  larval  compromise value  plants  was  non-dispersing  of  i s  of  larva  calculated larvae.  For  per  larvae  on The  leaf  rises of  on  is  a  6-  of  a  to  0.16  g  0.10  g  the  0.10/.335,  leaf  weight  exceeding small per  was  instar  exceeds  between  0.40  larvae  weight  weight  density  plant  plants.  a  the  a  on  overloaded  of  for  were  in  f i f t h  value  for  larvae  classes;  weight  leaf.  overload  two  density  but  of  non-overloaded  larval  a  of  were  performed  number  The  stem.  point  the  2).  (Fig.  per  as  of  v a r i a b i l i t y  consumption  g  when  on  the  plant  (Appendix  As  density  for  size  for  stems  effects  sample  density  a  the  on  similar,  Food  18-leaf  larvae  were  results small  which  stem  for  was  on  10-leaf  rosettes  different  analysis  larvae  0.10  significantly  similar  to  is  overloaded  0.30 g  larva  low-profile  of  assigned  or  over  analysis  correct  follows.  per  data  the  was  above  as  only  larval  plants,  level  were  Those  To  wander  rates  A  of  plants.  overloaded  leaf  rates.  to  stems.  following  rosettes.  overloaded  0. 335  jacobaea  rosettes,  in  on  l i k e l y  dispersal  dispersal  larvae  to  5.  climb  Because  more  and  of  0.48 large  leaf.  differently  for  non-dispersers  180  larval  density  plant  on  larvae, the  Day  before  one  day  the  conditions), closer  to  stemmed  day  these  on  overloaded  of  a  clear  be  for  larvae  larvae  more  than  and  When  only  there  is  a  than  to  had  plotted  such  to  as  and  This  unlikely  only  35  for  higher  the  This  end so  are  dispersal  of late  or  Larval and  can  marked  overloaded the  Table  lack  although  result  in  20)  on  larvae  quality,  I  1  found  for  22a).  had  levels  response.  were  disperse  recruits  non-overloaded  analysis  the  day  (Day  larvae  plants  (from  on  one  crowding  plant  remained  indicates  to  age,  affected  plants  larvae  plant  similar  such  both  of  unexpected,  multi-stem  nearing  the  (Table  larval any  to  is  was  the  dispersing  leaves  that  a l l  plants  For  on  non-dispersers  reacted  for  have  large  Although  on  1.  of  that  dispersing  obscured  s i g n i f i c a n t l y  above  density  density  appears  data  were  larvae  number  d i s p e r s a l / number  proportion  were  were  from  :  are  days.  the  as  data  dispersed,  larvae  activity,  calculated  dispersed.  two  of Day  dispersers  have  number on  they  On  1.  five  these  The  for. Day  these  plants  may  :  leaves  non-overloaded  example,  on  of  larval  variables  larvae  as  assumptions  response  corrected  of  the and  uncontrolled younger  My  whereas  plants  was  before  highest  the  When  number  density  dispersal.  tolerated  calculated  1/  larval  plant  age,  was  126  few  of  area  for  that  many  their  feeding  in  instar.  included  the  (Table  rate  from  the  f i r s t  22b),  overloaded  plants.  considered  only  recorded  181  TABLE  22  Number of fifth-instar larvae dispersing from overloaded, and non-overloaded, stemmed plants. L a r v a e p r e s e n t f o r o n l y one day were omitted. See text for other details. i  Larval Density  Number Staying  Number Dispersing  Proportion Dispersing  it  (a)  ALL  LARVAE  Less Than Overload  184  75  .29  Greater Than Overload  164  57  .26  (b)  RECRUITS  Less Than Overload  49  29  .37  Greater Than Overload  13  20  .61  Number of dispersers was overloaded d e n s i t i e s f o r the 1d.f., p<.05  significantly recruits: Chi  2  higher at = 5.10,  182  move  by  moved  a  larvae second  moved  onto  stems,  7  per  on  and  that  moved  larva  per  or  only  dispersal  higher  larval  If  plant?  If  (.45) as  a  another.  even Of  the  was  than  1.00  density  less  again. was  again.  the  Of  there  but  case  i t  when  onto larva  29  greater  Thus  density,  was  dispersers moved  where  than  many  larvae  that  dispersed  to  fewer  recruits  these  dispersed  Far  though  density  response  avoided plant,  the  inadeguate  answer  of  to  larvae  than  1.00  was  some  occurred larvae  at  moved  time.  host  adequate  where  densities  larvae  another  time,  stems  13  plant  plants.  one  onto  leaf,  f i r s t  third  plants  further  the  one  overloaded  were  leaf,  from  food is  did  benefit  food  supply  of  is  (on a  yes  dispersing  and  benefit  measured  (on -  eaten  they  supply  clearly  proportion  being  by  as  an  were  able  dispersing  the  non-overloaded 23a).  larvae  to  plant)  plant),  of  an  for  an  then  A s i g n i f i c a n t l y  had  adeguate  find  another  exchanging  overloaded  (Table  to  the  higher  food  after  dispersing. Although large host  number plant  some moved  (Table  non-overloaded their  chances  There between  larvae when  of  appeared l i g h t l y  there  23b).  plant,  improved  Of  but  was  these the  remainder  adequate  to  l i t t l e  and  heavily  s t i l l larvae  finding be  their  food  lot  by  adeguate 75%  moved  moved were  to  lower  discrimination defoliated  dispersing, food  on  onto  by  plants,  their  another  plants than  a  where before.  dispersers as  the  183  TABLE  23  (a) The p r o p o r t i o n o f d i s p e r s e r s t h a t i m p r o v e their chances of obtaining food; (b) the numbers of dispersers t h a t d i m i n i s h , i m p r o v e , o r do n o t alter, t h e i r chances o f o b t a i n i n g f o o d . Data f o r f i r s t and s e c o n d moves o f f stemmed p l a n t s a r e p o o l e d . Overload point is 0.40 l a r v a e / l e a f . Brackets contain sample sizes.  (a)  Type Host  of Plant  Not Overloaded Overloaded  PROPORTION Before  OF  DISPERSING  Dispersal  After  .60  (125)  .40  NUMBER Plant 1 Conditions Not  OF  . 20 (32)  L A R V A E ON  PLANT  2  Plant 2 Is Not Overloaded  Plant 2 Is Overloaded  74  21  51  11  Overloaded Overloaded  Dispersal  .80  (95) (62)  (b)  LARVAE  Significantly more larvae plants after dispersal. Chi  2  are on = 25.48,  non-overloaded 1d.f., p<.001  184  proportion abundance  EFFECT  found of  OF  on  those  PLANT  heavily  defoliated  plants  in  the  DENSITY  ON  DISPERSAL  plants  reflected  the  population.  SUCCESS  Introduction  host  Because  there  plants  (previous  experiments plants were  at  run  to  dispersal  cases  of  food  successfully density.  than  the  in  the  shortage.  Those  success  by  larvae  undertook  plant  place  dispersal  dispersal I  how  younger  takes  severe that  section)  l e v e l s ' of  larvae  most  considerable  determine  different with  however,  is  the  f i f t h f i f t h  few  following  larvae Only  a  find few  instar,  host  t r i a l s  instar  because except  t r i a l s  do  with  larval  increases  between  in  indicate, age.  Method A l l River  study  that  was  run  in  there a l l dish  with  1  area  f i f t h - i n s t a r on  occasionally a  was  similar more  t r i a l s . in  Senecio kept  t r i a l s  for  some  grazed  closely  centre  jacobaea  f l a t ,  habitat  A number  the  a  of  by  of  cattle.  Williams  larvae a Prior  without  were  well-grassed  cropped.  plants. time  at  larvae  The  area  release  food,  viz:  the  was  in of the  Lakeside  the  the  an  open  larvae min  were grass  same  naturally  30-40  Chase  t r i a l s  although  procedure  mapped  in near  other  Farm,  placed  to  area  The  were  run  petri growing  had for  for  been fifth-  185  instar,  20  disperse,  and  The larvae  a l l  other  were  to  4  were find  the  h.  other  2/m  Thirty  f i f t h  instars.  checked  exceeded  within  with  for  t r i a l s  time  density so  min  every  The 1-2  larvae  run  for  plants.  For  most  over  a  day  t r i a l s  larvae  that  found  a  40  larvae  were  used  for  instar,  and  50  to  larvae  per  to  give  the  where  the  or  left  h.  often  2  were  plant  t r i a l  plant  had  each were  done t r i a l  used  for  instars.  Results The plotted third  and  total  of  the at  results (closed  100  larvae. locating the  instar  The a  There there  to  the  The  plant  orienting  of  sun,  data  11  is  the  was  no  clear  Two  per  of  2  for  two  The  were the  0.38,  Each  a  at run  larvae  plotted t r i a l s ,  eguation  t r i a l s  m ,  was  Williams with  value  for  giving  a  fitted  to  Farm,  each  second-instar  proportion  predictable  are  successfully decrease  from  larvae. of  trend  the  distribution a c t i v i t y .  mean  evidence  although  28.  point.  only.  value  f i f t h - i n s t a r  Figure  each  plants  plant  with  in  third-instar  was any  for  mean  host  success  was  of  t r i a l s  instar  larvae  density  8  circles)  fourth  f i f t h a  of  in  some might  trail-following direction  t r i a l s also  were have  of  run  by  larvae,  travel on  relative  overcast  obscured  nor  any  days. sun-  186  FIGURE  28  Effect o f p l a n t d e n s i t y on t h e a b i l i t y o f l a r v a e to l o c a t e a new h o s t p l a n t i n a g r a z e d p a s t u r e . For the t r i a l s at 0.2 p l a n t s / m 40 larvae were tested in each t r i a l . Other t r i a l s with f i f t h - i n s t a r larvae w e r e r u n w i t h 30 larvae per t r i a l . The equation d e s c r i b e s o n l y f i f t h - i n s t a r d a t a . The p l o t t e d values for t h i r d and f o u r t h i n s t a r l a r v a e a r e t h e means of t w o t r i a l s , e a c h w i t h 50 l a r v a e . Each datum point g i v e s t h e p r o p o r t i o n t h a t was s u c c e s s f u l i n locating a p l a n t when r e l e a s e d a t a c e n t r a l point. 2  186 a  • III Instar A IV Instar © V Instar c _co CL  co cz CO  o o  _J  CD CO > CO O  CO O  Plants  Per  Metre  187  \  Fourth-instar dispersing fourth  as  instar  what  and  plants  plant  very  vegetation, (Dempster instar  of  grass  the  a b i l i t y  more is  of  to  should  be  levels  changes  in  be at  expected;  success  curve  at the  successful  which  the  given  I  losses  ran  where  larvae  does  although  dispersal  Fifty  i s  with  successful  densities  increases  which  areas  lower  as  rises  off  would  predation  terrain.  much,  larvae  at  be  larva  rapidity  level  of  1971).  much  density  the  between  local  at  to  although  f i f t h - i n s t a r  The  length  movement  rates  a  as  vary  The  high.  find  That  density.  pressure  some the  were  dispersal  not  seem  as  a  to  to  affect  the  consequence  of  predators  additional  grass  tested  to  the  that  I  was  each  edge  of  did  not  higher  with  of  4  f i f t h -  or  height,  c i r c l e  of  denser  be  10-15 cm,  grass a  well  t r i a l s  <5 c m ,  at  may  rate  >15  and/ m  cm the  diameter  similar. Several  dispersal and  larvae,  surprising is  probably  were  f i f t h - i n s t a r  plants  is  with  appear  to  investigated. finding  larvae  factors  success.  increase  may  cause  know  i f  the  risk  as  the  size  of  predation,  predation and  or  disperse  Probably  such  temperatures  dehydration  larvae  extreme.  Low  food  of  heat when  more  intensity, reserves  measure  may  whereas  the  nature the  larval  high  exhaustion.  of  are the  temperatures I  do  conditions  the  biotic  ground  individual  affect  movements  However,  weather  importance  of  slow  could  are  factors  cover,  larva.  not  The  and areas  188  used  in  these  invertebrate  LARVAL  experiments  fauna  -  BEHAVIOUR  appeared  although  DURING  I  took  to no  support  a  systematic  diverse  samples.  DISPERSAL  Introduction The new  previous  host  located  plants plants.  distance  at  investigate to  ignored The  which the  elucidate  host  experiments  the  the  pattern  how  movement.  sense  I  larvae  to  larvae  distinguish a  larval  specific  of  of  experiments  larvae  of  a b i l i t y  problem  following  Tyria  how  on  find  actually  determine  the  host  and  did  plant,  not  organs  were  used  food  for  attempt to  locate  plants.  Method Fifth-instar h  then  released,  grassed  area.  After  freshly  cut  to  and  larvae  the  lowest  S.  side, leaves  were  could  be  measured  plant  on  the  sometimes  To  f i r s t  several  check  kept  without  one  at  time,  they  jacobaea as  were  had plant  well  as  removed more  started at  so  presentation  that  the  per  on to  of  If  the  the  the  line  of  I  2.0  held (2-10  travel.  a cm) The  distance  continued  was  -  cropped,  larva-stem  larva  plant  closely  distances  their  that  a  crawl,  different  ahead,  easily.  times  a  0.5  past  presented  the  again;  larva.  larva  was  indeed  searching  for  a  host  189  \  plant,  and  not  presentation cms,  but  climbed  the  plant  for  discarded  of  -  data  a  the  groups  and  nail. of  two  larva was  of  crossed  tested  data  for  made  for  made  out i t s  several  jacobaea  of  stem,  of  several  larva. i t  touched,  then  the 5  If  had  i t been  avoided,  I  distance  cm,  crawling  but  driven  in  seemed  therefore  which  used  the a  for  estimating  past  accurately at  a  cm  larvae did  2  were  high),  after of  at  m diameter  larvae  to the  'reactive  larva  orients  and  were being  the  egual  c i r c l e  trimmed one  released  location  of  at food  the  within  the  the  c i r c l e  without  locating  were not  a  stem,  discarded feed.  as  they  flowering  was  placed  the  centre,  for  1-2 and  c i r c l e .  described  when  closely  sun,  larvae  to  a  from  plant  without  distances  on  by  response  or  more  leaves  three,  movement  were  distance  were  (50-70  were  f i n a l  of  assumed  than  method;  measure  lower  or  distance  that  less  larvae  Fifth-instar  records  pattern  S.  plants  was  the  plant.  nails  The  a  made  individual.  was  maximum  I  crawling  I  suggested  the  host  at  the  plant  that  circumference  jacobaea  in  the  plant  to  of  feeding  unreliable  a  lawn.  each  for  while  Twenty-five  on  If  s i t e ,  plant  front  began  host  the  towards  cropped  in  experiment  distance'  around  pupation  jacobaea  and  somewhat  following  i t s e l f  S.  plant.  distances a  a  experiments  recognition  be  a  the  These  these  the  directly  searching I  of  for  a  h, the  If  a  plant  i t  above.  rejected  The the  190  Some the  side  two  t r i a l s of  the  c i r c l e  groups,  plant  the  same  and  run  one  50  of  group  cm f r o m  diameter  with  closest  each  simultaneously: the  were  but  to  the  three along  the  150  plants  a  only  sun. larvae,  plants,  and  the  the  For  diameter  cm f r o m  on  6  nails  these  t r i a l s  were  at  the  released  right other  on  angles group  to  along  plants.  Results  In  the  Senecio cm.  On  f i r s t  jacobaea only  one  plant  the  plant.  stem  and  continued  and  several make  larvae  the  the  with  50  larvae  presentations at  distance  between  larva  successfully  the  2-5  of  and  I  plant  a  stem,  10  the made  of  plant.  a  and  cm o f  direction.  located  of  of  direction  within  changing  cm  a  change  passed  without  2-3  21  larvae  larva  larvae  within  experiments  by  there  larvae  directions  both  groups  direction the  a  distance  passed  c i r c l e  travelled  In  3  a  made  5  Again,  but  failed  on  one  to  contact. In  of  only  did  walking  at  I  different  Frequently  presentations  cm,  to  occasion  climb  28  experiments  general cm.  of  shape  was  travelled the  plants. of  large  6  plants  l i t t l e  released  64% of the  with  50 by  positioned  difference  cm  from  larvae  larvae  objects,  the  at  directions compared  150  distant.  cm  right-angles  larvae at  the  plants  released  moved  Therefore  in  least  side  do at  not a  make  to use  distance  the of of  191  With climbed  plants  plants,  on  while  With  the  reactive  f i r s t  experiments),  at  finding  the  plant  the  a  plant)  around  are  that were  c i r c l e ,  the  cm  this  larvae  ratio  32/4.4,  can  be  to  This  was  which  the  for  for  given  a l l  the  find  a  plant  i s ;  number  gives  an  z  total  expected the  a  1 d.f.,  of  side  of  'reactive  :  reactive  the  of  the  of  distance  expected  the of  number  tested/4.4,  of  value  (of  p<0.05),  zone'  and  total  number  observed  width  circumference  the  For  The  plants  circumference  the  successful  each  estimated  repeated  (from  7.3. 12)  and  a  of or  This  in  2  is  chi-  therefore  too  estimate.  If  we  reactive  repeat  these  distance,  which  not  give  but  suggests  an  the  the  agrees  that  point i t s  direction  calculations expected  closely  accurate  approximate  general  cm  therefore  = 3.92,  to  (2  cm  1 and  (chi  If  follows.  :  sguared  12.3,  give  as  and  c i r c l e .  cm  larvae  4.4  than  an  4  of  the  2.0  calculated.  lower  low  and  be  was  significantly test  calculated  Then,  to  number  contacted  outside  c i r c l e  was  w i l l  wandered  larvae  of  zones'  that  expected  added  12  estimated  the  summed. ratio  nails,  larvae  measured,  plant.  values  'reactive  was  20  25  distance  plant  base  a l l  number  with  the  determination value  probably  at  which  a  of  of  larva  travel  travel  for  of  4.0  the lies  cm  successful  observed  of  the  line  using  This  reactive  crossed  the  from  the  most  larvae  3  is  does  distance, and  c i r c l e  centre, is  the  larvae  value.  between  as  away  5  cm.  is  used  then  the  from  the  192  sun  (Fig.  29) .  I  periodicity  of  in  I  the  f i e l d  When  saw  straight  changes  > 45°. an  while  made  c i r c l e ,  and  Rates In  these  over  2  distance  17  More  > or  experiments diameter  made  of  movement  3  min.  in  1 In  which  c i r c l e  in that  within  5  27  had  Given without host  that  food  plants  cover  a  (van i s  lot  habitat,  which  towards  S.  leaves  m,  (>45°)  other  60  the  8 reached min,  a  larvae 1971),  can  direction  (20  larvae),  leaving  the  individuals. and  cm  took  the  same  described centre high.  the  some  of Of  a the  4 m 75  circumference  and  46  survive  their  consequence  of  and  hence  to  compensates  for  their  short  host  cm  a  direction  travelled I  15  ground,  each  20  in  had  reached  min.  Meijden  l i k e l y  no  frequently,  to  15  day.  travelled  between  from  <5  the  direction.  section  within  although  changed  larvae  dispersed  so  exists,  before  in  rested  experiment,  diurnal  making  f i r s t  tremendously  fifth-instar der  the  from  the  tested  larvae  previous  done  57  changes  while  i t  c i r c l e ,  the  larvae  the  jacobaea.  around  vary  within  most of  more  grass  in  circumference  or  larvae  tested min,  the  turns  some  travel 5  of  i f  of  throughout  the  within  two  larvae  the  45°  12  to in  out  of  estimate or  dispersing  frequently,  angle one  activity,  larvae  line  experiments h  quantitative  larvae  released,  through  no  dispersal  f a i r l y  28  have  Also, plant  there that  several  a b i l i t y their  search  a  to  find  new  a b i l i t y  to  large  reactive  are  usually  reach  the  days  area  of  distance  several ground.  lower These  193  FIGURE  29  Line of point of circles stems.  travel of 57 f i f t h - i n s t a r larvae at the crossing a circle of 1m radius. Solid indicate positions of Senecio jacobaea  193 a  D i r e c t i o n of S u n  V  194  greatly  increase  the  effective  reactive  f i e l d around  each  stem.  REGULATION  I  have  larvae  AND  LARVAL  shown  that  dispersed  dispersal  occurs  instar;  these  they  are  to  when  the  food  s t i l l  by  within  5  cm  particularly  I  are  that  may  First  and  that  another.  in  on  the  f i f t h  to  the and  f i f t h  Larval  (and  last)  find  another  plant  A l l  instars  disperse  on.  i n i t i a l  instar In  the  many  host  plant  has  been  often  disperses  when  latter  situation  dispersal  the  proportion  that  i f  there  i s ' is  disperses  can  i t ,  often  locate  but  by  a  covering  successful  when  host  at  the  density  facts  can  plant a  lot  only of  S.  they  ground  finding  of  when  f i f t h -  another  jacobaea  host  exceeds  4-  2  hypothesis  fifth-instar  plant  to  Tyria  m .  suggest  occur.  of  later  of  plant,  per  population  successfully  larvae  larvae  plants  frequently  plant.  instar  5  host  HYPOTHESIS  density.  Dispersing are  natural  one  crowding,  with  A  need  the  the  a  -  usually  supply  on  stimulated increases  most larvae  but  food  in  from,  pupate  exhausted,  DISPERSAL  these enables I  us  assume  larvae  are  density-dependent  to that  be  predict  brought when  aggressive  common  to  dispersal  a l l  together  outbreaks  of  interactions populations  occurs  as  a  of  in  a  Tyria between Tyria,  consequence  195  of  these  suffered and  interactions. during  thus  of  larval  regulates  hypothesis,  dispersal  checks  populations  of  is  the  Tyria,  that  rate  mortality  of  before  increase,  they  run  out  food.  Most  dispersal  £§£  occurs  proposed  mechanism  this to  The  appears  operate,  disperse the  better  than  to  i t  i t s  regulating earlier  in  and  (if  the  consequence  instar,  primarily  which at  effective  also  the  most  advantageous  to  disperse  is  of  conseguence  follows  the  intervening  period  at i f  i s ,  the  to  the  greater  from  the  Indeed, mechanism  a  larva  the  (Fig.  the  to  larva, 28).  Any  a c t i v i t i e s  many  f i f t h  of  individuals  instar  other  extent,  the  for  older  too  that  the  plant  c r i t i c a l  some  time  through  remove  crowding  stage. for  The  another  mortality to  time  a l l ) .  operated  l i k e l y  operates  i n t e r v a l ,  finding  which  more  at  of  suggests  this  most  mechanism  this  a  the  This  longer  f i f t h  as  be  chances  which  occurs  operates  has  instars  one  that  period.  factors  in  unpredictable.  The  chance  of  'unpredictable  mortality•.  The  density  whether  or  numbers.  For  that  plant  in  the  any  survives  Therefore which  not  density  the  host  proposed  given  plant  is  density  increases is  plant, mechanism  dispersal  dispersal  when turn  of  very  the low  rate  S.  jacobaea,  w i l l the  determines  effectively  proportion  a  function  of  i s  high  dispersers  growth the  rate  most rate. of  reduce  of  plant  larvae  density. survive,  Conversely,  increase  will  be  when most  196  severely If  curtailed. the  important  check  populations this  expand  i s  plant  larvae. is  per  when  m .  I  2  sufficient factors, when  Tyria  the  do  density  Table  24  refer  ha  to  40  in  4  Chase  plants  an  assume for  the  an  of  high  plant  Tyria.  say  high  outbreak  mortality,  than  may  high  a  have  one  plant  is  also  develop.  keep  is  that  density  to  a  of  prediction  outbreaks  plant  can only  density  The  less  We  survival  populations  finding  low,  that  separate plant  numbers  less  where  were  accuracy.  I  the  in  jacobaea the  locations  densities  of  population  Only  by  high  greater.  of  of  possible  or  2  allow  a  Other low  even  high.  11  S.  m  that  was  ensure  an  absence  density.  are  River  outbreak  defoliation  to  to  indeed should  The  plant  Tyria  per  . predicts  is  of  is  absence  density.  high  enough  reasonable  ac).  areas  the  pupal  and  the  24  high  density  l i s t s  with  with  dispersal i t s  higher  f a l s i f i e d  as  plant  Table  were  i s  not  such  constitute  some  outbreaks  for  plant  complete  (5  to  condition  estimated  then  about  be  occurred  numbers,  For  condition  therefore  occurred  during  that  hypothesis  necessary  suffered  associated  density  density  The  can  on  predict  dispersing plant  to  check  therefore when  mortality  an  S.  outbreaks  known,  define  an  jacobaea  or  could  be  outbreak  as  plants  area.  Most  of  populations  that  covered  Myrtle than  2  Point  and  ha.  These  Amboy two  of  the  that  areas 2  to  in 16  populations  areas  also  had  197  TABLE A l i s t o f S. j a c o b a e a coincident with Tyria stems per m are given.  24  densities in outbreaks.  different areas Only flowering  2  Year Of Outbreak  Plants /m  Henley-On-Thames England  1931  24  Weeting England  Heath  1967  4  C o a s t a l dunes Netherlands  1970  5±1  van  Fort Bragg California  1964  21  Hawkes  Jordan Oregon  1968  >5*  D.Isaacson,  Location  Myrtle Oregon  Point  1970 1970  Crescent City California  1970  >10  Top F i e l d Chase R i v e r , B .C.  1969  3  Power Chase  1971  6  1968  14  Durham Nova Scotia  Source  Cameron  1935  Dempster der  1971 Meijden  pers.comm. pers.comm.  C.H.Shanks,  >5i  1970 ( F i g . 3  1973  L.Cannon,  2 - 5 1  Amboy Washington  Pylon R i v e r , B .C.  Data  2  pers.comm.  1  L.J.Garrett,  2  W.Q.Green  pers.comm.  W.Q.Green P.Harris,  •-Approximate e s t i m a t e only. Estimate was made i n 1 9 7 1 ; s t e m i n 1969, probably around 5/m . 2  2  pers.comm.  density  was  higher  198  dense §•  stands  of  jacobaea;  fauna  and  low  populations In  a  and  situation  that  survival  were  no  grasses  was  prediction.  Further  two  where  areas  density. population  at  than  0.1  per  pupal  mortality.  that  was  The  density  the  larva  starve  to  i s  of  factors  enough  is  a  of  a  negate  the  description  of  population  California,  plants  was  1.9  about  Tyria  mortality  had  to  at  was  less  to  high  of  Tyria  in  per  low Tyria  density  River,  of  jacobaea.  density  Tyria a  to  Tjjria  density  plant  low  the  persisted  low  where  arthropod  S.  Mile  to  attribute  rarely be  and  was  the  1967.  m ,  and  2  in  occurred.  Hawkes  European  earwig,  the  have  mortality  proximate  eaten  (starvation,  dispersing  low  describes  buildup  death,  experimenter,  different act  i t  stands  jacobaea  the  high  the  L.  d i f f i c u l t  because  the  Ten  the  auricularia  dispersal  by  England  flowering  of  S.  studied  (1973)  at  dense  and  a  among  Nonetheless  evidence  attributed  Hawkes  much  i s  may  He  2  1967-1973 no  attributed  It  m .  Wood,  established  period  Forficula  (1971)  suggest  density  Tyria  growing  1971).  the  plant  both  Honks  of  in  supporting  Dempster  would  (Dempster  expanding  case  herbs  by  i t s  a  predation,  ultimately  cause  spider,  death  directly of  or  accident). for  death.  stepped  attributed  responsible  to  to  on  three  Yet  the  A  the  larva's  demise.  I  designed  dispersal  and  executed  mortality,  a  f i e l d  combined  experiment  with  the  to  see  observed  if egg  199  distribution, that  I  Nosema  could  predicted. spp)  and  experimental on  plots.  As  I  description  of  predictions  in  hope  this  a  the  that  the  viral  results  the  9  were  days not  omitted  a  4.  I  experiment  at  in  k i l l e d their  populations  being  and  may  some  wish  future  this to  the  established  have  included  of  test  of  the  included  assumptions,  have  (possibly  60-95%  reasonable  them,  investigators  role  microsporidian  of  experimental  Appendix  other  a  infection  within  have  particular  s t a b i l i z i n g  Unfortunately  larvae  predictions  the  play  a  design,  and  Appendix  with  refine  and  rerun  time.  DISCUSSION In out  of  Part the  II  local  describe  the  within  local  a  (1927)  'dispersal' area.  movement area.  in  search  of  of  ' t r i v i a l  movements'  local  area.  and  different  use  of  attempts  to  distinguish  term  ' t r i v i a l  sense; example,  the are  movement' distances vastly  to  (1969,  terms  one  are  reserve  Johnson  the  from  in as  has  been  than  of  Chapters and  by those  another  with  Elton's  has  in  a  migrating travelled  of  mates",  movements traced  dispersal,  of  to  to  movements  processes.  thought  used  their  for  1,2)  adults  movements  local  dispersal  separate  travelled  greater  "...the or  of  was  host-plant  classify  migration two  movement  agreement  shelter,  tend  to  the  dispersal  dispersal  now  to  III  usages  food,  entomologists  a  larvae  of  although  of  Part  Both  description  animals  In  referred  and  Possibly  as out the the the  comparative locusts, by  for  nymphs  200  within  an  area.  prejudging  the  individual.  For  this  by  dispersal,  of  spread.  act  of  dissipation  such  as  a  larvae  Yet  for  processes  differ  both  appear  them  quickly,  but  in  without large  large  force  in  the  f i e l d  do  k i l l e d  although  success  in  in  density  (Fig.  Because  and  greater  larvae  a l l  was (1963) the  of  to  dispersal  crowded  as  as  on  the  " . . . t h e  from  the  movement  was as  spread  plants.  to  distinguish  emphasis  or  the  dropped.  referred  describes  adult  and  so.  to  der  lesser  to  a  focus  movement  of  I  use  the  term  I  believe  the  Not  Yet  only  can  they  larvae  1971),  search  predation  is  an  chance  instars  and  many  clearly  becomes  move can  for  f a i r l y  go  several  predation S,  important  jacobaea mortality  dispersing  predators. of  i t  Hence,  to  1971),  fourth-instar  i f  a b i l i t y  arthropod  the  extent  disperse;  Meijden  the  by  a  f i f t h - i n s t a r  (Dempster  the  f e l t ,  be  for  is  scale.  have  instar,  plant  less  adapted  area.  undoubtedly  to  in  (van  larvae  a  they  addition  food  over  are  to  Donnelly  accurately  well  for  area  one  movement  should  concentration,  larvae,  necessary  aside,  a  term  definition  larval  only  Fifth-instar  days  of  overloaded  dispersal  larvae,  where,  movement'  larval  local and  their  ' t r i v i a l  local the  a  birthplace",  from  of  MacLeod  idea  using  reason  within  •interspersal' from  by  importance  Movement  it  Yet  The  successful increases  larvae  older  the  dispersal, with  a  rise  we  might  28).  often  f a i l  to  reach  another  plant  201  ask:  Under  what  individual?  conditions  Clearly  defoliated  plant.  are  pupate  able  maximum  to  potential  (Dempster of  When  If  later,  In  advantages  d i f f i c u l t  to  one  of  overloaded implies the  assess.  two  the  to  be  predators Stayers the  and  l e f t  up  The  second  plant.  a l l  the  or  feed  risk,  on  population  I  (Fig.  i t .  be  non-defoliated  30). the  are  more  placed  but  a  only  plants.  if  there  risk  a  over  Being  a l l  is  no  non-overloaded,  the  have  in  Overloading  Clearly  find  studied  chance  non-overloaded.  face  also  their  plants  dispersing  from  to  and  pupae  defoliated.  dispersing  unable  lower  defoliated,  but  fecundity  a  can  a  of  suitable  excess  food.  50%  the  of  This  ground plant. Yet  in  larvae  point  w i l l  be  the  relative  later.  of  If  become  not  plants  being  to  than  lowered  have  the  plants  less  a  large  or  Dispersers  being  neither  f i e l d  advantage  and  of  non-overloaded,  taken  by  plant.  face  natural  may  in  to  leaving  non-defoliated  overloaded  continue  gained  non-defoliated  from  at  pupae  do  Non-defoliated  plant  present  than  in  defoliated  so  results small  from  on  do  dispersing  different  that  advantage  of  classes;  is  larvae  addition,  advantageous  advantage  w i l l  which  disperse  relative  an remain  they  successfully  larvae  dispersal  is  larvae  weight,  1971).  overwintering  there  is  situation  dispersing the  larvae  from  larvae would  to a  i s  non-defoliated,  stayed,  starve;  consider  the  hence  plant some  but  would  be  dispersal  overloaded defoliated would  have  202  FIGURE  30  O v e r w i n t e r i n g s u r v i v a l of pupae class. F i f t y - f i v e pupae i n each groups of two or three under d e b r i s . Pupae were p l a c e d o n l y w e r e b e i n g u s e d by o t h e r l a r v a e  according to weight c l a s s were p l a c e d in stones or vegetable under objects that for pupation s i t e s .  202 a  P u p a l Weight © >140 mg o 1 1 0 - 1 2 0 mg A < 90mg  203  been  advantageous.  dispersers dispersed moved were  left 13%  from  were  'worse  better  off,  i.e.  food  by  supply  in  fact,  within  5cm,  simply  to  The  work  this the  on  cannot  only  to  abundance  assess  of  larva  larvae  stemmed  larvae  that  i.e.  to  not  in  appear  was  the  due  area.  that  area  i t s  distances  supply  plants  the  non-  plants,  at  suggests  in  33%  increased did  food  they  However,  plants  host  also  conditions  the  non-defoliated  individual  discrimination  food  and  suitable  of  overloaded  dispersing  in  the  plants.  average  towards  improvement  larval  the  40%  dispersing,  from  defoliated  oriented  a l l  overloaded  moved  As  Of  after  Therefore  between  population,  plants.  they  dispersing.  discriminate  f i e l d  o f f  non-overloaded  plants.  and  the  overloaded  overloaded  to  In  larvae  before  they  disperse.  Assessing defoliated  but  because  the  reducing  the  conditions concluding have  to  the  selective  overloaded  departure  become  better  plus  question  pertinent  to  some  on  that  many  of  dispersal  of  mean  their the of  this  the  is  food. for an  associated on  a  selection  analysis.  of  i s  larvae  pupal  larvae kin  advantages plants  pressure  determine  dispersers Because  the  dispersal  made  more  those  weights  of  survival  for  w i l l  the  d i f f i c u l t stayers  stay.  Before  one  dispersers rates from  dispersive  by  leave,  t r a i t  be  non-  larvae  that  a l t r u i s t i c  plant  more  benefits As  from  would  and  non-  as  larvae.  one  female,  traits  i s  also  204  The  tendency  defoliated factors into in  plants  other  the  plant  clear, which  to  be  quality  large  rate  per  densities.  process,  i n i t i a t e d  There  whether  are  no  aggressive  larvae  exchanges  dispersers p r i o r i  rate  of  Also,  behaviour;  some  defoliated  plants  their there  One as  was  others  was  the  rate  before  plants  the  f i e l d than  I  found  per  plant  excess  a  density-related  food  dispersing  responded,  for  assuming  at  whether to  old,  failure  dispersed  I  the are  the  most for higher  fifth-instar in  variability on  have  exchanges.  that  there  larvae  nor  such  as  wonders  remained  It  had  lost  marked  changes  seemed  in  or  opposed  a  look  influences.  merely  or  by  this  larvae  is  put*,  success  larvae while  or won  »stay  young,  15  whether  grounds  vertebrates.  reflected  exchanges.  established  by  experiment  larvae  possible  not  overloaded,  field  at  the  and  dispersal  dispersal  other  individuals  t e r r i t o r i a l dispersal  a  although  did  affected  from  a  higher  larval  not  aggressive  determined  much  in  I  larvae  non-  triggered  defoliated.  other;  frequently and  is  crowding  each  leave  stimulated  more  of  to  to  food.  is  triggered  plants,  of  for  fifth-instar  more  Hence  have  become  that  plant,  need  level  larvae  dispersal  dispersal  reacted  was  regardless  I  the  Young  dispersed  5  that  cue  non-overloaded  at  that  plants  larvae  dispersal  fifth-instar  immediate  that  defoliated.  than both  as  proximate  population  that  an  p o s s i b i l i t y  the  from  many  implies  than  however,  at  were  of  aggressive in  larval  overloaded,  nearly  two  or  even  three  205  times.  As  Wellington  individual  behaviour  instructive  to  females,  from  various  and  but  conducted,  to  dispersal  in  consider dispersers major  rate  the  of  heavily  the  of  natural  0.12  appeared  to  be  clumping  was  positive  effect  It other  would  be  on  densities, a  positive  by  to  i f  some  and  and  i t  studied, per S.  larval  for  need  but  to that  also  the  the  mean  dispersal  reflected  jacobaea  plants  Mortality larvae  both  and,  during  dispersing.  wasteful  dispersal,  effect  which  to  a  dispersal  increased,  by  the  rather In  this  of  l i k e l y  egghad  a  growth.  repeat  since  are  select w i l l  a  success.  day  supply  appears  benefits  stay,  dispersal  more  larval  These  experiments  the  that  potentially  Tyria  on  point:  further  larvae  I  be  different  female.  conclusions  of  effect  same  Any  population  useful  task,  on  would  from  stage.  food  the  reduced  populations  plant have  their  therefore,  this  crowding.  low,  the  in  investigation.  to  larva  of  larval  decreased,  await  larvae  conditions  population  f a i r l y  of  i t  of  density  condition  extent,  of  selection  per  variability  set  those  moves  grazed  population  on  plant  greater  than  kin  that  population,  clusters  what  larval  only  the  discussion  determine  shown  activity  impossible  confer  effect In  not  not  the  questions  the  has  affect  different  summarize  d i f f i c u l t  can  compare  behavioural  To  (1960)  this  which  have  dispersal  population  study  of  dispersal  different  larval  on and  w i l l  not  necessarily  growth.  When  fifth-instar  206  larvae  were  finding  host  m  2  80%  to  33%, in  effect  affect  is  plant  i s  determined increase density  plant  from  would  be  necessarily  in  11  widely  density  of  hypothesis break  with  that  down  a b i l i t y  of  larval  limits  of  food  should  be  mortality  survival  has Tyria  is  acting  low  that  after  regulate yet  to  and  of  an  may,  when  high,  act  to  stimulate outbreaks mortality,  Data  on  Tyria  geographic  areas  area  had  a  data  strengthen  larval  dispersal  is  populations shown.  populations  was  plant  Tyria  dispersal  be  larvae  was  to  each  these  effect  Table  when  dispersal  since  the  2  dispersal  Although  when  from  m .  climatic  regulatory  obtainable  per  of  survival  63%  a  plant  in  There  populations.  any  supply  28.  plants  prediction,  to  Fig.  predicted  different  dispersal  larval  of  per  such  which  and  to  with  could  given  at  at  dropped  example  is  rate  plants  changing  25%  instead  jacobaea.  How  from  dispersal  ragwort  this  S.  in  5  success  value  with  size  larval  associated  this  2  20%.  daily 19  0.5  therefore  high-density  consistent  w i l l  I  The  that  increase  to  2  At  A hypothetical  given  to  and  m  associated  mortality  5.0  low  per m  their  density.  population  equation  growth.  with  high the  is  per  Table  suggests  population  outbreaks were  data.  from  plant  size?  f i e l d  population  result  population  plants  from  experiments  1 plant  on  the  density  depress  at  density  on  decreased  This  with  mortality,  taken  in  f i e l d  population  based  disperse  but  0.5  dispersal  of  i t  at  in  varied  plants,  and  density,  i.e.  plants  found  change  25:  released  in  high, below  Such areas  the the  evidence of  low  207  TABLE  25^  E f f e c t of dispersal mortality on a hypothetical population of f i f t h - i n s t a r larvae. Dispersal rate is 0.12 moves/larva/day.  End of Day:  NUMBER 5.0  0 1 2 3 4 5 6 7 . 8 9 10  OF  plants/m 1000 971 943 916 890 864 840 816 793 770 748  \  FIFTH-INSTAR 2  2.5  LARVAE  plants/m 1000 950 902 857 814 773 734 697 662 629 598  ON 2  SUCCESSIVE 0.5  DAYS  plants/m 1000 904 818 740 669 605 547 495 448 4 05 366  2  208  jacobaea of  density.  fluctuations  low  ragwort The  Tyria  density  patchy  persistence Tyria  in  Other  factors  numbers  than  in  of  the  density  i s  extremely  overloaded,  a  These  w i l l  become  The  dispersing  plants  defoliated. have  adeguate  larvae  w i l l  in  An  (L.),  excessive  for  spring  the  have  it  of  been  a  of  codling  but  does  laid  random  rather  than  uniformly.  the  escapes  second  generation  overwintering analagous  to  starvation  by  Monro's success  of  attack  larvae. those locating  (1967)  by  not  the  When  plants eggs  w i l l  The  second  few  dispersing  l i k e l y crash  l i k e l y  because small  some  occurs. (1964) Cydia summer.  destroy  the  the  eggs  are  fraction  of  generation these  the  that  Geier  could  is  found  by  provide  the  moths  are  generation Tyria  are  Thus  per  so  them.  plants  them  by  are  on  generations  and  the  larvae  that  avoid  refuge.  explanation  Cactoblastis  reason.  moth,  f i r s t  moths,  food  the  codling  moth  do  Thus  a  i t  local  two  crop,  that  find  the  f r u i t  f r u i t s  no  for  other  described  entire at  as  makes  when  completes  density  important  or  with  density.  most  few  magnitude areas  development.  distribution  has  is  that  their  in  ragwort  and  larvae  pupation  lower  the  following  refuges'  populations where  high  high  'food  strategy  Australian  pomonella  to  of  equal,  be  clusters  w i l l  for  egg  survive  A comparable for  plants  food  heterogeneity  of  population  few  should  areas  distribution  being  cactorum  for on  the prickly  rapid pear  spread was  that  and the  209  regulation  imposed  ineffective  in  destroyed  would  could  i t  easily  only  proposed are  is  to  sedentary strategy  a  that  and  is  more  generations  per  the  of  like  plants  by  f i r s t  second  generation.  become  that  larvae.  of  and  In the  the  generation  this  and  this  the  and  extent  Cactoblastis  be  when  larvae  plants  of  as a l l  plant  in  the  are  more  than  the  moth,  u t i l i z a t i o n  would  larvae  however,  regard  codling  was  separated  Tyria  host  plant  the  ineffective  differ,  be  would  To  Tyria  would  regulation  were  in  unoccupied  and  The  mortality.  both  larvae.  summer,  source.  plants  the  When o n e  neighbour,  species  u t i l i z e  Cactoblastis  i t s  high  they  egg-sticks  cactus.  mechanisms  These  a b i l i t i e s  of  of  food  when  suffered  high.  find  on  new  self-regulating  dispersive l i k e l y  collapse  larvae  in  clumping  stands  effective  similar  density  the  dense  reach  become  dispersing  by  are  the  Cactoblastis it.has the  deleterious  two cactus  to  the  210  GENERAL  DISCUSSION  "Stability lies i n the a b i l i t y to in the a b i l i t y to hold tenaciously taken or numbers once achieved."  bounce back, not to ground once  F.W.Preston,  Previous §§a§cio and  jacobaea,  the  and  effects  food  these  studies  on  "bounce  back"  chance  and  (1971)  found  that  dependent  manner,  may  l2£i§.  i  the  crash  thus not  increase  become  more  the to  stable  local  after  1971).  so  populations  to  as  a  matter  of  limits  of  Dempster  controlling  inversely  an  In  fluctuated  i n s t a b i l i t y . the  time  parasites,  conditions.  an  plant,  over  Meijden  largely  in  host  numbers  incapable  acted to  der  of  viewed  were  adding  in  its  predators,  extrinsic  predators  and  populations  a b i l i t y  was  parasites  do  or  a  of  1971; van  Tyria  that  moth  changes  growth  prevailing  while  supply,  studies  after  numbers,  populations  the  (Dempster  abundance  the  cinnabar  population  particular in  the  described  shortage  widely  on  1969  densityYet  of  other  their  food  outbreak  (Hawkes  monophagous  and  several  and  association  1973).  adaptations S.  jacobaea  ability larval  to  essentially  s  that -  suggest the  sequester  feeding,  ovipositing  adults,  a  long  cryptic  effect  host-plant the and  of  the  alkaloids,  accurate the  intimate  larval the  selection  has  with  colours,  the  specificity  of  of  by  synchronization  ragwort of  larval  211  development obligatory this  to  the  wide  of  fluctuations  In both  the  the  moth  on  appears  the  in  consistent  may  with  individual.  these  the The  are  concur  mechanisms  behind  by  view  of  traits  of  is  risk  have  low. of  density  is  natural  to  their  that  behavioural  i f  fluctuations  at  two  low  that  findings  are  to  the  numerical  studies  so  acts  on  elucidate  numerical to  Tyria  essential  selection  workers  individuals)  (1971)  These  the  positive  extinction  and  that  a  Therefore  an  when  that  behavioural  places  due  population  prevent to  proposed  behaviours  previous  l i k e l y  counts  have  extinctions.  of  the  appeared  behavioural  density  paradigm  was  Watson's  supplemented  local  f a i l u r e  primarily  with  high  an  was  to  self-regulatory  the  supply,  cause  mechanisms  (data  be  c r i t i c a l  which  density  reducing  when  lack  by  Against  association mechanism  and  same  when  aided  comm.).  no  on  have  these  is  extinction.  stages  fact,  rate  of  resource  a  local  larval  in  growth  phases:  events  of  which  pers.  had  numbers,  addition,  capable  Tyria  concentrated  and  c r i t i c a l  chance  I  does,  In  cycle,  evolutionary  that  in  study  adult  mechanisms. effect  long  likelihood  this  cinnabar  the  a  contradiction  increase  l i f e  (B.J.R.Philogene,  diapause  evidence  apparent  plant's  approach  problem.  studies the are  I  should  underlying to  be  understood.  In some  the  following  behavioural  t r a i t s  paragraphs of  Tyria  I  summarize that  the  affec/t  actions  of  population  212  dynamics.  Other  mentioned shall  only  behaviours,  b r i e f l y ,  understand  their  reference  w i l l  pressure,  the  parasites;  none  extrinsic  factor,  general and  role  w i l l  complete any  could  that  make  were  S.  far  number  I  concluded  larvae have  by  concerned  of  restricted factors  with  or  several  predation role  does  of One  play  a  populations,  approach  prevented  mortality a  s t a b i l i t y  more  and  a in  general  in  detail, outbreaks  evidence. in  L i t t l e  the  relationships  numbers common  Tyria  adopting  about  we  measured.  affecting  by  before  as  jacobaea,  independent limit  such  sites,  S.  dynamics  predictions  w i l l  of  be  abundance.  s p e c i f i c a l l y  Instead,  investigating  relationships so  major  needed  w i l l  Clearly,  particular  properties  of  behaviours  that  habitats; Tjria  and  have  been  populations.  a  plant  usually  the  general  was  in  given  of  is  factors,  pupation  density  My  work  dispersal,  determining  were  population  adult  further  of  habitat.  by  in  as  extrinsic  discussed.  factors  jacobaea  studied  the  supported  study  The  to  these  the  analysis  particular this  made  of  in  be  and  role  importance  particular  approach I  be  since  such  lay  of  are  between  shown  clusters, that  since  surviving  from  the  sufficient  food  on  development.  Under  probably  f l y  one  Figure  averaging  moths they  only  in  the  before  cluster  31.  Females  30-50 lay and  per  only after  day.  average-sized their  conditions  o r i g i n a l of  LOW  eggs  I  lay per  one  LARVAL  eggs  cluster,  cluster  on  oviposition, estimated  cluster host  their  would  plant DENSITY  to  that  and any and the  usually complete (Fig.  31)  213  therefore, that  only  i.e.  few  the a  few  and  dispersal  rates  any  a  years  is  YEARLY  as  INCREASE  commonness many  were  frequently  part  from  When  to  and  31  by  cluster  size  vegetative laid  on  sufficient  of  i t s  cluster  of  a  large  reaches  HIGH  DENSITY  tends  to  new  'backfire'  plants  population egg  now  size.  in  and  plays  successive labelled  form  of  S.  the  an  Larvae  since  a b i l i t y  important  on  rosettes that  egg-spacing  the  on  jacobaea,  plants  had  strategy  of  larvae in  the  females  continue  to  to  plants  eggs,  thereby  increasing  the  overloaded  plants.  As  oviposit  resulting  of  however,  f a i l  females  dependent  rosettes.  Although they  part  carry  the  clusters  was  clump  Tyria  plants  for  c i r c l e  already  large  not  promote  own  on  is  spacing  their  on  guality  resource  spread  laid  be  food  growth  small  food,  crown.  of  rates  small  root  to  dispersal  growth  central  disperse  w i l l  density-dependent, plant  use  the  overloaded),  of  Continued  a  females  maintenance  size  is  ensures  crowding  effect  on  Tyria  (are  Larval  (The  effective  Fig.  of  were had  the  in  food.  disperse  female  eggs  dispersal  increase.  the  often  developed  of  by  NUMBERS.  of  clusters  to  many  low.  cluster  of  IN  be  makes  adaptiveness  rosettes  of  rate  too  larval  Tyria low;  clusters  short  also  represented  The the  w i l l  is  positive  be  tendency  Thus  density  w i l l  of  have  since  innate  known.) when  plants  larvae  uncommon,  and  spacing  cluster  avoid  role  proportion  of  which eggs  preferentially  distribution  is  214  FIGURE  31  Flow diagram processes that dispersal has magnitude of i t s  indicating the affect numbers been omitted e f f e c t s are not  major behavioural in Tyria. Adult as the point and yet understood.  214  LOW L A R V A L , DENSITY  Starvation following o u t b r e a k and d e f o l i a t i o n  Little overloading E x c e s s food Low d i s p e r s a l r a t e  DECREASE IN N U M B E R S Dispersal mortality low  D i s p e r s a l mortality is high  HIGH L A R V A L DENSITY  O v e r l o a d i n g and c r o w d i n g , .-.high d i s p e r s a l r a t e i n t o a r e a s of••  HIGH PLANT DENSITY  Defoliation  . New growth  V e g e t a t ive reg rowth  REDUCTION J|HN DENSITY W e a t h e r and compet it ion  LOW PLANT DENSITY  a  215  contagious, overloaded much  of  which  further  plants. the  Consequently  food  density-dependent during  the  hence  two  larval When  before This  in  density  that  plants of  f i f t h - i n s t a r extrinsic  at  behaviour,  larval  dispersing  further  INCREASE  IN  §•  jacobaea  ragwort  such  larvae  for  eggs  on  the  and high,  particularly  as  w i l l  with  S.  some  success  1 per  be  predators  or  summers  w i l l  that  density  egg  d i s t r i b u t i o n , and  the  biomass  and  larval  dispersal  increase,  w i l l  and  density  is w i l l w i l l  to  an  pressure in  the  on  local  mortality  further  the  therefore  again  defoliation  of  i n t r i n s i c  mortality,  leading  such  an  but  of  point  the  various  less  growth,  the  to  far  the  at  on  suffer  population  reduce  larvae  and  plant  Dispersal  this  of  population  by  supply.  At  supply.  desiccation,  food  NUMBERS.  food  2  i f  I  density  due  regulated However,  high,  lower  m ,  natural  31:  density.  mortality to  a  Fig.  jacobaea  low  in  density,  in  local  w i l l  be  plant  the  below  observed  nature  the  of  the  densities I  low  reduced  on  dispersal.  population,  subseguent  not  of  starve  larvae,  rises  or  l i m i t  ultimately  of  may  i t  dispersal  Mortality  contagious  promote  would  represented  high  be  based  larvae.  more  were of  are  and  can  dispersal  u t i l i z e  proportion  larvae  larvae  absolute  factors,  the  rate  of  low  plant  w i l l  reduce  areas  is  population  high,  many  wasted,  outcomes  i s  the  prediction  rate  of  numbers  reaching  finding high  success  contrasting  plant  be  the  instar.  dispersal  predict  would  dispersal  f i f t h  Dispersal  increases  in  population  216  growth  w i l l  In  be  some  (1971)  of  starvation  of  by  Adult point  of  occurring density.  (Fig.  2)  hindered  larval  apply  densities  Bragg,  hindrances play  an  dispersal the  to  does and  the  to  new  persistence  to  rate  adult to  by  of  food  maintained  than  outbreak and  that  would  in  continued  an  suggest  be is  weak great  the  t a l l  at  of  severe outbreaks  occur  through  simply  because  effect  (1971) is  trees but  and  at i t  in  l i m i t i n g  habitats  is  l i k e l y  of  species.  At  have  to  population unlikely  prevent  outbreaks  surrounding  Pylon  where  outbreak  role  myself  seems  same  Although  not  low  the  open  are  density-dependent,  than  enough  The  31  its  f l i e r s ;  Power  extremely  dispersal.  the  of  high  dispersal,  an  Fig.  dispersal  attained.  is  in  Dempster  at  adults  were  appear  Both  Possibly  of  halted  I  magnitude  adult  appear  important  31  density  not  frequently  adult  Fig.  be  Dempster's  circumstances  shortage  lower  that  C a l i f o r n i a ,  w i l l  as  dispersal.  dispersal  occurring.  not  a  certainty.  from  did  to  action  Females  such  In  such  density  eventually  larvae.  larval  more  their  In  absolute  most  evidence  habitats,  plant  is  dispersal  with  indirect  that  an  numbers  regulation  known  plant  Heath,  increase  through  reduce  stopped.  defoliation.  population Tyria  or  favourable  Weeting  spite  i t s  slowed  area adults  local  Field  restriction egually  area  high  at  without  Fort  physical  probably  don't  populations,  major the  Top  their  importance  moment  there  are  for no  217  published of to  new  data Tyria  assess  the  persistence  populations, importance  but  of  local  of  environmental  abundance  of  populations  primarily  Boer  over  Andrewartha  importance  (1968)  and  at  the  as  reducing  the  the  of  absence  contention. cycle  that  possibly 1«  Period  early of  I  as  60-odd  capable  the  of the  adult end  Schmidl  caged  in  adults  spread  over  emergence moths,  April  The  guantified.  the  actual  Victoria, in  days.  period  discriminate  and  (1972b)  emerged 51  develop  stressed  i t s  of  numbers  and  Whether  of  such  growth  in  a  of  point  Tyria's  l i f e  heterogeneity  River  occasionally  into  July,  a  pattern  emergence  emerged  of  from  1000  and  that  over  density  late  noted  although is  offspring  emergers,  high of and  not  field15%  emergence an  as  spread  was  emergence  period,  the  and  population. Chase  larval  favour  both  concept  remains  features  whereas  at  studied  against  by  population  factors  Adults  20-day  When  w i l l  the  Australia,  a  area.  debated  his  extinction.  the  determining  s t a b i l i z i n g animal  some  of  emergence.  of  or  within-population  persistence  days.  pupae  to  been  (1954)  regulating  below  contribute  to  to  density-dependent  summarize  long  in  are  to  geographical  Birch  of  of  relative  heterogeneity has  of  likelihood i s  larger  we  variation,  of  heterogeneity  a  if  heterogeneity,  'spreading  way  needed  level,  populations a  are  establishment  inter-population  between r i s k '  data  of  extinctions  and  the  invoked  frequency  such  role  within  species  the  the  ecologists.  den  estimate  of  The the  which  of was  extended  first-emerging increase  the  218  probability  of  some  pupation.  Emergence  moisture  conditions,  due  to  differences  or  to  differences  2.  Size  guite  of  egg  size  patterns.  proposed  to  The  number  female, of  reduce i f  (Part  might II)  to  eggs  per  in  part,  to  to  a  cues,  cluster the  was  at  female's  reducing  is  change  highest  from  at  least  amd  low  laying  both  related the  in  weather  medium  be  be  sites.  appeared,  therefore  for  could  short-term  larvae  of  for and  these  pupation  clusters  any,  emergence  of  and  food  temperature  pupae  overloading  clusters  strategy  in  at  young  smaller  by  between  owing,  advantages,  large  variability  microclimate  of  sufficient  triggered  sensitivity  clusters,  The  and  the  survival  theoretically,  small  so  Tyria  age  obtaining  probably  the  in  While  densities.  in in  with  average-sized  is  clusters.  variable  cluster  larvae  to  the  amount  of  overloading. 3«  Distribution  distributed  in  with  of  much  of  a  contagious the  choosing  certain  on  rosettes  small  on were  plants more  difference this  in  the  as  within  other  than At  cluster  Clusters in  four  being  the  oviposition  projected  size.  above  small high  pasture  plants, larval  plants.  of  clusters Larval  of  Tyria  f i e l d  were that  Large  two  noted. were  mortality  females  were  allowing  densities  were  laid  freguently  herbs.  even  of  Eggs  less  eggs  populations,  result  sites.  vegetation  distribution  proportion  overloaded  manner  contagion  plants  attractive  contagious  increased on  that  egg; c l u s t e r s .  plants  for  the  effects  of  First,  it  estimated was  than  to  higher  be on  219  overloaded  than  on  non-overloaded  contagion  of  larvae  acted  reduce  the  population  growth  similar  situation  a  However, effect could  i f of  be  between were  dispersing a  effect  of  plants  was  provide  of  as  densities density  f i e l d **•  by  reduced  the  f i e l d ;  some  as  long  or  4  times to  has  described  Cactoblastis  cactprum.  (1967)  l i t t l e  mortality  on  the  to  the  growth  to  10 in  be  dispersers  and  dispersal,  such  strategy.  plants  that  days, the shown,  of  simulation to  and  rate  most  from  of  a  the  could  overloaded  heterogeneity  runs  plants  escaped  consequently  population  of  crashes  computer this  Fifth-instar  crowding  overloaded,  while same  several period.  that  could  Given be  and  be and  larval  for  high  model.  effect  larvae  in  An a  differed  defoliation  in  nearly  defoliated  larvae  changed  It  single  non-dispersers. production  densities  4) .  to  on  when had  investigate  crowding.  response  larval  refuges*  dispersing  made  in  'food  between-plant  was  remained as  v a r i a b i l i t y  females,  (Appendix  their  for  Monro moth  magnitude  in  response  in  remains  This  attempt  experiment  greatly  the  manner  distribution  were  larvae  populations  Larval  risk*  Refuges  plants.  unsuccessful  to  the  ovipositing  food  defoliated  hence  density-dependent  suffer  larval  and  small.  overloaded.  used  the  second  attention  a  rate.  larvae  contagious  quite  The  for  in  plants,  is  possible,  females the  viewed  plants  plants but  produce  uncertain as  the  a  s t i l l both  success  'spreading  3  of of  220  I that  have  are  host  summarized  beneficial  plant,  i.e.  coevolution as  these  the §•  given  the  adaptations of  jacobaea.  pressure?  both How  I  defoliation  a  the  number  host  that  Tyria  vegetative the  as  a  recovery  the  plant's  and  S.  a  Raven  1964).  they  respond  to  of  i t s of  Inasmuch  w i l l  do  so  at  biomass  this  jacobaea's  strategy,  Tyria  period  reproductive  plant  in  characterstics  numbers  and  characterized  adaptations  indicate  (Ehrlich  increase  does  of  particular  adaptations  with  expense  above  of  selective  response  not  as  a  to  resistance  ( strategy,  since  detrimental either  guickly  perennial The  form  and  history,  as so  respond  is  of  have  a l l  in  seed  one  either  the  produced  of  in  more that  S.  of  or  the  seed  in  become  not  both.  stems,  stages  plants to  did  did  or  present  a  both.  o r i g i n a l  seed  average  defoliation  the  population  perennials,  feature  and  or  than  post-pioneer a  not  switched  summer,  jacobaea's.  crop  rosettes  or  repeated  of  are  Defoliated  perennials  was  fashion,  growth  size  a b i l i t y  ragwort  crop  following  suggested  evident  in  seed  10%  proportion  responses  Discussion).  the  was  plants  second  only  obvious  second  competitive  it a  produce  populations  I  heterogeneity  produce  plants  the  the  a  crop  data  persistence  Just  may  Field  through  (Part  flowered  seed  increase  prolong  may  and  perennial  biennials. would  Tyria produced  secondary  crop,  and,  to  most  thereby  communities. in  Tyria's  Defoliated perennial, Also, both. each  l i f e plants  or  they  perennial  Thus summer,  ragwort which  221  might  act  as  environmental effect,  a effects  and  on  infested the how  most  rosettes  important  this of  stands  of  the  plants  response  adaptations  to  the  habitat,  not  as  that  in  yellow  i t s  The  role  expressed  by  and  invertebrate adult  and  numbers,  specific  and  that  plant  growth  and  forms  oviposition moderately may  summer. buffer'  provide  Finding  out  is  the  to  experiments types  adverse  in  were  which  subjected  in  were  nature  the  of  cinnabar already  defoliation  viewed the  adaptations  those  to  faced  and  the  primarily  plant's  moth  behavioural  regulating  population  ecologists  wonders  species.  there  to  i n t r i n s i c  vertebrate  larval  jacobaea  as  sand  dune  defoliation adds  by  no  by  selection  tansy  ragwort  community.  that  one  S.  response,  from  dune  belief  important  1967),  differ  of  unstable  suggested  forces  such  are  undamaged,  require  adverse  stress.  that  I  stems  'population  single  one  between  following  would  mixed and  in  J-iria.  the  postulated  f l e x i b i l i t y  and  When  remain  populations  environmental Both  w i l l  i s  these  disparity  stems.  against  Tyria  attack  the  and  seed-producing  ragwort to  witness  buffer'  1967).  indeed  rosettes  persistence  (Harper  does  d i f f e r e n t i a l l y ; rates  'population  I  how  have  is  evidence,  an  has  been  (Wynne-Edwards  1962;  Chitty  common  in  play  size  suggested  behaviours  mechanisms  such that  Tyria  presented  mechanisms a  may  are  combination act  below,  to that  in of  regulate other  222  insect  species  features  of  regulation 1.  The  2.  food  3.  Food  may  to  units.  occur;  is  species  disperse  between  overloading, larval  as  stages  larvae  mortality, fighting  to  occurs  possible,  in  as  food  to  is  in  system terms  as  particular  that  promote  follows.  distributed  during  discrete from  one  in  a  contagious  units,  food  overloaded,  other  such  unit  and  as  to  a  that  another.  conseguence  units.  dispersal  conditions  when  The  resource.  moving  these  food  to  sparsely  regulation  units  are  dense  distributed  is  hypothesised  this  regulatory  ineffective. rely  on  them. the of  and a  general  become  high  be  in  when  may  Under  w i l l  Many  between  die  fashion.  jacobaea  occurs  conversely  mechanism  the  the  disperse  Mortality  food  to  units  similar  population  resource  individuals 4.  stated  herbivore relative  in  Tyria/S.  can'be  individuals  ,  the  manner The  behave  discrete In  these  codling many  moth  insect  reduction  less  frequently  exemplified  by  units  species  the  and  (Geier  parasites,  leads  density, level.  when  Severe  to  and  other  moth  Cactoblastis  of and  fighting in  situ  intra-specific  successful the  1964)  through  Tyria  cannot  occurrence  larvae  of  non-overloaded  food  dispersal species  is  listed  below. The appears been  to  ecology  of  follow  the  discussed  in  the Tyria  detail  in  pattern Parts  II  (Monro and  cactorum,  1967), III.  has  which already  223  Carne sawfly  (1965,1969)  Perga  relevant  a f f i n i s  points  contagiously;  carried  a f f i n i s  of  his  female  sawflies  narrow  leaves  of  young  the  broad  leaves  of  mature  as  a  the  colony,  sometimes  colonies  s t i l l  had  compact  they excess  colony  successfully ground that  or  inter-tree  A l l  the  identified, plants.  with  The  exact  outbreaks  is  does  (1965)  in  state stands  predict, In  the these  long-term  clear that  the  from  the  two  study  by  I  during  albitextura  when  then  trees  Carne's was  except  Carne  of  host  trees as  a  colonies on  bare  concluded  starvation  during  mortality."  system  tree  can  for  be  ragwort  density  publications  which  and  although  "consistently  density,  fed  before  dispersed  10'-15'  he  numerous" would  be,  I  situation.  have  attributed  larval  dispersal.  1963,  suggests  which  "Few  and  into  larger  substituted  between  (1962,  than  trees.  jacobaea  host-density  examples  Clark  fed",  source  low  into  "...long  pastures."  Tyria/S.  or  trees  larvae  sawfly  intermediate  most, s t a b l e  small  exceeding  relationship  incurred  Cardiasjiina  of  oviposit  larvae,  other  major  laid  Hence  "desiccation a  were  trees  the  the the  Eggs  to  of  and  eucalypt  f u l l y  of  eucalyptus  not  of  mortality  was  features  easier  level  densities  dispersal  i t  The  distances  hard-grazed,  high  found  were  search  moved  on  at  in  follows.  defoliated  study  (Hymenoptera), as  trees.  foliage.  extensive  are  (small)  supported  an  Kirby  study  the  out  that  1964)  regulation Evidence on  mortality  the during  to  from  a  Psyllid adult  224  dispersal  may  contagiously  act  in  the  on  the  laid  eggs  Overcrowded  nymphs  died  feed  leaves  survival yards.  i f  (Clark  from few a  high  -  of  and  gum  density  of  Cardiaspina  plant at  unless by  numerical  on  the  the  distribution of  data,  regulation or  and  of  numbers,  common. by  the  of  is  through  practical  of  low  chance  greater adult  a  and  of  than  130  dispersal  and  violent  more  stable  Clark  (1964)  density  of  of  the  psyllid  competition  unable  to  of  s t a b i l i z e  the  wind  for  psyllid  is  force."  defoliating  insects  have  extrinsic  factors  on  made  progress  on  and  d i f f i c u l t  Collection  low  between  a v a i l a b i l i t y , i t  on  have  interactions  a  Adults  s t a b i l i z a t i o n  density  studies  and  to  were  maintained.  dispersal  influence  fluctuations,  elucidating  inhibited  population  tree  had  intraspecific  effective as  to  density  be  the  The  able  few  prolonged  relatively  for  as  high,  were  although groups.  clearings  processes...are  factors  other  a  (1963)  (1962).  was  distributed  scattered  had  plant  could  levels.  the  such  concentrated  paucity  that  associated  Many  rare  mean  distant  trees  lower  reguired  high  and  limited  is  shortage  cross  were  trees in  outbreaks  of  seems  food  to  areas  " . . . i t  gum  conseguence  attempted density  Eggs  or  feet  In  numbers  i s  as  of  singly  1964).  numbers food  and  the  was  concluded host  a  they  When  success  high  only  regularly,  manner.  leaves  individuals  reach  same  less  dispersal, mortality. to  Given  determine  the  mechanism  the  appropriate  d i f f i c u l t i e s  resource  i f  outlined data  associated  the the  above,  has  been  with  the  225  study  of  dispersal, and adult  adult  dispersal.  rather  than  larval  behaviour  behaviour.  undertaken  in  through can  regulation  adult  usually  Hopefully  future.  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Ascolcus Zool. 9:  dispersion in relation B o y d , E d i n b u r g h . 6 5 3 p.  to  235  APPENDIX  1,  I  spent  population to  Estimation  have  confounded plants. from use  details  egg  Pylon,  July,  1969. eggs  after In  on  1969  Power  densities this  3.483) hot  the  end  larval  Power  Pylon  losses  was  values  end  8.2%  have  in  instars  defoliated of  survival  instar,  survival  for  were  many  larvae  feeding.  These  survival  died  Top  and  I  as  I  present  many  through  figures  are  was  June  and  plants  and  egg  survival  low;  Excessive  97.3%.  a  were  egg  22.9% or  lower  41.25 and  period  considerably  Power  eggs  of  per  (S.E.  =  unusually  hatching,  desiccation,  with  at  42.79  in  larval  associated  much  (n=138) ,  eggs  Field  in  98.4%.  instar  was  plants  predation,  similar:  There  22  during  Field  after  i n i t i a l l y  Field  (n=43).  Top  main . f a c t o r  were  Top  when  believe  In  Pylon.  the  Field,  larvae the  f i r s t  Power been  Top  9 9 . 7 % and  the  sizes  Pylon  June  plants.  were  densities  = 2.777)  in  9 8 . 6 % and  of  in  cluster  Power  from  only  derivation.  on  as  the  Pylon  f i f t h  third  the  eggs  not  and  of  5730  the  Power  estimates  calculate  counted  to  recording  useful  and  Egg  weather  obtain  eggs  could  for  dispersed  a l l  and  cluster(S.E.  had  censused  mortality  Pylon.  that  and  the  and  fourth  plants  the  1969  Field  30  Pylon  Field  Top  selected  Survival Top  in  in  I  s t e r i l i t y  power  time  the  to  to  Survival.  for  did  their  I  on  I  stage  values  here  In  Tyria  larvae  Nonetheless  these  1820  of  estimates by  the  Larval  considerable  dynamics my  of  often lower  and  I  before than  236  those By  reported  contrast,  eggs  by  1668  (43.3%)  Dempster  (1971)  f i r s t - i n s t a r  in  Top  Field  and  van  larvae  during  der  Meijden  survived  studies  in  out May  (1971). of  and  3854  June  of  1971.  To  calculate  from  the  Pylon  data.  during close at  1969  third  those  Monks  data  Survival  the to  third  instar  instar  84.1% for  pattern  His  starvation  effects,  survival  8 5 . 6 % as  I from  then  egg  through  the  (1)  10.4%  (2)  15.3%  596  to  the  and  (1)  is  fourth  based  fourth-instar  (1971)  from  and  showed  that  that  the  have  in  River  for  the  different  population survival  69.1%,  and  for for  85.1%. survival  in  instar  that  the  fourth  and  extremely  a  populations,  used  Power  61.4%,  third  assumed  and  a  and  86.2%,  instars  are  61.5%,  therefore  two  values  61.0%,  Chase  survival  was  instar  to I  Field  second  81.7%,  close  Top  instar  These  third  for  also  calculated  Estimate where  we're  years).  apply  85.6%.  and  the  second  Dempster  were  very  second  combined  figures  figures  three  the  the  was by  years  was  would  of  during  survival  Dempster's  for  have  instar  Wood.  consecutive  =  I  measured  three  fourth  survival  the (mean  similar excluding  third  instar  instar.  estimates  for  survival  instar.  on  the  larvae  1969  data  survived  from from  an  Top  Field,  i n i t i a l  egg  237  count  of  Power low  5730.  Pylon  I  data  f i r s t - i n s t a r Estimate  survival out  in  of  1971,  larvae, fourth  instar from  somewhat  based  in  assumes  part no  five  13.8% for  comparable  because  of  the  1971  the  on  35.0%,  egg  to  a  plant.  thus  fourth  values  from  10.2%,  8.0%,  arbritrary Chase  mortality  the  figure  from  the  uncharacteristically  River from  (2).  egg  of  Mean  to  the  each  giving  of  f i r s t  instar  experiment  carried  20  survival an  f i r s t - i n s t a r through  estimate  to  of  the  15.3%  instar. 3  years and  survival  survival  estimate  results  replicates,  was  egg-to-fifth-instar and  with  placed  on  the  combines  when  are:  use  survival.  43.3%  Comparable population  not  (4.5%)  (2)  were  survival  a  did  of  12.8% of  data  and  of  for  (Dempster  90% f o r  starvation values  data  the  Dempster or  the  Monks  1971). f i f t h  for  This  estimate  used  instar,  (1971)  parasites.  9.3%  I  Wwod  that gave (1),  238  APPENDIX  2.  Determination  Larvae cm  high  or  two  Larvae or  and  were  feeding.  16  groups  small,  used  of  of  the  five.  singly.  instars  leaves were  the  were  i s  to  and  kept  10  third the  the  95%  container  in  fourth  vial  and  larvae data  grams  that  they  confidence  one,  two,  and  after  by  through larvae.  were  reared  were  divided  into  larvae  were  prior  their  to,  fourth  larvae  weight,  one water.  occurred  died  food  14  conditions,  instars  average  with  every  f i f t h  for  wet  placed  before  larvae  Forty-two The  I  consumption  when  Instars.  containers,  identical  weight the  by  f i l l e d  weighed  under  instar,  feeding  in  plastic  containers  second-instar  pupation. below  and  adjusting  discarded.  given  deviation  In  each  were  change in  Consumption  stoppered  Twenty-one  and  successfully  of  In  leaves  leaves  groups  pupation,  instar  a  The  was  beginning  reared  in  fresh  Food  ventilated  diameter.  proportional  uptake  in  in  given  Control  Eight the  cm  raised  days.  the  water  9  leaves  three  and  were  of  u n t i l  or and  f i f t h  were consumed  with  the  at  reared by  each  standard  limits.  Instar II III /  IV V Thirty  immediately,  0.045  (0.009)  (0.038  -  0.053)  0 . 115  (0.019)  (0. 105  -  0.126)  0.417  (0.140)  (0. 373  -  0.461)  3.515  (0.822)  (3.260  -  3.772)  leaves and  were  oven-dried  cut at  from 80  C  living until  plants,  further  weight  weighed loss  239  was  negligible.  5.50 to  a  :  1,  in  weight  For  the  Many  with  unusually  high  average normal  The  and  12.1  8-10  days. those  in  Estimates as  reliable instar  of  follows.  a  the  an  same  dry  the  and  the  weight  was  above  values  for  f i f t h  value  estimate rearing  or  the  died  weights  of or  is  the of  I  pupae  the  42  pupae  weights  of  129  mg  (S.E.  mg  (S.E.  =  2.4)  the  were  was  much raised 202  = 3.3)  for  an  than  pupae  of  been  spent  longer  weight  130  were  have and  other  The  used  may  usual,  from  virus.  larvae  which  sample,  consumption  polyhedral  than  instar,  of  room  consumption  larger  the  with  food The  of  f i r s t  5  dry  from wt  raised  for  and  168  to  the  at  mg for  pupae  four  therefore  C.  the  more  third,  and  fourth  value  for  f i f t h  are  40±5%  26.7  are  probably  second,  data  18.3  larva  (1972)  Isaacson's  temperatures g  for  Isaacson's  larvae,  per  estimate,  values  and  light,  0.440  consumption  my  each  was  to  convert  suggests  much  mean  consumption.  larva  as  food  field  replicates,  per  to  believe  the  (33%)  in  The  uses  consumption,  and  weight  f i e l d .  of  one,  instar  in  grew  pupae, the  I  high  their  compared  lab-reared  too  Finally,  laboratory.  derived  reasons  days  in  collected  used  larvae  = 4.7),  wet  microsporidian  than  35  was  larvae  greater  (S.E.  value  mortality  of  the  of  was  a  infected,  abnormal.  ratio  following  f i e l d .  infection  mean  measure.  consumption  the  also  this  dry  instar /  and  The  based  R.H., Food  instars.  16  on  40  h  of  consumption The  second  240  estimate be  uses  considered  consumption below  in  g  my as  of  f i f t h an  consumption  upper-limit  0.744  dry  instar  g  per  value.  larva.  Both  figures,  This  estimate  sets  of  wt.  SOURCE Green  OF  DATA  Combined  Isaacson  Instar II  0.008  0.008  —  III  0.021  0.021  0. 015  0.076  0.076  0 . 070  0.639  0.335  0. 335  0.744  0.440  IV V  Total  data  and was are  should for  a  listed  APPENDIX  3.  Dispersal rates of fifth-instar larvae ages to adjacent plants. Dispersal is via overlapping leaves.  Days Present  No. of Larvae  No. of Moves  1 2 3 4 5 6 7 8 9 10  39 66 78 57 32 61 50 26 12 6  Moves/ Larva  1  ORIGINAL  of different assumed to be  Moves/ Larva/day  2  COHORT  0 10 12 13 4 18 20 10 4 1  0.00 0.15 0.15 0.22 0.12 0.29 0.40 0.38 0.33 0.16  0.00 0.15 0.08 0.07 0.03 0.06 0.07 0.06 0.04 0.02  0.00 0.06 0.23 0.22 0.00 0.00  0.00 0.06 0.12 0.07 0.00 0.00 0.02 0.07 0.06 0.00  RECRUITS 1 2 3 4 5 6 7 8 9 10  12 16 26 9 2 10 15 6 7 0  0 1 6 2 0 0 2 3 3 0  0.-13  0.50 0.42 0.00 continued  on  next  page.  242  Appendix Days Present  3  cont.  No. of Larvae  No.  of  Moves ALL  1 2 3 4 5 6 7 8 9 10  See  54 83 111 70 41 74 68 41 19 6  Table  20  for  0 11 18 15 7 19 23 15 7 1  footnote  1  Moves/ Larva LARVAE  Moves/ Larva/day  3  0.00 0.13 0 . 16 0.21 0 . 17 0.25 0.33 0.36 0.36 0.16  explanations.  0.00 0 . 13 0.08 0.07 0.04 0.05 0.06 0.05 0.05 0.02  2  243  APPENDIX  4.  The  focus  populations when  mean  are  of  behaviour be  the  and  It  is  the  overloaded, some  plants  as  plant  in  under  these  to  larval  dispersal  refuges  and  be  to  only  rates  w i l l  these  dispersers, on  plants  which  to  combine  was  random  larval  treatments to  be  my  serious  Design  no  low  index  measuring  of  the  was  and  plots, m x kept  2  of  four m,  short  were  larvae  escape  high  plant to  highest  the  into  inevitable these  food  addition, then  swamped  not by  themselves  design  therefore  with  of  uniform  and  combination  of  pupae.  population the  females  next  This  to  was  survive  generation.  Experiment  measuring marked  during  a  the  find  which  proportion of  persist  My  plants  high,  being may  most  in  are  assume larval  find  If,  densities see  of  I  the  and  the  w i l l  mortality  overloaded.  a b i l i t y  Predictions  3  longer  the  During  non-dispersers  distributions  overcrowding  and  some  behaviour  of  that  Although  Tyria  extinction  excess  adult  development.  refuges  and  produced  Eight  that  also are  some  dispersal  food  but  manner.  refuges.  complete  and  on  that  local  conditions  depend  food  of  dispersal  is  egg-clumping  period  able  belief  per  following  the  my  to  population in  was  vulnerable  density  acting  leave  experiment  unstable  density.  survival  w i l l  the  larval  overload  w i l l  of  the  out  10 on  m  x  a  experiments.  6  m,  and  closely-cut In  May  1972,  four lawn 160  244  single-stem these  plots,  randomly, another in  plants  the  large  the  sprayed larvae with in  from  young  Hence  the  density  plot  egg of  plant  food  was  could put  starting larvae,  then  i  out  a  the  25  was  a  2  plastic  The  and  and  The  that  had  that  t r i a l s  random  block with  m  2  top  been  were  in  run  uniform  the  rest.  with  replicates  5  stopped  was  design  two  per  wall.  distribution  plots, 2  0.33  and  plots.  preparation  Their  x  high  plots  was  small  cm  distributed  large  density  plots.  small  the  the  with  larvae.  two  larvae day  set For  with  the  the  at  on  The the  number  number  to  each  plot  of  larvae  from of  biomass  total  0  each  to  30.  t r i a l .  was  started  of  distributions  number  days  plant  was  total  proportional in  each  t r i a l  the  8).  twice  uniform was  a  and  (Fig.  ranging 12  placed  before  populations  over  of  t a l l i e d ,  plant  distributions spread  of  estimated  each  in  2  commercial  distribution ,  One  support.  on  a l l  were  into  plant  for  each  treatments.  were  was  m  Clearbrook  plants  Plant  erected  a  and  number  each  I  per  from  The  for  plots.  covered  Fluon,  experiment  follows.  larvae  was  each. used  3.33  f i f t h - i n s t a r  combination  as  each  crawling  x  The  small and  large  in  being  plots  with  two  the  inside  transplanted  plants  pattern  a l l  Around cm o n  20  one  for  were  the  the  of  of  plants larvae  biomass.  from  per  plant  Four  larval to  for  these  plant's  Fifty  on  fifth-instar  number  ranged  leaves  available  larvae  the  determined  The  175  to  in  random  counts  sixty  278  were  larvae  245  were  marked  from  different The  in  dispersal  considerably Prediction density  and  low  I  at  made  0.33  Survival  through  density  t r i a l s  and  defoliated.  random  plots larval  Prediction larval  similar with  In  was  would  f u l l  be  a  high  3.33 per  occurred  was  dispersal,  plants  per  plots  with  in  than  larval  expected lessen  with  total  m ,  but  2  high  in  low  plant  plots  with  distribution. to  the  remove  apply  plant  Larval  more  p o s s i b i l i t y  starvation  would  and  of  2  thus  low  rate  m .  higher  result  plots  with  distributions,  refuges  dispersal  larvae of  the  when a l l  to  the  comparisons  densities,  but  with  distributions.  3.  distribution  their  A  faced  at  uniform  dispersal  plants  between  much  distribution  and  being  2.  how  assumed  would  population  Prediction  see  plants  larval  density  were  to  mortality  uniform  plant  mortality in  more  1.  t r i a l  plants.  predictions  l i t t l e  high  each  food  random. increase  low  plant  survival In  those  the  reguirements  densities  would  be  plots  the  number before  of  but  higher  where  presence  larvae  pupation.  different  that  of  larval food  obtained  246  APPENDIX In  5. an  earlier  mentioned control  Tyria  that  agent  as  a  section  have  met  successful  establishment  cages,  and  instars, and the  as  the  feeding  of  i n i t i a l  not  the  following  land  with  sufficient  survival reduce  and the  reasonably mortality  during  infested  land  i n i t i a l rather of most  releases than  course  in the  favourable  (repeated)  areas  release  sites  of  of  are  there  too  few  stones  to  ensure  sparse  The  served  areas  like  Following  should  be  economically  early  the  third  and  before can  plants.  The Sites  well-drained both  a  pupal  cover  dense  to and  which  w i l l  minimize  owner  of  ragwort-  in those  economically  1  ground  predators; jacobaea  the  important.  sought:  S.  rearing  dispersal  be  better in  be  should  sites;  in  period  extremely  ground  more  some  chance  in  would  mortality  is  and  coincide.  in  release  dispersal.  that  habitat  greatest  on  made  I  biological offer  mortality  larvae  be  two  the  crowding  larval  were  increase  through  stand  might  I  losses  of  a  results.  is  major  pupation  abundance  System)  as  Larval  debris  adeguate  Tyria  l i t t l e  for  features  extensive  to  with  the  release  with  mixed  instars  period.  by  u t i l i z e  mortality  after  agent.  Tyria.  reared  f i e l d  i.e.  be ' m i n i m i z e d choice  be  of  control  Insect/Host-Plant  designed  preferred  fourth, major  can  to with  suggestions  larvae  (The  attempts  practical  As  biological  the  long  run  outlined  above,  important, establishment  i f  unless in  abundant  larvae  important  areas  the for where  247  Tyria  survival  reduce aid  the  is  height  dispersing  fauna.  of  Tyria  geographic  spread  of  study  probably  reach  high  density  is  to  not  some  acceptably and  probably  through  already  been made  evolutionary unaided.  then  too time,  easy  to  Yet  it  result  is a  vice  be  poor be  the  area  larvae  and  would  plants,  also  that  in  most  ragwort  for  the  w i l l  i f  the  defoliation  ragwort  at  a  a  point  low  Tansy to moth  cost  moth  effective  workers.  the  a r t i f i c i a l l y .  cinnabar  decrease  might  dispersers,  done  clear  to  predator  defoliate  accommodations versa,  an  arthropod  management,  agricultural  many  the  implement  The  tansy  pasture  and  in  level.  maintain,  by  and  in  releasing  best  that  densities,  low  to  to  would  suggests  good  made  prior  reducing  moth  high.  livestock  appear  are  necessarily  reduce,  probably  the  suggestions  This  w i l l  by  adults  l i t t l e .  ragwort  Grazing  grasses  larvae  As  These  lower.  density way  density that ragwort  Tyria to  do  to is has has over  the  job  


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