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Modification of microclimate by the blueberry leaf-tier, Cheimophila salicella (Hbn.) (Lepidoptera: Oecophoridae) Contant, Hélène 1988

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MODIFICATION OF MICROCLIMATE BY T H E B L U E B E R R Y LEAF-TIER, CHEIMOPHILA  SALICELLA  (HBN.) (LEPIDOPTERA: OECOPHORIDAE).  by HELENE CONTANT B.Sc, Universite Laval, 1982 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in THE FACULTY OF GRADUATE STUDD3S Department of Plant Science  We accept this thesis as conforming to the required standard  THE UNIVERSITY OF BRITISH COLUMBIA APRIL 1988 ° Helene Contant, 1988  In presenting this thesis in partial fulfilment of the requirements for an advanced degree at The University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.  Department of Plant Science The University of British Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: A P R I L  1988  ABSTRACT  The  ecology of Cheimophila  salicella  Hbn. (Lepidoptera: Oecophoridae), a  blueberry leaf-tier was studied on high-bush blueberry, Vaccinium in  Richmond, British  lichen Xanthoria The  Columbia. The females  frequently  laid  corymbosum  their  L.,  eggs in the  sp., an oviposition site not previously reported for this species.  possible microclimatic  advantages  of such behaviour are discussed. In the  Field, females required longer than males to complete their 6th instar, so females were usually bigger than males in that instar.  The the  leaf shelter made by the larvae modified their microenvironment in  field. On clear and sunny  6-7°C above than  those of ambient  the air as long  days, measurements of shelter temperature were air. The shelter  as the incoming  temperature  radiation  radiation levels dropped, the shelter temperature fell temperature. On  levels  remained  were  high.  warmer A s the  to, or a little below, air  cloudy days, there was no significant difference  between the  daily maximum shelter and air temperatures.  Under  clear  skies, the daily  amplitude of temperature  greater inside the shelter than outside. A of  such fluctuations on development  fluctuations  was  laboratory investigation of the effects  showed that a large amplitude increased the  developmental rate of the lst-4th instars. This increase in rate of development was  probably due to an accumulation of extra  thermal units  (Yeargan 1980)  occurring in the large-amplitude regime. However, the high temperature of this regime retarded pupation, and the later instars required longer to complete their  ii  development. the  same  amount  "medium its  Overall,  in  the  small  of time to develop f r o m  amplitude",  thermophase  larvae  was  the field. F i f t h - and  slowed  larval  longer  than  and  large  that w h i c h  probably  the  insect  took longer  The than  if  microclimate of the shelter provides  they  development. would autumn  not  pupae; females were, on average,  were Without  be  able  subjected the to  to  extra  complete  ambient  degree-days its  larval  frost.  iii  air  because  t h a n males  12.7  mg  the larvae and  provided  larger  by  development  of  encountered  in  to complete their amplitude than  w i t h more  the  the  regime males.  degree-days  promotes  shelter,  before  regime,  length  heavier  therefore  required  third the  normally  development, both i n the laboratory and i n the field. The produced heavier  regimes  hatching to pupation. A  development,  sixth-instar females  amplitude  C. first  faster salicella lethal  TABLE OF CONTENTS ABSTRACT  ii  Table of Contents  iv  List of Tables  vi  List of Figures  vii  ACKNOWLEDGMENTS  ix  I. INTRODUCTION  1  II. CHEIMOPHILA SAUCELLA: DESCRIPTION AND LIFE HISTORY A. DESCRIPTION OF THE INSECT B. LIFE HISTORY  3 4 7  III. BIOLOGICAL NOTES A. METHODS B. RESULTS 1. Notes on the life history and ecology of C. salicella 2. Larval density in the field 3. Proportion of males and females 4. Density of individual instars C. DISCUSSION 1. Life history and ecology of C. salicella 2. Larval density in the field 3. Proportion of males and females 4. Length of development of individual instars in the field  10 10 14 14 21 24 27 30 30 32 32 34  IV. INSECT THERMOREGULATION A. LITERATURE REVIEW 1. Regulation of metabolic heat 2. Heat exchange with the environment 3. Microclimate B. MATERIALS AND METHODS C. RESULTS 1. Clear conditions a. Solar radiation b. Shelter and air temperatures c. Differences between shelter and air temperatures 2. Cloudy conditions a. Solar radiation b. Shelter and air temperatures c. Differences between shelter and air temperatures 3. Other results  35 35 36 37 42 50 53 55 55 55 63 69 69 69 72 72  iv  D. DISCUSSION  75  V. EFFECTS OF THERMOPERIOD ON INSECT DEVELOPMENT A. INTRODUCTION B. MATERIALS AND METHODS C. RESULTS 1. Mortality 2. Developmental time a. Early instars b. Middle instars c. Late instars d. 1st- to end of 6th-instar 3. Pupal weight D. DISCUSSION 1. Mortality 2. Effect of temperature regimes on larval development 3. Importance of the shelter on larval development  83 83 88 94 94 94 94 97 97 98 99 99 99 102 106  VI. CONCLUSION  108  LITERATURE CITED  Ill  APPENDIX I  118  APPENDIX II  119  APPENDIX III  120  APPENDIX IV  121  APPENDIX V  122  APPENDIX VI  123  APPENDIX VII  124  APPENDIX VIII  125  v  LIST OF TABLES TABLE 1. Weather during the days when microclimatic measurements were taken in a high-bush blueberry field in Richmond, B.C. in 1985  54  TABLE 2. Mortality for each laval period of Cheimophila salicella larvae reared at daily average temperatures of 12° and 16°C  95  TABLE 3. Time required by Cheimophila salicella larvae to complete each larval period in 3 temperature regimes having a daily average temperature of 16°C  96  TABLE 4. Weights of 14 day-old Cheimophila salicella pupae from larvae reared in three temperature regimes having a daily average temperature of 16 °C  100  vi  LIST OF FIGURES F I G U R E 1. Cheimophila salicella female (a) and male (b) resting on a branch of high-bush blueberry in Richmond, B.C. Note the atrophied wings of the female and her extruded ovipositor  5  F I G U R E 2. Two typical leaf-shelters made by the larvae of Cheimophila salicella on high-bush blueberry plants in Richmond B.C. The first one (a) consists of 2 green leaves tied together, and the second (b) is made of one leaf severed at the petiole and tied to a green leaf.  12  F I G U R E 3. Xanthoria sp., a lichen abundant on high-bush blueberry in Richmond, B.C. is hiding a small egg mass of Cheimophila salicella. The eggs are dark pink, indicating that the embryonic development is well underway  15  F I G U R E 4. Frequencies of different categories of shelter made by the larvae of Cheimophila salicella throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C  19  F I G U R E 5. Changes in Cheimophila salicella larval density per leaf throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C  22  F I G U R E 6. Proportions of Cheimophila salicella male and female larvae throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C  25  F I G U R E 7. Densities of Cheimophila salicella larvae in each instar throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C  28  F I G U R E 8. Average radiation levels (a), air and shelter temperatures (b), and T (c) measured on August 3, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.)  56  F I G U R E 9. Average radiation levels (a), air and shelter temperatures (b), and T (c) measured on August 14, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.)  58  F I G U R E 10. Average radiation levels (a), air and shelter temperatures (b), and T (c) measured on August 17, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.)  60  e x c e s s  e x c e s s  e x c e s s  vii  F I G U R E 11. Radiation levels (a), and T (b) measured for a northeast-facing shelter made of one green and one red leaf in a high-bush blueberry field i n Richmond, B.C. on August 17, 1985  65  F I G U R E 12. Radiation levels (a), and T (b) measured for a south-facing shelter made of one green and one red leaf i n a high-bush blueberry field i n Richmond, B.C. on August 17, 1985  67  F I G U R E 13. Average radiation levels (a), air and shelter temperatures (b), and T (c) measured on August 7, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.)  70  F I G U R E 14. Average radiation levels (a), air and shelter temperatures (b), and T (c) measured on July 29, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.)  73  F I G U R E 15. Average minimum and maximum temperatures between April and October at the Richmond Nature Park station of Environment Canada calculated over a 9-year period (1977-1985). The station was located < 1 km from the study site. (Bars represent SD.)  89  e x c e s s  e x c e s s  e x c e s s  e x c e s s  viii  ACKNOWLEDGMENTS  It Dr.  has  W.G.  source  a  of inspiration. I  V.C.  of  this  B.D.  for  philosophy  also  thank  me  to  work  under  the  guidance  of  of science and broad knowledge have been him  for  his  continual m o r a l support  a  and  for  helpful suggestions  throughout  all  his  encouragement.  extras that he considered being " a l l p a r t of the service".  Dr. stages  priviledge  Wellington. H i s  the m a n y  Dr.  been  Runeckles  Frazer  has  thesis.  I  always  had  provided m a n y  am  grateful  time for  for  interest  discussion  and  his  and  approach  to ecological  research helped me develop a new perspective towards both ecology and research. I  thank  Dr.  encouragement  D.H.  J.  Raine  developing Mr. Dr.  P.  Virgino  identification  her  insights am  of for  me  find  this  a  study  study.  allowing  site  My  me  to  offered  go  statistics. Dr.  of  (Hbn.),  Cheimophila  salicella  M.  Kelly,  and  F i n a l l y , I w a n t to thank L. at a l l stages  Kingma  to  their  patiently helped w i t h the  V.  help  and  use  sp. and Parmelia  J.  this  grateful to P.  thanks  L u t z o n i identified Xanthoria Erho,  into  work,  for  T h e r r i e n for  her many  and for helping w i t h some of the microclimatic measurements.  helped  stage  J . Hall  for  and for editing the thesis. I  valuable discussions Mr.  Henderson  and  several Mr.  W.B.  invaluable  his  of this work, his  am  grateful for the f i n a n c i a l help provided b y  FCAC.  ix  understanding a Post  the  Barone  and field.  confirmed the  Schofield Cheng, technical  F.  and  F.  Contant, assistance.  W i l l m s for her generous hospitality and D.J.  for  in  blueberry  J.-F. Landry  sulcata T a y l . R.  provided  F.  high-bush  Dr.  ideas  Quiring  and encouragement.  Graduate  Scholarship  I  from  I.  Temperature development  of  INTRODUCTION  is one of the more important factors regulating growth and insects  (Andrewartha  and  Birch  1954; Chapman  1982;  Wigglesworth 1972). Each species has its own range of temperatures i n which i t can  survive  and develop. Within that  temperature  range, development  usually  proceeds faster at the higher levels.  Many insects have adaptations that allow them to survive and develop at temperatures outside their preferential range; e.g., at levels that may, for a time at least, accelerate their development.  Faster development  can benefit insects by  reducing the length of time that they are vulnerable to parasitism, for example, or by allowing them to go into diapause before the onset of adverse conditions. Such  adaptations  supercooling),  can  be  or physical  behavioural  (e.g., a hairy  (e.g., body).  basking), Shelters  physiological  made by some  (e.g., leaf  miners, leaf rollers, tent makers, and bag makers can increase the temperatures and/or humidities present in these insects' immediate 1983, Henson  1958a, Henson  surroundings (Barbosa et al.  1958b, Henson and Shepherd  1952, Sullivan and  Wellington 1953).  Cheimophila caterpillar  commonly  constructs  shelters  salicella found which  (Hbn.)  (Lepidoptera:  on high-bush probably  Oecophoridae),  blueberry, Vaccinium  modify  surrounding  a  leaf-tying  corymbosum L.,  temperatures.  This  microlepidopteran makes a shelter by tying or rolling together one or more leaves of a shoot. It has a long larval  stage, lasting from  1  M a y to October. Without  2 the  occasional  increases  in  temperature  that this insect could not pupate  created by  the  shelters,  early enough i n the a u t u m n  it is  conceivable  to escape  the  first  lethal frost.  Although Columbia first  C. salicella is considered  (Raine  part  1966),  of this  observations  very  thesis  little  outlines  on its ecology  is  a pest on high-bush blueberry i n  known  the  insect's  (chapter III).  One  the effects of the shelter on temperatures temperature measurements day  and  shelter of  under  on  large  C. salicella  various  microclimate fluctuations larvae.  inside  climatic (chapter of  IV).  on  ecology.  history  Accordingly,  (chapter  a i m of this thesis  II)  was  and  the some  to determine  C. salicella larvae. F i e l d  the shelter at different times of the  were  Chapter  temperature  life  its  experienced by  and outside conditions  about  British  used to V  the  deals  assess with  development  the effect of the  the  potential effects  and  survival  of  II. CHEIMOPHILA  Cheimophila species  found  from  SALICELLA:  salicella England  (Hodges 1974). In North  DESCRIPTION AND LIFE HISTORY  (Hbn.) to  (Lepidoptera:  Siberia  Oecophoridae)  (Meyrick  is a palearctic  1927) as well as i n Japan  America, it was reported for the first time i n 1955 by  Andison (Raine  1966) in the Lower Fraser Valley of B.C. B y 1962, the insect  was  a nuisance  considered  pest  in commercial  fields  of high-bush blueberries,  Vaccinium corymbosum L. Wherever the crop is hand-picked, larvae feeding among the  berries can be picked  along  with  them. Where  machine picking is used,  larvae feeding on the leaves as well as those on the berries are dislodged into the picking crates. In both instances, additional sorting is required.  Although  the insect's main host  plant is the high-bush blueberry, it is  also commonly found on Salix sp. (Salicaceae) and Spirea sp. (Rosaceae) and may occur  on Betula sp. (Betulaceae), Alnus  Prunus Cornus  sp. (Rosaceae),  Myrica  sp. (Betulaceae), Acer sp. (Aceraceae),  sp. (Myricaceae),  Berberis  sp. (Cornaceae), Potentilla sp. (Rosaceae), Ledum  sp. (Berberidaceae),  sp. (Ericaceae),  Kalmia  sp. (Ericaceae), Vaccinium sp. (Ericaceae), and Rubus sp. (Rosaceae) (Raine 1966; Gillespie  1981), all of which  commercial  blueberries  may  are planted.  grow  i n the acidic  It has also  (Rosaceae) i n Holland (Reichert 1932).  3  been  peat recorded  bogs  i n which  on Rosa sp.  4 A.  D E S C R I P T I O N  The  O F  T H E  adult female  found in North America (Fig.  I N S E C T  (8-13 mm  long) is the only brachypterous  north of Mexico  oecophorid  (Raine 1966, Hodges 1974). The body  la) is grey speckled with white. The atrophied fore wing is light grey and a  horizontal dark band divides the wing also found  approximately in half. A dark section is  at the apex of the wing.  The fore wing  is 3-5 mm  long (Hodges  1974). The ovipositor, visible when extruded, is orange. The legs have alternating white and black bands. This camouflage  The with  conceals moths resting on old bark.  adult male has fully developed wings (Fig. lb) and is 10-12 mm  the wings  varies from  folded  (Raine  1966).  long  The colour and pattern of the forewing  one individual to another. Most are light brown with 2 transverse  brown bands separating the wing in 3 sections. On the side of the band closest to the body, there is a very light patch, varying in colour from white to beige. In  some individuals this patch is very small, whereas in others it is larger and  resembles  a  triangle  with  its base  resting  on the dark  brown  hindwing is brown and lacks a distinct pattern. A detailed taxonomic  band. The description  of the insect is given by Hodges (1974).  The  eggs  are smooth, oval  and about  0.75 mm  long  (Raine  1966).  Opaque, white, and sticky when first laid, the eggs later become reddish (Raine 1966).  The  larvae are about 1.2 mm  long when they hatch and about 24  mm  5  FIGURE 1. Cheimophila salicella female (a) and male (b) resting on a branch of high-bush blueberry in Richmond, B.C. Note the atrophied wings of the female and her extruded ovipositor.  7 long  when  mature  (Raine  1966).  There  are  6  instars.  The  abdomen  is  whitish-green. Following a moult, the head capsule is smooth and yellowish, but becomes dark brown as the cuticle hardens. The prothoracic shield is dark brown and the legs are black. The  metathoracic legs are lobate and enlarged, and they  fibrillate when the larva is disturbed (Reichert 1932).  The  pupa is obtect and yellow when first formed. Later, it becomes light  brown with darker wing pads. The pupa of the male is generally smaller in size (both in length and  in width) than that of the female. Raine (1966) reported  average lengths of 10 mm and  for the male and  13 mm  for the female. The  female pupae can also be differentiated by the ratio of wing-pad  pupal length, as the wing-pads pupal  length,  whereas  of the males  those of the  female  male  length to  extend at least two-thirds of the extend  less  than  one-half (Raine  1966).  B. LIFE HISTORY  In  the  field,  adults' emerge  from  the  ground  between  mid-March  and  mid-April. Males emerge a few days before females in a ratio of 1 male to 2 females (Raine 1966). Emergent females climb up the stems of blueberry bushes and begin "calling" with their abdomen and ovipositor extruded. A pheromone has been isolated and identified by Gillespie et al.  female-produced  (1984). Mating  may  last between 20 min. and l h and males mate with more than one female (Raine 1966).  8 Unmated rarely  females may  oviposit before they  lay eggs, but i f males are present  mate. Mated  the females  females lay an average of 440 eggs,  whereas unmated ones lay an average of 382 (Raine 1966). The eggs are placed under  loose bark,  leaves (Raine  under  the scales of flower buds and in the axils  of new  1965, 1966). According to Raine (1966), the most favoured  site for  oviposition is under the shreds of loose bark at the base of the bush.  In  the field, eggs may  incubate  for 8 weeks and all the viable ones  hatch during a 2-week period starting in the middle of May (Raine 1965, 1966). The  larvae emerge in numbers on the first  warm  day after  the eggs  have  matured (Raine 1966).  Larvae and  emerging from eggs laid under flower bud scales enter the flowers  eventually feed  prematurely  on the fruit  as it develops.  Infested berries often ripen  and have dead flower parts clinging to them  (Raine  1966).  Larvae  emerging from eggs laid in the axils of leaf buds enter the bud and feed on the innermost  leaf, usually cutting it at the base so that ultimately i t dries and  turns black. Larvae  emerging from eggs laid under the loose bark walk upwards  to the leaf and flower buds.  When  the leaf buds have opened, the larvae that were feeding among  them either fold over the edge of one leaf or tie 2 leaves together. Either way, the  larvae  severed  produce  shelters for themselves.  One  of the two leaves  is often  at the petiole and soon turns red. Later, as the leaf dries, i t turns  brown. Such leaves are very  conspicuous  in the summer when all other leaves  9 are  still  green. Larvae  may  feed on  their  own  shelter  or browse  outside it  (Raine 1966).  Pupation occurs in October. Most larvae pupate  within the leaf shelters,  which later fall to the ground. Occasionally they remain attached to the branches (Raine  1966). Larvae  have  also been  reported to pupate  in the litter  (Raine  1966).  Parasites of the larval, pupal and  adult stages of C. salicella have been  recorded. Gillespie (1981) found one Apanteles sp. (Braconidae) and one Glypta sp. (Ichneumonidae) iridescens parasitized  parasitizing  French by  a  the larvae. Raine  (Braconidae) parasitized secondary  parasite,  parasites of the pupal stage, Compsilura adult 1966).  stage, Tomosvaryella  sp.  the  (1966) reported that larval  Habrocytus  stage  sp.  and  Macrocentrus  in turn  was  (Pteromalidae). Dipterous  concinnata (Mg.) (Tachinidae) and of the  (Pipunculidae) have  also  been  recorded  (Raine  III.  Cheimophila  salicella  BIOLOGICAL NOTES  has  been studied very  only investigators, Raine (1965, 1966)  and  little in North  Gillespie  (1981, 1984), were  concerned with the economic impact of the insect on B.C. life  Their  studies therefore concentrated  cycle, assessing  the  relative  on  insect, and  determining  the  the blueberry  The  mainly  industry in  obtaining basic information on  abundance of the  damage, identifying parasites of C. salicella  America.  and  larvae  and  the  the  amount of  their potential for controlling the  effectiveness of various insecticides and  the  proper  timing of their application, i f required.  This chapter presents some new  information on the behaviour  of C. salicella, including observations on the types of shelter made by throughout its larval stage. Since there was the various instars of C. was  no  information on  and  ecology  the insect  the duration of  salicella in the literature, this aspect of its life cycle  also recorded in conjunction with data on larval density and  sex ratio.  A. METHODS  The B. C.  The  garden, on  work was 1.8  hectare  done in a high-bush blueberry field  the east by  a  was  cranberry  young blueberry bushes about 1.2 field. The owner  did  bounded on  m  field,  the on  tall, and  the  field  north south  located in Richmond,  by  a by  on the west by  house and a  small  small patch  another high-bush  blueberry bushes had been planted at least 10 years ago, but the not  know  the  exact  planting  10  date.  The  field  of  contained  new  several  11 blueberry  cultivars. Spraying  used in this field. Pruning  Data  on  larval  for mummy berry was was  18  and  insecticide was  done in the spring.  development, density,  collected between June  done, but no  and  October 28,  preferred  1984.  shelter  types  Every bush in the field  given a number so that those to be  sampled could be  a  picking season, however, bushes that  random number table. During the  already  been  picked  completed, and  were  each week  (excluding  cardinal quadrants was  a  few  the  2  weeks, harvesting  chosen and  with  and  could  not  be  accurately  was  average of  6.5  weeks when  there  was  no  branch  on  all the  leaves  on  salicella  without larvae were recorded  larva, the instar, type of shelter and  had  resumed. An  its ramifications were examined for the presence of C.  total numbers of leaves  age  After  was  selected each week from  Bushes were not re-sampled. From each bush sampled, one  each of the and  sampled.  random sampling of all bushes was  bushes were sampled sampling).  not  were  this branch larvae.  and,  The  for each  sex, when known, were noted. When larval  determined,  such  individuals were  recorded  as  "unknown instar". Similarly, when their sex could not be distinguished, individuals were classified, "unknown sex". Shelters were divided into the following categories: 1) green shelter: consisted of 2 green leaves tied together (Fig. 2a); 2) semi-dried (Fig.  shelter: consisted of 1 green and  1 dead leaf tied  together  2b), or 1 partially dried leaf folded or rolled on itself;  3) dried shelter: consisted of 2 dead leaves tied together or of 1 dried leaf folded or rolled on itself; 4) "other" shelter: any  shelter which did not fit the previous categories.  12  FIGURE 2. Two typical leaf-shelters made by the larvae of Cheimophila salicella on high-bush blueberry plants in Richmond B.C. The first one (a) consists of 2 green leaves tied together, and the second (b) is made of one leaf severed at the petiole and tied to a green leaf.  14 B.  1.  RESULTS  Notes on the life history and ecology of C.  Two  species of lichen, Xanthoria  abundant on the blueberry bushes. Xanthoria the bushes, whereas P. sulcata of C. salicella  salicella  sp. and Parmelia  sulcata  Tayl. were  sp. occurred in the upper section of  was located mainly in the lower section. Females  frequently oviposited in Xanthoria  sp. (Fig. 3) but never laid their  eggs on the other kind. Some eggs were laid between the lichen and the branch surface, and were well hidden However, when a large mass of eggs was laid in the lichen, some were deposited on the upper surface of the lichen and could be seen more easily, especially as they developed to the stage when they turned pink. (Infertile eggs remain white and do not hatch.)  Most eggs were located under loose bark, but contrary to Raine's findings (1966), they were not at the base of the canes. The loose bark at the base was usually grey, thin and easily peeled. The loose bark which the 1984-1985 generations seemed to prefer was located mainly in the top half of the bushes, where the branches were reddish-brown. This bark was thicker than the bark at the bottom of the canes, and not so easily peeled.  Raine (1966) mentioned that larvae foraged outside their shelters. I have also seen evidence of this. Leaves  close to C. salicella  leaf shelters showed  increasing damage from one day to the next. Rarely, however, have I seen a larva eating leaves outside the shelter during the day. The only larvae I have  15  FIGURE 3 . Xanthoria sp., a lichen abundant on high-bush blueberry in Richmond, B.C. is hiding a small egg mass of Cheimophila salicella. The eggs are dark pink, indicating that the embryonic development is well underway.  16  17 seen outside shelters during the day resting on  a twig or leaf. The  were feeding on  the berries or occasionally  amount of damaged leaves suggested that many  larvae must feed outside their shelters. I checked for possible nocturnal feeding at 2300h  (standard  time) and  at  OlOOh, but  in those  periods, at least,  the  majority of the larvae were in their shelters.  C.  salicella  However,  as  constructions  larvae  the  initially  leaves  appear.  open  Apart  occupy and  from  flower  expand,  the  or a  categories  leaf  buds  greater listed  (Raine  variety  1966).  of  larval  previously, the  larvae  sometimes loosely tie a leaf, dead or alive, to dried flowers or fruit. A  leaf  may  also  are  tied  be  tied  together  to  by  a  small  branch. Occasionally, more  1 larva. I have  also seen  2  than  2  leaves  different shelters having  1  leaf in  common.  The  larva uses silk to tie leaves together. It does so by moving back  forth from  one  other, and  lining the developing  whenever  the  leaf to the  larva  enters  other, each time pulling the  or  tunnel inside the shelter, and the  tunnel remain  Larvae  not  only  both the green and dry  leaf showed  its shelter. Eventually, there  cover  is a  this is where the insect usually rests. The entrance  and  exit holes  occupant.  shelter, eating  leaves. Frequently, shelters made of 1 live and  offered by  larva tied a new  one  on  the  leaf was  leaf over the  dry  than on  the  live  much reduced by  small one.  silk  ends of  for the  also consumed their own  more evidence of feeding  Sometimes, when the activity, the  leaves  outside, they  the dry  closer to each  shelter with a layer of silk. Silk is also added  open, serving as foraged  leaves  and  1 one.  feeding  However, larvae often  18 seemed cover leaf  to tolerate shelters the insect. I  scarcely  were  not  layer  where  tape"  and  long  found  as  >1  noise m  The  diet. In  shade.  contain  produced  by  the  testified,  appear  blue-grey  took  a  the  on  leaves when  pink  they  colour  insect  did  had  as  not  behaviour  eaten  but  a  some  feeding  feed or  move  the body  These  dried leafrolls  rather  in  the  inside  "flagging  of it. Raindrops leaves  and  absorbed  permeable.  of  the  metathoracic  occurred at night as  abdomen.  reached  dried  legs  could  w e l l as  be  i n the  v a r i e d according to their size and their  green  were  rolled,  shelter of blue  of e a r l y - i n s t a r larvae were  they  compacted together, reducing  larva.  of one  differently. The brown  fibrillation  a  j u s t big enough to  made  l a r v a made  colour of the larvae  the field, the abdomen  the  was  of the bush,  One  the tape  shelters  the green ones were less  abdominal  feeding  stage,  in  to  periphery  f r o m the l a r v a . T h i s  larvae  skin  the  2 leaves  seen  dew affected live and dead leaves  The  day.  enough  more  holes  the water, whereas  heard  on  1 of the  frequently  wide  there w a s  had,  also  and  usually  morning  have  in which  on  Their  berries.  translucent  Later,  their pre-pupal very  much.  length. The  yellow, whereas  in  stage.  The  the  In  thorax  the and  older  skin  could  fall,  their  pre-pupal the  head  legs were no longer functional  and the body turned whitish-yellow.  Comparisons summer  and  fall  at  the  number  of  abundant total green  shelters  of  the  types  4)  showed  that  beginning  of the  sampling  (Fig.  shelters  were  more  in  June  abundant  of  larval  and  shelters  the  green  and  period, each  July.  (55%)  that  After  than  the  any  appeared  semi-dried  shelters  comprising week  other  of  type  during  35%  August of  the were  of the 6,  the  shelter,  but  19  F I G U R E 4. Frequencies of different categories of shelter made by the larvae of Cheimophila salicella throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C.  JULY 1984  AUGUST  D A T E  SEPTEMBER  OCTOBER  to o  decreased rapidly after the week of September shelters declined steadily from The  10. The frequency of semi-dried  the beginning to the end of the sampling period.  dried shelters were never very abundant, except during the week of October  8, when  they  represented  about  3 0 % of all shelters.  "Other"  shelters  were  relatively abundant (30%) at the beginning of the sampling period, but were very scarce  during  July,  August  and  September.  Thereafter, they  became  most  abundant as the number of green shelters decreased. In fact, during October the "other" shelters represented between 45-65% of the total shelters present.  2. L a r v a l  density i n the  field  With the exception of a 2-week period between Aug. 13 and Aug. 27, the density of C. salicella larvae on the bushes (Fig. 5) decreased gradually from the beginning of sampling on June 18 to its end on Oct. 28. The initial density on June  18 was  =0.10  larva/leaf. By  the week  of July  density had decreased to 0.07 larva/leaf, and remained the following  5 weeks. A  subsequent  2, the average  larval  relatively constant during  increase in density  occurred during the  week of Aug. 13, and densities of 0.15 larva/leaf were found until the end of the following week. This increase was quickly followed by a pronounced in population, and by the week of Sept.  10 the density  decrease  was less than  0.04  larva/leaf. Few insects were found between the weeks of Sept. 24 and Oct. 10, when densities ranged from 0.01 to 0.02 larva/leaf.  22  F I G U R E 5. Changes in Cheimophila salicella larval density per leaf throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C.  0.125-1  0.000  1  13  1  26  JUNE 1984  1  2  1  9  1  16  1  23  JULY  1  SO  1  6  1  13  T  20  1  27  AUGUST  1  3  1  10  1  17  1  24  SEPTEMBER  1  1  1  8  1 r—  16  22  OCTOBER to  DATE  24  3. Proportion of males and females  Pre-gonads were not apparent in half-grown and  i t was not until  July  2 that  larvae early in the summer,  the sex of some  identified. The proportion of males (Fig. 6) fluctuated  older larvae  could be  around 0.45 for most of  the summer until the week of Sept. 17. A sharp decrease in the week of Sept. 24 brought the proportion of males down to 0 by the week of Oct. 8, followed by  an increase to 0.20 in the week of Oct. 15, before  the ultimate decrease  during the last week of sampling.  The  proportion of females (Fig. 6) remained between 0.20 and 0.30 up to  the week of Aug. 13, when it rose to 0.40. A steep increase in the proportion of females corresponding  to the decrease in males occurred  during the week of  Sept. 24, and the proportion of females remained high for 4 weeks, attaining a peak value of 0.88 during the week of Oct. 1.  Summations of the proportions of individuals of the 2 sexes do not equal 1.00 because of the presence of larvae of unknown sex. The proportion of larvae of unknown sex was relatively high  (about 0.25) from the week of July  2 to  the week of Aug. 13. A decrease in the proportion of these individuals followed, and  i t remained less than 0.10 between the weeks of Aug. 27 and Oct. 1. A t  the  end of the sampling  period, during the week of Oct. 22,  rose to a very high value of 0.67.  their  proportion  25  F I G U R E 6. Proportions of Cheimophila salicella male and female l a r v a e throughout the 1984 s u m m e r i n a high-bush blueberry field i n Richmond,  B.C.  I.O-i  » J  U  L  Y  • '  20  27  AUGUST  DATE  3  10  17  24  SEPTEMBER  1  8  16  22  OCTOBER  to  27  4. Density of individual instars  At 2nd 2  the time sampling began (June 18), the larvae were already  i n their  and 3rd instar (Fig. 7). A l l larvae had completed their 2nd instar by July (no sampling  was done in the week  of June  25). The 3rd instar was  completed during the week of July 9. The density of 4th instar larvae rose from 0 to 0.059 larva/leaf between the weeks of June 18 and July 2. It peaked at 0.064 larva/leaf during larvae  decreased  5th-instar larvae near longer  the week of July  9 and, as the density  to 0.010 larva/leaf i n the week increased  of July  23, the density of  to 0.056 larva/leaf and reached  0.07 on the following week. The 5th-instar density  of 4th-instar  a maximum  remained  high  value for a  period of time than did that of the 4th-instar (about 4 weeks compared  to 2 weeks for the 4th instar). The density of 6th-instar larvae increased  slowly  at first, then more rapidly i n the week of August 13. It reached a maximum on  August 20, when  the density  of 5th-instar larvae was still relatively  high,  decreased between the weeks of August 27 and September 10, increased again i n the week of September 15 and slowly decreased until the week of October 22.  A  size discrepancy  between the sexes of both 5th- and 6th-instar larvae  made i t difficult to differentiate the two age groups. The density unknown instar remained very point, i t increased  with  of larvae of  close to 0 up to the week of Aug. 6. A t that  the density  of the 6th-instar larvae  and reached  a  maximum value of 0.031 on the week of Aug. 27. In that week, the density of larvae  of unknown  individuals.  instar  The density  was greater  of larvae  than  that  of unknown  of recognizable instar  gradually  6th-instar decreased  28  F I G U R E 7. Densities of Cheimophila salicella larvae in each instar throughout the 1984 summer in a high-bush blueberry field in Richmond, B.C.  D E N S I T Y  O F  L A R V A E  / L E A F  30 thereafter to a low value during and after the week of Sept. 24. Larvae  took  longer to complete their 5th and 6th instar than to complete their 4th instar.  The  first  pre-pupae were seen during the week of Sept.  10 and i n the  week of Oct. 8 the first pupae were recorded on the bushes.  C. DISCUSSION  1. L i f e  history  Species  and  ecology  survive  by  of  C.  salicella  spreading  the risks  of mortality  through  their  populations (Wellington 1977). One way to achieve this goal is to use different oviposition sites. The females of C. salicella first  consists  advantage appreciably  of open  of being  areas,  such  well exposed  seem to use 2 kinds of sites. The  as flower buds. There to radiant heating  increasing the rate of embryonic  the eggs have the  during  the day, thereby  development. During  a calm and  sunny spring this advantage might outweigh the dangers of greater exposure to parasites and predators. During  a windy spring, convective cooling would reduce  the advantage of radiant heating in these exposed places.  The  second kind of oviposition site is more protected. It includes patches  of lichen and loose pieces of bark. Both rain and thus and  loose bark  shield  with  sites minimize  reduce heat loss due to convection absorb moisture  a relatively  high  from level  exposure to wind and  and evaporation. Both lichen  the air and may provide of moisture  for longer  the eggs  periods  they  than the  exposed solar  eggs would  experience.  radiation (Lewis  ambient  temperatures  1962;  Since  bark  Kershaw  and  lichen also can  1985), they  for incubation. Protected  sites  be  also  provide  have  some  heated higher  by than  disadvantages,  however. Larvae hatching from eggs laid in loose bark or lichens have to travel farther to their first feeding sites than larvae from eggs laid on leaf and  flower  buds, the  which  initial  source  of  food.  Small  larvae  often  fall  from  twigs,  increases the risk they face after hatching. Nevertheless, the females prefer these protected oviposition sites and  Larvae  from  disperse than those females walk up  use them when they are available.  eggs laid  in protected  from eggs laid on  sites  are  probably  the food source.  As  more  prone to  the newly emerged  the stems, they first encounter the protected sites and  they continue their ascent toward the end  later, as  of the branches, reach the flower  and  leaf buds. It is therefore possible that most of the eggs first produced by  the  females are laid in the protected sites. The  are  also  those  that  have  development. Wellington received pluviale  by  the  eggs  received  the  greatest  (1959, 1965) of the  first  has  western  eggs laid by  amount  the females  of nutrients during  shown that the  amount of nutrients  tent caterpillar, Malacosoma  (Dyar), determines individual behaviour  their  californicum  which in turn can affect survival.  This is an aspect of the ecology of C. salicella that could be studied further.  dried  Green and  semi-dried shelters seemed to be preferred by most larvae over  ones, but  the  mid-August and  reason  for  the  greater  abundance  of  green  shelters in  early September is not clear. In contrast, the relative abundance  of "other" shelters in mid-June was  due  to the presence of dried flowers at that  32 time. The next increase i n "other" shelters at the end of September was almost entirely due to the high proportion of shelters made of yellow or red leaves.  2. Larval density in the field  As  sampling  was not started until mid-June, I missed the first peak in  larval density. A high mortality was probably  sustained by early instar larvae as  they often have to walk toward their food source The  or disperse to other branches.  slow decrease in population between June 18 and Aug. 6 reflected a steady  mortality during that period. The peak i n density encountered during the weeks of Aug. 13 and Aug. 20 was unexpected, however. Hand picking of the berries had  started before then and by Aug. 9 one half of the field had already been  picked. Since disruption from picking can disturb the population of C. salicella on a bush, it seemed preferable to sample bushes only in the "unpicked"  half of  the field. Perhaps cultivars more susceptible to C. salicella were sampled i n this section of the field and caused the higher densities recorded  during the weeks of  Aug.  13 and Aug. 20. After the week of Aug. 20, when all the bushes had  been  picked,  obtained  after  the whole  field  was sampled  the end of August  as before.  reflected  The low density  level  natural mortality (and eventually  pupation), but also mortality caused by picking.  3. Proportion of males and females  Males and females were easier to differentiate when the larvae were well grown, as evidenced  by the high  proportion of larvae of unknown sex during  33 earlier sampling. Since the proportion of each sex probably  during the early instars  was  close to that in the later instars, it can be assumed that many of the  "unknown" larvae were, in fact, female. That assumption brings the proportion of males and  A  females in the early stages  major change occurred  of females increased This  change was  to  after the week of Sept. 17, when the proportion  dramatically, while  due  to the  =50%.  that of males decreased nearly to  shorter developmental period of the  0%.  males. After  most of the males had pupated, the females still required at least 3 more weeks to complete their larval development. The of males shown in Fig. 6 was larvae left in the  The  artifact caused by  increase in larvae of unknown sex  whose sex  in the proportion  the very  small number of  field.  sampling period represented field  an  last increase to 2 0 %  at the end  of the  the high proportion of pre-pupae then present  in the  could not be  that occurred  determined because their opaque colours (pink or  yellow) masked the pre-gonads.  Male and despite  the  1966). A factors  fact that adults occur in a  more detailed study  affecting late-instar  observations selection  female larvae were present in these samples in a 1 to 1 ratio  of  early-maturing  showed  a  high  potential hosts males.  ratio of 1 male to 2  than mine should  larvae  as  well as  the  parasites  (Raine  include assessments of mortality pupal  mortality. My  rate of pupal parasitism, so by  females  that  there  preliminary  may  discriminates  be  against  some the  34  4. Length of development of individual instars in the field  The  progression  of instars i n the field was mainly  predictable. However,  the density of 6th-instar larvae was lower than expected. The higher number of "unknown" included  instars  a large  during  the weeks  proportion  of Aug. 27 and Sept.  of 6th-instar larvae  which  would  10 could  have  account for  the  lower than expected densities during these weeks. In fact, adding the totals of these unknown instars to that of those for the 6th instar (Fig. 7) provided a more realistic pattern for the latter during the period from Aug.  27 to Sept. 15.  The  second peak i n the density of both 5th- and 6th-instar larvae seems due to  the  lack of synchrony  between  male  and female  development that was noted  earlier. The more prolonged development of females also explains weight. In future work, accurate- determination would  require  width,  which  has been used previously to determine each instar  be misleading  information  for each  in the last 2 instars; it should  sex, to improve the accuracy of the  heavier  of duration of the 5th and 6th  instar  may  separate  their  determination.  sex.  Similarly, head-capsule (Raine  1966),  also be measured for each  IV. INSECT THERMOREGULATION  A. LITERATURE REVIEW  Insects have a relatively large surface to volume ratio and therefore  may  lose heat and water to their environment in amounts that can be detrimental. Often,  therefore,  their  survival  depends  on  their  ability  to keep  their  body  temperature and water content within safe limits by balancing the losses against the gains. Several characteristics of both the environment and the insect affect its ability to achieve these thermal and water balances.  Since  an insect's  water  content constitutes  50-90%  of its body  weight  (Chapman 1982), it is faced with the problem of retaining water or replacing the losses. Relative humidity of the air surrounding an individual is modified by air temperature, wind dependent factors.  on  speed  and solar radiation. The effects of these are i n turn  the individual's  In general,  larger  size, the permeability insects  lose  less  water  of its cuticle, than  smaller  and other ones.  The  permeability of the cuticle is well correlated with the habitat (Bursell 1974a) as the less permeable ones are found in xeric environments and the more permeable ones in more humid milieux. Thermal and water balances are not independent of each other; many mechanisms used to regulate high body temperature will at the same time decrease the water losses.  Insect body temperature (T ) is dependent D  on two factors: (1) changes i n  the production and internal distribution of metabolic heat, and (2) alterations of  35  36 heat exchange  with the environment.  1. Regulation of metabolic heat  When the air temperature (T ) is low, winged insects increase their body a  temperature by producing metabolic heat, often by contracting their flight muscles. Since the ability  to fly depends on muscle  temperature, when  T  a  is low a  warm-up period (shivering) during which flight muscles are contracted is necessary to  increase thoracic temperature ( T ^ ) ; e.g., the hawk moth, Deilephila  "shivers" to achieve the narrow  range  of 32°-36°C needed  for flight  nerii L., (Dorsett  1962). Similarly, Heath and Adams (1965) reported that the sphinx moth, Celerio lineata Fabr., stabilizes its thoracic  temperature  during  flight  over a range of  ambient temperatures; i.e., it achieves some endothermic regulation.  Bees also increase  by shivering. The bumblebee Bombus vagans Smith  can forage for nectar at temperatures ranging from 5°C in the shade to 31°C in sunshine (Heinrich 1972a). While sitting on flowers at T < 2 4 ° C a  it maintains  a thoracic temperature close to 32°-33°C, the minimum temperature required for flight. When T > 2 4 ° C , regulation of thoracic temperature ceases and T^h rises. a  Similar endothermy has been demonstrated in other bumblebee species, notably B. terricola Kirby, B. edwardsii Cresson and B. uosnesenskii Radoskowski  (Heinrich  1972b,c). Heinrich (1972c) found that in some species T ^ was regulated, but the abdominal temperature was not and varied with T . A queen, however, seems to a  control heat transfer from the thorax to the abdomen, as she heats her brood primarily through her abdomen even though  heat is produced  exclusively in the  37 thorax  (Heinrich 1972d). Heat transfer to the abdomen also takes place i n the  dragonfly  Anax  Junius  (Drury)  (May 1976b)  and modification  of abdominal  haemolymph circulation seems to be involved i n the control of heat loss by the abdomen.  Thermoregulation several  is a complex process  variables. Insulation or high  size (McNab 1970)  metabolic  determined  by the interaction of  rates can compensate for small  but in general the rates of cooling of a small insect are too  high to allow substantial endothermy to occur (Heinrich 1974). Therefore for most insects, body temperature, mechanisms  used  determining  T , is dependent on T D  a  (depending on the behavioural  to control T ) and habitat selection D  the conditions of temperature and humidity  becomes  important in  to which the insect will  be subjected.  2. Heat exchange with the environment  Insects  can exchange  convection, radiation mainly with  through  (Digby  with  and evaporation.  radiation  (Parry  increases in solar radiation  convection and  heat  1951)  the environment  through  conduction,  In most environments, insects gain and body temperature  heat  increases linearly  (May 1979). Insects lose heat principally by  1955). However, the effects of various sources  of heat gain  loss depend on characteristics of the insect itself, such as its size, surface  area, colour, geomet^ and the microsculpture of its surface area.  For  a given size (volume), insects with greater surface area will have a  38 greater exchange  of heat and water with the environment, whereas for a given  surface area, large insects (bigger volume) will have a greater rate of heat and water exchange  than smaller insects. Large insects attain a higher temperature  excess (T^ - T )  than small insects but take longer to reach it under constant  conditions (Digby  1955, May  a  because  1976a,  Willmer and  their body temperature changes  Unwin  1981). Large  insects,  more slowly than that of small insects,  can tolerate less stable environments and intermittently higher radiation than the latter. Furthermore, large  individuals can  become active  at cooler temperatures  than smaller ones can because of the greater temperature excess the former can achieve. However, large insects must avoid constant high radiation which  could  lead to overheating (Willmer 1982). Colour and texture of an insect's surface also influence its thermal balance. In fact, insects of higher reflectivity slowly than dark forms of the same size (Willmer and Unwin being better  heat more  1981), the latter  "black bodies". Surfaces bearing hairs, bristles, scales, etc., reduce  the loss of heat and water by holding an insulating layer of air adjacent to the body. In dragonflies, the layers of air-sacs at the surface of the thorax provide such an insulation device (Chapman 1982).  Many  insects  can  exert  some  control  in  maintaining  their  body  temperature within the preferred range by means of behavioural mechanisms (see review  by  Casey  1971)  Several  species  need  to  attain  a  minimum  body  temperature in order to start activity. Body temperature can be raised above air temperature through radiative heating by exposing the largest surface of the body perpendicular Schistocerca  to the gregaria  sun's  rays.  (Forsk.),  lies  At  low  air temperatures  on  its side  so  that  the  desert locust,  its lateral  surface is  39 perpendicular hybrida  to the sun's  rays  (Chapman  1982). The  tiger  beetle,  Cicindela  L., rests on a slope with its back perpendicular to the sun and the  underside of its body on the warm well as by radiation  (Dreisig  sand, thus gaining heat by conduction as  1980). Insects can also orient themselves to the  wind to increase or decrease heat and water losses. A s the body warms up, the insect needs to minimize heat input and adopt different postures; e.g., S. gregaria then faces the sun, thereby minimizing the surface area intercepting radiation. A t higher temperatures, both S. gregaria and C. hybrida extend their legs vertically under the body, thus lifting it away from the hot surface and increasing heat loss by convection. If the temperature excess is still too great, they move to a cooler microhabitat. For example, when overheated, C. hybrida buries itself in the sand,  whereas  S. gregaria  seeks  shade  or  moves  above  the ground  onto  vegetation where convective and evaporative heat losses are increased by stronger wind. In the evening when temperature falls, S. gregaria crouches to the ground, gaining heat by conduction (Waloff 1963). This last behaviour can also serve to lose heat to a cooler soil (Gamboa 1976).  Evaporation may be the greatest source of heat loss in stationary insects (Chapman 1982). This heat loss, due to withdrawal from the body of the latent heat of vaporization, can be increased by low humidity, high temperature and wind. Individuals surface  of some  to volume  ratio  clustering  permits some  metabolic  heat  (Willmer  species  tend to aggregate, decreasing their  and thereby increase  is shared  minimizing water  i n body  and conserved  temperature while  and heat  effective  loss. This  without detriment since  convective cooling  1982). In winter, bees cluster together when T < 1 5 ° C a  is reduced  and maintain  40 the  temperature  mechanism  used  of the cluster  at  to regulate water  20°-25°C  via metabolic  heat.  Another  loss consists of closing the spiracles when  conditions become potentially too harmful.  Another  type  of posture  is exhibited  Dythemis  cannacrioides  Calvert  pointing  the abdomen  toward  posture"  and shading  the thorax  Pachydiplax period  longipennis  on perches,  decrease  by  the incidence  the sun in a with  some  relies on the obelix posture  of solar  position referred  the wings  (Burmeister), a dragonfly  dragonflies. Males of  (Gonzalez  radiation by to as "obelix  1987).  Similarly,  that spends, most of its active to minimize  solar heating. In  addition, it perches horizontally with the long axis of the body perpendicular to the  sun (May  thermoregulates  1976b). simply  This by  species  adopting  does  not usually  different  postures.  seek  the shade and  In sunlight, its body  temperature is relatively independent of ambient temperature during most of the day.  An Malacosoma not  interesting disstria  be overheated  mechanism  exists  in larvae  of the  tent  caterpillar,  Hbn., that insures, among other things, that the larvae will (Sullivan  and Wellington  1953). Below  a  certain range of  temperatures, the larvae are photopositive and therefore sit in the sunlight on the  leaves.  When  their  internal  temperature  is raised  above  this  "reaction"  temperature, the larvae cease to be photopositive and seek the shade on the undersides  of the leaves. If their body temperature  in the shade drops below  their reaction temperature, they become photopositive again. In fact, i n marginal situations - e.g., hot sun and cold air, - larvae may  move continually between  41 the two sides of the leaf until they  locate an appropriate zone in which  they  can rest.  Basking temperature  is common i n butterflies because they  for flight.  Basking  allows  need a minimum thoracic  the butterfly  Argynnis  paphia  L. to  maintain  a body temperature of 32°-37°C. The position of its wings plays an  important  role in regulating the absorption of solar energy. To gain heat, the  insect exposes itself to the sun with opened wings. When its body temperature is too high, it closes its wings completely Heodes virgaureae  L. exhibits  a  or else seeks shade (Vielmetter 1958).  similar  behaviour  (Douwes  1976).  In sunny  weather, it directs the upper surface of its body toward the sun and the angle between its wings is inversely related to air temperature and solar radiation. The butterfly Calisto nubila L., a lateral basker, keeps its wings dorsally  appressed  while basking and exposes the side of its body to incident solar radiation (Shelly and  Ludwig  1985). By tilting  its wings  to keep  them  perpendicular  to the  incident solar radiation, it elevates its thoracic temperature faster and reduces the time spent basking. Females of the speckled wood butterfly, Pararge aegeria (L.), bask  for longer  maturation  periods  than  male  conterparts, thereby  accelerating egg  (Shreeve 1984). Flight i n this species results in significant convective  cooling and can be used cooling in Precis villada convection  their  as a method of reducing  T . Flight also results in D  F. (Heinrich 1972a). Church (1960) showed that forced  is the primary  avenue  (1985a,b) described a new basking  of heat  loss in flying  posture, called  insects.  Kingsolver  reflectance basking, i n which  the wings are used as reflectors to reflect solar radiation to the body instead of absorbing it. This posture was described for four species of Pieris.  42 Immature subject  dragonflies, having an incompletely  to excessive water  loss,  seek  shady  hardened  and cool  cuticle  areas  and thus  (May 1976b).  Similarly, i n some butterflies, survival of eggs and larvae is decreased in sunny habitats (Rausher 1979) as compared to shady ones. Many insects regulate their activity  in such  (Willmer  a way as to avoid extremes  1982). The tenebrionid  Eleodes  beetle,  i n temperature  obscura  and water  loss  (Say), decreases water  stress by restricting its activity to periods when the heat load is minimal or to microclimates thermally  that  are moist  and cool  (Marino  1986).  Flower  favourable floral microclimates and avoid thermally  mites  exploit  adverse conditions  within inflorescences, and they may disperse to different flowers by hopping on the  bill of hummingbirds  visiting the flowers (Dobkin 1985).  3. Microclimate  Until  Uvarov's  major  review  of climate  and  temperatures and humidities in insect habitats were often same as the ambient air. Uvarov of  insects assumed  (1931), the to be the  showed that standard meteorological data were  little use to ecologists, as they bore only a distant and indirect relation to  the  microclimates where  insects  insects' microclimates. Wellington  lived.  He  encouraged  entomologists to study  (1950) was one of the first  entomologists to  investigate environmental differences among small-scale microclimates. He studied the  temperature  of different  components  of a conifer  and a broadleaf tree,  measuring the surface temperatures of foliage and bark of twigs as well as the internal temperatures of vegetative buds, expanding shoots and staminate cones under  different  weather  conditions.  During  a  clear  day, the temperature of  43  exposed foliage is higher than the air temperature. Radiation plays a major role since  foliage  temperature radiating  exposed than  to clear  skies  but shaded  the air. A t night,  from  the exposed  to the sky, and becomes colder than  overcast does not change foliage temperature  the sun has a lower  foliage  loses  its heat by  the surrounding air. High  thin  significantly but a heavy overcast  may decrease the difference between the foliage and the air. Dense clouds reflect and  re-emit enough  slightly small  above  radiation  to keep  the temperature  air temperature. Whenever  variation  in cloud  thickness  overhead  clouds affect provokes  of the exposed foliage  foliage  temperature, a  an immediate  change in  foliage temperature.  In  winter, a snow-covered  branch reflects part of the incoming radiation,  thereby preventing the branch from becoming warmer than air temperature. A t night, this snow-covered exposed  branch, being insulated, does not lose as much heat as  surfaces and often stays warmer than the surrounding air. However, i f  there is room for passage of air currents underneath it, its temperature can fall to the air temperature. (Wellington 1950).  Just  as the angle  at which  an insect  is exposed  determines its T , the angle at which a surface is exposed D  to solar  radiation  to solar radiation is  also important. Wellington (1950) found that, at air temperatures varying 15°-26°C, aspen  leaves hanging  vertically  had a  temperature  from  of 0.5°-1.6°C  higher than the air temperature, while coniferous foliage exposed more directly to the  incoming radiation reached temperatures between 1.6°-8°C higher than that  of the surrounding air. Furthermore, an aspen  leaf rolled by a tortricid  larva  44 and  maintained  radiation  than  at an angle  of 40° to the sun, thereby  an undamaged leaf, had a temperature  intercepting  comparable  conifer foliage (Wellington 1950). Similarly, Henson and Shepherd  more  to that of  (1952) found, at  air temperatures varying from 25.3° to 24.6°C, that the temperature of the flat lower surface of a lodgepole pine needle was 4.5 °C the  needle  was parallel  to the sun's  rays,  higher than the air when  and 7.9°C higher when  i t was  perpendicular to the incoming radiation. In contrast, outgoing radiation did vary significantly with the angle of the exposed  foliage; e.g., normal  not  aspen and  coniferous leaves, which are at different angles, have about the same temperature during the night.  Rain does not directly alter foliage temperature. However, when the water present on the foliage  starts  decrease i n temperature  evaporating, the foliage  temperature  drops. This  is due to the loss of heat necessary to vaporize the  water. This effect of rain is common to both day and night conditions.  During warmer  than  a  clear  night,  vegetative  buds,  coniferous staminate and by  cones  are from  day can frequently  5°-8.4°C  be as much  10°-14.5°C above the air temperature. Under a polar air mass, or under clouds, the flowers have temperature  a slower cooling  rate  than  the buds.  as  broken  Although the  differences between the stem, flowers, vegetative buds and ambient  air vary for each  tree species, Wellington (1950) showed that the tendency of  the flowers to be warmer than the buds was consistent for white spruce (Picea glauca Voss), balsam Lamb.).  fir (Abies balsamea Mill.) and Jack pine (Pinus  Banksiana  45 The  length of time during which  one part of the tree is exposed to the  sun's rays has an important impact on the temperatures  reached by the various  sides of the tree throughout the day. Peterson and Hauessler (1928) and Haarlov and  Petersen  (1952)  determined  15°-20°C could be observed trunk. Lewis and  that  temperature  differences as  as  between the north and the south sides of a tree  (1962) reports similar findings. Such studies (Lewis  Haeussler  great  1928; Haarlov  and Petersen  1962, Peterson  1952; Wellington 1950) showed  how  different the microclimates in a very small space could be.  Immature from  insects  are often unable  to move  great distances or disperse  the site where they hatch. Their survival therefore depends largely on the  choice of a proper habitat by ovipositing females seeks  out a  Euphydryas  favourable  gillettii  microclimate  (Inoue  to oviposit  Barnes (Williams 1981).  1986). One insect that  is the montane  butterfly,  Its egg masses are located on the  undersides  of the uppermost southeast-facing leaves of its host shrub,  involucrata  (Rich.). These leaves are perpendicular to the morning sun and are  warmer  at  demonstrated  that  time  of  day  than  differently  oriented  leaves.  Lonicera  Williams  that the egg masses present on the leaves perpendicular to the  morning sun hatched  on average 6.1 days earlier than  those on leaves parallel  to the sun's rays. As the mornings in the study area were usually clear and cold  and  the  afternoons  warmer  and  partly  or  entirely  cloudy,  advantageous for the eggs to be subjected to higher temperatures  it was  early in the  day. This thermal advantage is important for this species since the larvae must develop to their second as  instar (their diapausing stage) when temperatures  low as -5°C. The tiger  swallowtail, Papilio  glaucus  can be  L., also selects  sites  46 exposed  to the sunlight for its egg masses (Grossmueller and Lederhouse  1975).  Larvae in sunny exposures developed 15-35% faster than laboratory-reared larvae lacking radiant input. Increased developmental rates allowed the completion of a second generation in some areas.  Instead survived shelters  of seeking out favourable climatic  detrimental which  or  provide a  conditions, some insects  unfavourable temperatures favourable microclimate.  and The  humidities  by  have  creating  microclimate present in  bags built by the evergreen bagworm, Thyridopteryx ephemeraeformis  (Haw.),  was  investigated by Barbosa et al. (1983). It had been previously suggested that the role of the evergreen bagworm's shelter was  to offer protection against predators  and parasites (Sheppard and Stairs 1976, Davis 1964). On trees  where  the  average  air temperature  study, the temperature within a bag was the ambient air. On  the shaded  higher than the average  was  34.34°C  the exposed during  the  period  of  on average some 3.29°C higher than  side, the internal bag temperature was  air temperature  side of  (31.57°C). Therefore, on  the  0.79°C exposed  side of the tree, the shelters have a temperature 4.67°C higher than those on the shaded side.  Barbosa et al. (1983) did not find any temperature difference between the surface  of the bag  and  its interior. Furthermore, there was  no  evidence that  metabolic heat might be partly responsible for heating of the bags. It seems that the  higher  temperature  inside  properties; i.e. their dark color.  the  bags  was  due  solely  to  their  physical  47 Shelters built by insects may surrounding casemaking  the  occupant.  In  also modify the moisture content of the air  its natural  setting,  clothes moth larva, Tinea pellionella  the  microhabitat  of  the  L., is composed of a hygroscopic  case made out of silk and muskrat hair. This kerophage larva is able to develop at  any  humidity levels including  bearing and caseless T. pellionella weight change. A t 100%  0%.  Chauvin  et al. (1979) placed both case  larvae at various humidities and recorded their  relative humidity, the weight of the larva with its case  increased and stabilized at a level 3 0 % higher than its initial weight, whereas in the  absence  of the case, the gain  fairly stable. A t 9 5 %  R.H.,  was  reduced  so that the weight  the same phenomenon occurred for larvae in cases;  but for exposed larvae, weight fluctuated more than for larvae at 100% not stabilize but tended to drop slowly due 55%  R.H.,  as for those with cases. The  larval case provides a  air and  twice as great  more humid  environment  thus is a major adaptation, especially  arid conditions. In very moist conditions however, its beneficial role may weighed  under be out  (literally) by its heaviness. In a permanently saturated atmosphere, many  larvae cannot carry their heavy new  and did  to evaporation of body water. A t  the rate of weight loss of larvae - without cases was  than that of the ambient  remained  water-logged cases, so they desert them to build  ones.  Among insect-created microhabitats, the webs of tent caterpillars provide very sophisticated climatic control. The tent of Malacosoma pluviale (Dyar) acts as a greenhouse  raising the enclosed air temperature much higher than the outside  air  temperature (Sullivan and Wellington 1953). The  by  the addition of new  rooms, all connected by  tent is continually small holes. The  expanded  temperature  48  may  vary  widely  from  one  pocket  to  another  radiation or shade that each receives. The comfortable temperature. The vapor,  thereby  ensuring  the  inside  moisture comes from water that has as from their frass and  On  larvae may  silk walls of the  that  depending  of  on  amount  tent  passage of water  is always  moist.  This  evaporated from the insects' bodies as well  exuviae.  a cloudy day, after their first morning feeding period, the larvae  return to the  of  therefore choose the most  tent slow the the  the  tent or stay at their feeding  may  site where the}' remain inactive. If  they return to the tent, they rarely enter it immediately, but rather rest on its surface  or near it. On  a clear day,  re-enter  their tent after their  due  a  to  Wellington whereas on  response  to  1953). During cloudy  however, all the larvae return rapidly to  first  feeding  evaporation  rather  dry  period. This than  clear days, the  to  behaviour seems to  temperature  larvae  need  the  (Sullivan tent  be and  moisture,  days, outside humidity is sufficient. These different behaviours  do not seem to be temperature-related, or warmer than clear ones. As  since many cloudy  mornings are as warm  long as the humidity is high, the larvae do  not  enter the tent.  Solar  heating  reaches  a  maximum  However, the air usually becomes drier and  at  midday  and  decreases  hotter for a few  afterward.  hours after noon.  During that period, the larvae that are in the tent move to cooler pockets until mid-afternoon, when even the coolest may larvae  emerge quickly to rest on  outside  air temperature has  the  become too hot. Then the overheated  tent's outer  begun to drop and  surface.  By  that  time  is more tolerable than any  the of  49 the temperatures inside the tent.  Henson modifications  (1958b) of  poplar  studied  the  thermal  He  measured  leaves.  effect the  of  insect-caused structural  temperature  of  a  normal,  unmodified poplar leaf and compared it to that of leafrolls, leaf mines, galls, etc. that had been made by insects using poplar leaves. He  found that the shape of  the structure, air circulation at its surface or within, surface-volume ratio, colour and  absorptivity  all affected  the  structure's  temperature.  In  microhabitat studied, the temperature never reached the extreme the  exposed  Choristoneura a  surface of an conflictana  strong heating at  temperature  undamaged  leaf.  For  example,  levels  of solar  radiation  but  every  values found on  in the  (Wlk.) rolls were built in such a way lower  almost  field  most  that they provided a  relatively  stable  at high levels of radiation. This allowed the insects to be  active  under  moderate insolation when the ambient  below  their "physiological zero", but kept them from being overheated when the  radiation intensity was  Maximum  temperature was  often considerably  very high.  radiant heating was  found  in structures  such  as  leaf  mines,  where air is stabilized in thin layers between thin sheets of tissue and  where  the air spaces are comparatively small. Minimum radiant heating was galls, where a large volume of air is partially  enclosed by  tightly  found in packed  or  dense tissue (Henson 1958b).  differ  Since  Uvarov  from  the  (1931)  ambient  pointed out  that  air temperature,  temperatures  microclimatic  where  studies  insects have  live  become  50 increasingly Ruesink  important  1976; Ferro  microclimates sampling,  shelter-building  where  research  et al. 1979).  Y e t many  and microclimate-related behaviours  monitoring,  behaviour  i n entomological  spraying  insects,  or  one should  (Peterson  entomologists  when they  modelling  and Wolfe 1956; neglect  design programs for  populations.  not neglect  still  possible  Especially  links  with  between the  of the insect, the characteristics of its life cycle, and the microclimate  i t lives.  microclimate  The study  present  reported  in the leaf  here  is an  shelters built  attempt  by the larvae  to describe the of Cheimophila  salicella (Hbn.) and its relation to the insect's developmental rate.  B. MATERIALS AND METHODS  The  microclimate  study  was conducted  i n the high-bush blueberry  field  described in Chapter II. Leaf shelters on three bushes (Rubel variety) i n the last southern  row of the field were used, as their south sides were well exposed to  the sun and any temperature differences between the inside of the shelter and ambient  air would be evident. Sixteen  shelters were chosen from  a l l cardinal  quadrants of the bushes (north, east, south, west). Each shelter was assigned to one of the following categories: a) two green leaves tied together  (G/G); b) a  reddish-brown dried leaf tied onto a green one (R/G); and c) a green leaf tied onto a dried one (G/R). A i r and shelter temperatures were measured hourly over a 24h period, whereas hourly measurements of photosynthetically active radiation (PAR) were taken  only during daylight. P A R is directly  related to total  solar  radiation (Howell et al. 1983) and therefore is a good estimate of solar radiation. For  a detailed  study  of a particular  shelter, temperature  measurements  were  taken  in  on  days  5  rapid  from  f r o m overcast comparison: cloudy were  succession J u l . 29  following  to  to clear and  clear  conditions taken  concurrently  from  29,  (Aug.  3  about  0800h  In  one  Aug.  (day  only),  under  given  only),  and  (standard  weather  Aug.  Aug.  time)  (wire  one  Aug.  only).  morning  to  made ranging  17)  were  and  Measurements  about  the beginnings of each  measurements  arc-welded  shelter. One  were  mm)  Northrup and  was  made  connected  0700h  made 24h  the  was  possible  as  close  as  the study  5th- or  with  the  only  from  period  when  via  copper-constantan  a  switch  a  mercury  Celsius.  were  the  other  leaf shelter. T h e y  and clothespins. The  a The in  assigned  the shelter, in the silk tunnel,  outside  to  thermometer  thermocouples  6th-instar l a r v a . The  w i t h hairpins  box  8692-2) reading i n degrees  calibrated against  inserted inside  one of the openings left by  place throughout  conditions  and  (day  7, measurements  mark  diameter = 0.0 76  were  positioned  14,  7  a bath of water held at different temperatures. Two to each  were  were taken.  portable potentiometer (Leeds & thermocouples  1985  instance, A u g .  temperature  thermocouples  3  (night  0 9 0 0 h to 2200h. The dates the measurements  18,  radiation. M e a s u r e m e n t s  w a r m . These days were divided into 2 categories for  (Jul.  morning.  The  Aug.  with  through  thermocouple were  held  thermocouples  in  were  left in place throughout  the investigation a) to minimize disturbance of the l a r v a ;  b) to m i n i m i z e the risk  of b r e a k i n g  shelter  by  standardize Li-188B was  moving the  the  open  or  modifying  and  c)  to  thermocouple;  data-collecting procedure.  quantum/radiometer/photometer  generally  held  perpendicular  to  minimize  Radiation reading  the  the  in  was  handling  measured  /uEm  shelter, but  characteristics of the  was  _ 2  time with  and a  Li-Cor  s- .  The  held  perpendicular  1  to  instrument to  52 the sun when at least a portion of the shelter was directly facing the sun.  The  results from  3 sets  of thermocouples which  measurements at low temperatures had to be discarded.  did not give  accurate  Consequently, 13 shelters  provided the bulk of the readings; 3 in the north quadrant, 5 in the east, 4 in the south and 1 in the west. Two or three thermocouples functioned  improperly  for short periods of time (from 2h to 1 day) but seemed in order later. It is possible that the insect's presence in the shelter occasionally  interfered with the  proper functioning of the thermocouple.  Correlation amount  analysis  of radiation  temperatures climatic  (Reg Procedure,  and the difference  was conducted  conditions  for sunny  and the type  SAS  Institute  between  and cloudy  of shelter  1985) between the  the shelter conditions.  on the daily  and the  air  The effects of  maximum  T  e x c e s s  (difference between air and shelter temperatures) of each unit were analyzed by analysis of variance was  ( G L M Procedure, S A S Institute, 1985). A separate A N O V A  used to assess the effects of the cardinal location of the shelters on the  maximum included  T  e x c e s s  .  In this  because only  A N O V A , the data  one shelter was located  the same factors on the nocturnal way.  Only the minimum T  e x c e s s  minimum T  for the west  side  were not  in this quadrant. The effects of e x c e s s  were analyzed in the same  occurring between 2000h and 0200h was used  in this analysis because the sky started to clear around 0200h on the "cloudy" night.  Among  the "clear"  ^excesses occuring  nocturnal  readings,  only  5  of the 26  minimum  between 2000h and 0200h did not correspond to the T  e x c e s s  for the entire night. A significance level of 5 % was adopted for all analyses.  53 C. RESULTS  The  summer of 1985 was very warm and dry. In July, only a trace of  precipitation was recorded for the whole month. The warm and sunny trend set in July continued in Aug. despite the fact that some cloudy and wet days were present at the beginning of the month. Sunshine precipitation  in Aug. was well above normal,  was below normal and air temperatures  were near  normal.  As a  result, more clear days than cloudy ones were available for investigation. Of the 4 clear days, July warm  and had very  29, Aug. 3, Aug. 14 and Aug. 17, the last 2 were very few i f any clouds. On  clouds were present on July Aug.  the other hand, some high thin  29 and again on Aug. 3. During the evening of  3, the clouds thickened to an overcast during the night. Daytime cloud was  present on Aug. 7, but the overcast began to break  up around 2200h, so no  further nocturnal readings were taken past that time. Although  the weather on  July  29 might seem to a casual observer to be relatively clear, the results for  this  day will  be discussed separately and were  not included in the analysis.  Clear conditions refer to Aug. 3 (day), Aug. 14 and Aug. 17, whereas cloudy ones refer to Aug. 3 (night) and Aug. 7 (day). A the  climatic  conditions  presented in Table I.  prevailing  in the  field  more detailed description of  during  the measurements is  54 T A B L E I. Weather during the days when the microclimatic measurements were taken in a high-bush blueberry field in Richmond, B.C. in 1985.  WEATHER CONDITIONS  REMARKS  Sunny and warm High thin clouds Next morning: cloudy  21h00 OlhOO 05h00 06h00 07h00  Aug. 3  Sunny with high clouds Clouds thickening in evening Night: generally overcast, some wind Next morning: sunny  18h00 19h00 20h00 22h00 02h00  Aug. 7  Cloudy with isolated showers Some sun in the afternoon  lOhOO overcast, some raindrops llhOO wind, some sun 12h00 partially sunny from here on 22h00 mainly clear, some fall-out raindrops  Aug.  Sunny day Little or no clouds Clear night, warm and damp Next morning: sunny  23h00 warm breeze 04h00 breeze  Sunny and warm, no clouds Night: foggy with clear sky Next morning: sunny  03h00 foggy 07h00 clouds  DAY  JL  29  14  Aug. 17  Standard time.  1  inversion wind wind clouding over clouds  clouds (until about 02h00) wind wind rain clearing up slightly, no more wind 07h00 cloudy 08h00 some sun  55  1. Clear conditions  a. Solar  radiation  On  clear  between  6h00  between  0900h  days, the solar (STD  time)  and  and  1300h  and  occur as fast as the morning  MEm  _ 2  during  Between  1800h  s  Aug.  _ 1  .  On  which  0900h.  0600h  were  level  reached  decreased. The  radiation 17  levels  were  a  decrease  The maximum  //Em" s " ') was  received  2  usually  (Fig. 10a), the two  made, the average  2  (2510  radiation  subsequently  between 1900 and 2000 juEm" s " measured  The  (Fig. 9a) and  measurements  (Figs. 8a, 9a, 10a) increased  rapidly plateau did not  increase.  and 14  radiation  by  a  radiation  below  250  sunniest  days  at midday  was  amount of incoming radiation green  shelter  in the south  quadrant at 1300h on Aug. 7.  b. Shelter  and  The  air  temperatures  air and  shelter  temperatures  followed  very  similar  patterns  over  a  24h period (Figs. 8b, 9b, 10b). In the morning, temperatures started to rise near 0600h.  The  whereas that  maximum  temperature  inside  the  shelter  of the air occurred 2 hours later around  both  temperatures  Aug.  14  decreased  (Fig. 9b) minimum  and  reached  average  their  shelter  occurred  around  1300h  1500h. In the afternoon,  minimum  temperature  values was  at night.  On  recorded between  FIGURE 8. Average radiation levels (a), air and shelter temperatures (b), and ^excess ( ) measured August 3, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.) c  o n  to  o <  o o ^  UJ  or UJ  i—•—i  9-. 6H IS 10  3H  -3 8  1  ' 1 ' 1 ' 1 ' 1  r-  T  10 12 14 16 18 20 22 24  TIME (HOURS)  '  1  2  '  1  4  '  1  6  '  1  8  58  FIGURE 9. Average radiation levels (a), air and shelter temperatures (b), and ^excess (°) measured on August 14, 1985 in a high-bush blueberry Field in Richmond, B.C. (Bars represent SEM.)  60  FIGURE 10. Average radiation levels (a), air and shelter temperatures (b), and excess ( ) measured on August 17, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.) T  c  62 2300h  and  OlOOh  temperature was  the  following  measured  day,  whereas  at OlOOh. On  Aug.  the  minimum  average  3 (Fig. 8b) and  17  air  (Fig. 10b)  minimum average temperatures for both shelter and ambient air occurred between 0400h and 0500h. On the  shelter  Aug.  17,  ranged  was the  33°C  whereas  maximum  between  34°  it was  average  and  temperatures on Aug. which had  Aug. 3, the maximum average temperature recorded inside  36°C  30°C  temperature  in the  air. On  in the  shelter  was  average  shelter  in the air. Minimum  14 were around  11°C  a cooler night, the shelter and  and  12°C  Aug.  14  and  39°C, but  respectively. On  air temperatures were 3°C  and air Aug.  17,  and  4°C  respectively.  As  noted,  the  shelter  temperature  ambient air in the morning and temperatures about  0800h  were to a  increased  after  than  started to decrease earlier. On  above those of the ambient little  faster  the maximum  air for almost  air temperature  that  of the  average, shelter 8  hours, from  was  reached  at  about 1600h. After that, however, and until 0800h the following morning, the air was  warmer than the shelter.  The In  the  pattern  morning,  of shelter and both  temperatures  (compare Figs. 8b, 9b, 10b there was  air temperatures resembled  and  increased  as  radiation  that for radiation. levels  increased  Figs. 8a, 9a, 10a). In the afternoon, however,  a time lag of 1 to 2 hours between the decrease in solar input  the subsequent decrease in shelter and air temperatures.  and  63 In spite of the high temperatures that were occasionally  recorded  in the  leaf shelters, most larvae remained in their shelters at least until the end of the observations  on Aug. 17. A t that time, it was impossible  occupant was still present  to tell whether the  in 1 of the 13 shelters, but another had definitely  been abandoned. It was not clear whether the shelter had been deserted because of  excessive  Although  heat  no  or because  mass  exodus  extensive  feeding  of the larvae  had rendered  occurred  during  i t unacceptable. periods  of high  temperatures, a larva inhabiting a south-facing R/G shelter kept its head outside the shelter during the high-temperature period on Aug. 17.  c. Differences  The  between shelter and  difference  and radiation  e x c e g s  explained  by  increased, T response  temperatures  between shelter  closely followed radiation T  air  radiation  patterns (Appendix  and air temperatures  (Figs.  8a, 9a, 10a).  I) showed  (F = 401.12,  that  df= 1,563).  (Figs.  soon  e x c e s s  could be  as radiation  levels  increased. There was no time lag such as the one in  e x c e s s  of shelter  and air temperatures  10c)  The correlation between  41.5% of T  As  8c, 9c,  to a decline  in radiation.  T  the  e x c e s s  decreased when radiation levels decreased.  As Daytime T  would be expected, T e x c e s s  e x c e s s  was greater during the day than at night.  could be as much as 16°C, although  on average the maxima  were between 6° and 7°C. A t night, when there was no solar radiation, the air temperature was about 2°C warmer than that of the shelter.  64 The  maximum  T  e x c e s s  reached  and the amount of time  greatest varied between shelters. Figure R/G shelter  facing  northeast  T  11 shows the changes in T  on Aug. 17. This  shelter  e x c e s s  e x c e s s  was exposed  was for a  to early  morning sun for a relatively short period and was shaded by an adjacent bush during most of the day. T  e x c e s s  increased  very  quickly  early  peaked at 14°C around 0900h, and decreased quickly to reach 3°C  by llOOh, finally reaching 0°C by 1600h. Although  was  above that of the air for 8 hours, the values of T  i n the morning, a low value of  the shelter temperature e x c e s g  were high  only  south-facing  R/G  during the first 3 hours.  For  comparison, Figure  shelter for the same date. This  12 shows  the T  e x c e s s  of a  shelter was not shaded by adjacent  leaves or  bushes and therefore was well exposed to the sun during the entire day. T of this  south-facing shelter did not rise as fast as that of the shelter  northeast; e.g., at 0900h  the south-facing  shelter  had a T  e x c e s s  plateau  between  decreased quickly  inside of the shelter.  e x c e s s  of  to rise to about 14°C at lOOOh. It reached a  1000 and 1400h, with after  facing  of only 7°C  compared with 14°C for the northeast shelter (Fig. 11). However, the T the south-facing shelter continued  e x c e s s  1400h. B y about  a maximum  of 16°C at 1230h, and  1600h the air was warmer than the  65  F I G U R E 11. R a d i a t i o n levels (a), and T (b) measured shelter made of one green and one red leaf i n a high-bush Richmond, B.C. on A u g u s t 17, 1985. e x c e s s  for a northeast-facing blueberry Field in  67  F I G U R E 12. Radiation levels (a), and T (b) measured for a south-facing shelter made of one green and one red leaf in a high-bush blueberry field in Richmond, B.C. on August 17, 1985. e x c e s s  69  2. Cloudy conditions  a. Solar radiation  The  daily pattern of solar radiation (Fig. 13a) under the cloudy pattern  that occurred during the observation period was similar to that under clear skies, but levels attained below  were lower. The average  1500 j i E m ^ s "  maximum  average  relatively  high  1  and peaked  radiation  (1383  ±  level  levels on Aug.  at 1387 A i E m - s 2  which  occurred  251 j i E m s " , _ 2  radiation  1  mean  _ 1  at 1300h ±  7 were  at 1200h. The on Aug.  7 was  S E M ) due to intermittent  sunlight.  b. Shelter and air temperatures  The generally  patterns of shelter  and air temperatures  on Aug.  cloudy day, were similar to the patterns exhibited  gradual increase until  7 (Fig. 13b), a on clear days: a  approximately midday, followed by a decrease, however,  temperatures did not reached the high levels measured on clear days. Maximum average  shelter  and air temperatures  were  26 °C  (at  1300h) and 25 °C (at  1500h) respectively. Although these maxima were lower than those recorded on clear  days,  their  temperatures  were  time 13 °C  of occurrence  remained  for the shelters  and 14°C for the  minima were recorded at 2100h, no subsequent the sky was clearing. The  the same.  Minimum air. After  average these  measurement was taken because  average shelter and air temperatures recorded at night  70  F I G U R E 13. Average radiation levels (a), air and shelter temperatures (Jo), and ^excess ( ) measured on August 7, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.) c  I  o < -i—-—i—•—i—•—i  Legend  B  o  shelter  30  o  !<  Cr: UJ Q_ Z£ UJ  20  •i  olr  H  10 H -,—.—r—.—i—•—i—>—i—-•—i—•—i—•—i  0  •i  9  6-  in v\  3-  o X  0-  -3  • — i — i — i — i — | — > — i — i — i — • — i — i — i — i — i — i — i — • — i — • — i — i — |  8  10  12  14  16  18  20  22  24  TIME (HOURS)  2  4  6  8  72 under  cloudy  conditions  on Aug. 3 (Fig. 8b) remained  16°C)  until the clouds started to break up around 0200h.  relatively high  (about  c. Differences between shelter and air temperatures  The  values of T  e x c e s s  were significantly affected  by radiation  (F = 60.43,  df= 1,129) (Appendix II) although radiation explained a smaller  proportion  variation in T  e x c e s s  day that  e x c e s s  (31%)  than it did on clear days (41.5%). T  was significantly reduced under  clear  skies.  occurring quite  during the  (F= 17.88, df=l,45) (Appendix III) compared  The average  5 ± 0.7°C compared with  of the  maximum  value  of T  e x c e s s  10 ± 0.7°C in clear weather. The greatest  with  was only difference  between shelter and air temperatures at night under cloudy skies was  similar  to  that  occurring  under  clear  skies  (F=3.22,  df=l,33)  (Appendix IV).  3. Other results  The  type of shelter and the cardinal location of the shelter on the bushes  did not have a significant effect on the maximum Appendix III; and F = 2.21, two  df=2,41, Appendix V  T  e x c e s s  (F=1.65, df=l,45,  respectively). Similarly, these  variables did not have a significant effect on the minimum T  df=2,33, Appendix IV; and F = 0.46,  Radiation  e x c e s s  (F=0.83,  df=2,30, Appendix V I respectively).  (Fig. 14a), shelter  and  air temperatures  (Fig. 14b) and  73  FIGURE 14. Average radiation levels (a), air and shelter temperatures (b), and excess ( ) measured on July 29, 1985 in a high-bush blueberry field in Richmond, B.C. (Bars represent SEM.) T  c  '  11  '  1  13  '  1  15  '  1  17  '  '  1  19  I  21  '  1  23  '  1  '  1  1  3  TIME (HOURS)  ' — I  5  7  '  1  9  •  1  11  75 ^excess (Fig. 14c) obtained on July 29 - a day on which thin clouds appeared and  began to thicken  cloudy  day (Figs.  overnight - were quite  similar to those obtained  10a, 10b, 10c) and a cloudy night  radiation levels during the day were low (maximum jiEm~ s~ ). 2  Although  1  shelter  relatively high compared with the  T  and  was similar to the pattern  e x c e s s  (Figs. 8b and 8c) The  mean value =1079  air temperatures  those under cloudier exhibited  on a  during  ± 179  the day were  skies on Aug. 7 (Fig. 13b), under those cloudy  conditions  (Fig. 13c).  D. DISCUSSION  Temperatures inside the shelter on clear days were higher than air  ambient  and this difference was mainly due to incoming radiation. Solar radiation had  a direct effect on shelter temperature and an indirect effect on air temperature. On a cloudy day with low radiation levels, the shelter temperature did not differ greatly  from  the air temperature  the high  there  radiant  was  input  little  warmed  radiant  heating.  Conversely,  on clear  considerably  higher temperatures. As long as incoming radiation levels were  the  days,  because  the shelter to high,  shelter temperature remained higher than the air temperature. However, as  solar radiation levels fell, the heat the shelters lost to the surrounding air by convection  was not replaced  by radiative  heating, so the shelter  temperature  dropped. As all the irradiated surfaces, including the ground, became cooler in  later  the day, there was less convection, and the air temperature also decreased.  Because shelter  temperatures  started  to fall  earlier  than  the air temperatures,  76 however,  the rate of decrease  the pattern of T did  the  shelter  temperatures that  occurs  the  during in  a  tied leaves. In  air  nights  the  late  shelter  when  a  such instances,  not  of a n y  shelter  body",  absorbs  long-wave  radiation. A t  emissions  cool  the  under  shelter  sufficiently  thick  when  measurements  the  relationships  noted  heating  cooling  and  cloud  and  skies.  do  It  resemble  with  the  air  in  suddenly  radiation  during  to  slightly  expected  that  no  suitable  cloud  have  been  repeated.  those  described  the  shelter by  quickly.  and  it was  clear  expected  shelter, acting  day  values  the  and  re-emits long-wave  than  nocturnal  the  clouds  air, would  the difference between  clouds  temperature,  change and  radiation, the  lower  decrease on  the  air  the shelter  cloudy  conditions. The  there is no incoming  was  very  each other, although cloudy  sun  and  than  and  sudden  the  on  closely  shelter  more  between  the  but  might  between  drop  temperatures  heat and thus  Possibly this,  that of the air; i.e.,  radiation more  passes  air  under  temperature  re-radiate some of the outgoing temperatures.  than  gradual  contrasts  short-wave  night, w h e n  clear  to  steeper  The  significantly different f r o m  a  shelter  was  s  radiative heating, responds  like  and  s  the insolation level drops  the differences would be smaller  particularly  e  thick  that  "black  c  afternoon  differences between  were  x  temperatures.  temperature, i n the absence  The  e  followed that of the incoming  e x c e s s  or  in T  night  of A u g .  occurred In  during  general,  temperature  Wellington  3  (1950)  were the  air not  period  the  diurnal  and  radiant  for  the  air  temperature, the temperature of the different parts of a tree, and radiation.  Some  of  the  temperatures  measured  on  clear  days  seemed  high,  perhaps  77 because of limitations of the available equipment. The thermocouples had to be fine enough to be placed in the shelter without destroying or modifying the shelter characteristics or disturbing the larva. On the other hand, they also had to be strong enough to be manipulated frequently. This problem was tackled by using very fine thermocouple wire inside the shelter and connecting it to a thicker, stronger wire which was then soldered to connectors that could be attached to a switch box. Unfortunately, the junction between the fine and the thick wires could not always be completely shielded from the sun, so that it was sometimes directly exposed to radiant heat. As a consequence, at high radiation levels some of the thermocouples indicated higher than normal temperatures. Since the thermocouples measuring air and shelter temperatures for a given shelter were close together, the same degree of error occurred in both. Therefore, even when both readings were inaccurate, the calculated values  of T  e x c e s s  were  acceptably close to the existing difference.  Larval development of  Cheimophila  is prolonged, lasting almost 5  salicella  months. As for all other poikilotherms, the larvae rely on adequate temperature levels to complete their development. It would therefore be advantageous to exploit the temperature benefits of shelters to accelerate development as much as possible.  Shelter-making  is  a  behaviour  that  exposes  the  occupants  to  temperatures as much as 6° to 7°C warmer than the air in clear weather. Development thus can proceed faster within shelters than outside them, especially when  the  air temperature  is  slightly  lower  than the  larval  developmental  threshold. On such occasions, when skies are cloudless, the temperature in the  78 shelter  would  rise above the threshold  and allow  development to proceed. A n y  mechanism which can promote faster development and pupation before the first frost occurs will aid the survival of this species.  As for  radiation explains  only 4 0 % of T  e x c e s s  , other factors are responsible  the rest of the variation. Air temperature, although indirectly dependent on  radiation,  is another  important  factor, especially  in cloudy  weather.  Anything  affecting the interception and absorption of incident radiation by the shelter also  affect  the magnitude  of T  e x c e s s  . ..Such  variables  include  will  the physical  characteristics of the shelter (colour, size, shape, etc.), its orientation (quadrants) and  location  shelter  with  lighter one,  on the bush a darker  (top, bottom), and its angle  exposed  surface  because it is a better  should  absorb  to the sun's rays. more  radiation  A  than  a  "black body", and thus should be warmer i n  sunlight. This occurred in the mines of the lodgepole needle miner,  Recurvaria  milleri Busk, although the effect of colour was also related to mine size (Henson 1958). In the present study, the colour significantly  the maximum  value  of T  (type) of the shelter e x c e s s  ,  did not modify  but the experiment  was  only  designed to show whether air and shelter temperatures differ from each other, and  consequently did not allow  would  help  for precise  measurements of other factors  in understanding the variation in T  colour, other variables, such as size of the  e x c e s s  that  . To detect any effect of  shelter and its angular orientation to  the sun would have to be held constant. The size and shape of the shelter then have to be considered separately. greater surface  to volume ratio  Henson (1958b) showed that a shelter with a will  become warmer  than one with  a  smaller  79 ratio. The shape of the shelter also will affect its capacity to intercept incoming radiation (e.g., a shelter with a convex surface would be able to intercept some of  the sun's rays  at right angles  "flatter"  shelter would  ^excess  lasting  ^excess ^  The and  or  a  not. Thus  several  hours,  at several a  convex  whereas  times of the day, whereas  shelter could  the flat  shelter  maintain would  a  a  modest  have  a  high  briefer period).  bushes used in this study had few shelters located on the north side  most of those were located  on the upper  part  of the bush. Thus  they  intercepted the sun's rays for a much longer period than any north-facing shelter located lower on the bush. In other words, the insect did not reside (or survive for long) in the less suitable location.  The  side  of the bush  and  therefore  the direction  a  shelter  faces  determines when and for how long radiation will be received. Krenn (1933, cited in and  Geiger 1950) measured temperatures on each side of a tree during found that the side facing east received  radiation for 4.5h from  the day 0700h to  1130h, the side facing south received  radiation for 8.5h from  0830h to 1700h,  the side facing west was heated from  1330h to 1800h (5.5 hours), whereas the  side facing north received no direct radiation from the sun.  The  daily  pattern  of T  e x c e s s  in each of the 4 quadrants studied  here  were somewhat different from each other, as the comparison between the eastand  south-facing  shelters  showed  (Figs.  11  and  12),  with  80 ^excess  reaching  a  higher  value  Nevertheless, i n a high-bush the  overall effect of  amount  of shading  shading  received by  over  time  down  and  the  shelters  in is  blueberry  quadrants  field  may  on  the  such  as  not  be  as  one the  the  shelter varies bushes  thus  grow.  exposing  shade.  as  to the  Consequently,  complicated by  such  the  sun the  changes,  than  on  the one used  the  south.  for this  important  because  of the shelters. The  the sun's  When  east  very  other bushes provide for m a n y  the branches,  remained  earlier  of  are  mature,  and  its  of  the  cardinal  ultimate i m p a c t  is  of  changes  they  weigh  shelters that would otherwise effect  the  amount  position i n the s k y  berries  study,  have  location  of  difficult  to  assess.  After on T  e x c e s s  but  thin  taking  ,  into  partly  construction  cloudy,  weather. In  only  Different  types  some  weather. larvae  by  on  of  shelters  the in  impact of  weather,  half  dark  risk  shelters  of  not  will would  foregoing  factors  bush  might  where  shading  be the " i d e a l "  necessarily  its  be  individuals  provide  one  other  shelter  to year, the species c a n insure  be  in  is  of  the  Dried  the  kinds  among  areas.  temperatures  parts  but  from year  of each generation  example,  exposed  top  all the  shelter would be a relatively large  different locations  l i v i n g i n frequently shaded  in less  the  climate varies  insect to relatively high safer  possible  to radiation is increased. T h a t  spreading  members For  located  relatively cool  fact, as  survival  that  the  one might expect t h a t the " i d e a l "  reduced and exposure in  account  of  a  method  generation. of  well-placed to cope w i t h ideal  for  cool  shelters, w h i c h  i f subjected to intense  weather would  insuring changing or  for  expose  the  radiation, would  of a b u s h and, in fact, are frequently found in  be such  81 places (Chapter II).  High temperatures did not seem to distress the larvae very much. Some of the  days  during  which  this  investigation  was  conducted  hottest of a hot summer. Even on those days, there was  were  among  the  no mass exodus. In  contrast, in Choristoneura conflictana (Wlk.), the larvae drop out of their leafrolls when temperatures reach a overheating by exposed  value of 36°C  C. salicella  was  (Henson  1958b). The  only  sign of  when a larva partially emerged from its fully  shelter during the midday period. It seems that C. salicella  larvae can  withstand high temperatures, at least for a short period of time. More work is needed to understand how  The  shelters  the insect copes with extreme temperatures.  made  of  green  leaves might  also,  through  transpiration,  provide a moister environment than dried leaves, which on occasion could improve the insect's development of Compsolechia the  survival (Bursell  1974b). The  tightly closed leafroll  niveopulvella Chamb., for example, reduces water loss from both  leaves and  (Henson  and  the  1958a). As  ends, its ability  insects  and  increases  the shelter made by  the feeding  rate  of the  occupants  C. salicella is opened slightly at both  to conserve moisture would  not be  so great as  that of  C.  niveopulvella. Shelters made of one dried and one green leaf might be the most versatile, with moisture.  a  dark  surface  for rapid  heating  and  a  live  leaf to provide  82 An should  "ideal"  also  shelter  of  exposed  to the  sun  Shelters  made  of  mortality  Therefore,  there  ^excess  *  not  exist.  is  include are  only  One  maximize  and  well exposed  dried  probably  that  parasites  also  one  increasing  Shelter-making C.  not  m i n i m i z e m o r t a l i t y . A p a r t f r o m exposure  sources  a n (  should  a  and  one  point  at  to observant live  leaf  which  behaviour  "ideal"  on  nevertheless  one  are  Larvae  an  to  development;  could  be an  in  shelters  particularly  "ideal"  be  of  enemies, especially  trade-off occurs  day  seems  rate  it  to lethal temperatures, other  predators.  m o r t a l i t y . Consequently, is  the  adequate  probably  unsuitable adaptation  birds.  conspicuous.  between  shelter  well  the that  does next. allows  salicella larvae to complete their development faster t h a n i f they were entirely  dependent  on  the shelter's  ambient  temperatures.  Without  the  extra  degree-days  provided  by  microclimate, the l a r v a e would not reach the pupal stage before the  temperature i n this locality fell below their developmental threshold.  V. EFFECTS OF THERMOPERIOD ON INSECT DEVELOPMENT  A.  INTRODUCTION  The  thermoperiod, the pattern of temperature  day, is modified for larvae of Cheimophila  fluctuation during the 24h  salicella by the leaf shelters in which  they develop. Consequently, the developmental rate of the larvae is also modified from rates that would occur outside the shelters, perhaps because  the amplitude  of temperature fluctuations is greater inside the shelters than in the ambient air. The  amplitude of daily  temperature  fluctuations can affect the action of some  factors involved i n larval development. larvae of Tribolium  The proteolytic activity in the last-instar  confusum Duv. and T. casteneum (Hbst.) was increased at  temperatures fluctuating between 20°C and 29°C (mean = 24.5°C) compared to the activity  at a constant 28 °C. With  an increase  in proteolytic  activity,  protein  nutrients were better utilized, resulting in an increase in metabolic efficiency and thus ultimately in a decrease in length of development section  presents  C. salicella  the results  of a  in three temperature  laboratory  study  regimes: one with  with moderate fluctuations, and a third  with  (Birks et al. 1962). This of the development large  of  fluctuations, another  a constant temperature. A l l three  regimes had the same daily mean temperature.  The  relationship  development described  as  between  constant  of insects has been extensively an  S-curve  (Wigglesworth, 83  temperatures  and  the  studied. The relationship  1972) with  a  linear  rate  of  has been  middle  section  84 corresponding to the optimal range of temperature for development. outside the optimal range retard the insect's development  Temperatures  and increase mortality.  Insects in the field are subjected to temperatures that fluctuate on a daily and a seasonal basis. Thermoperiods  are analogous  to photoperiods. Each  thermoperiod  consists of a period of high temperature, the thermophase, and a period of lower temperature, the cryophase. Both phases are defined by their duration and their temperature; e.g., a thermoperiod comprising an 8 h cryophase at 10°C and a 16 h thermophase rate  at 25°C can be written, 8C:16T, (10:25°C) (Beck 1983). The  of development  similar, accelerated  of insects  under  alternating  or decreased compared  temperature  to the rate  regimes  may  of development  be  at an  equivalent mean constant temperature.  Survival  and length  of development  of larval  and pupal stages of the  tufted apple bud moth, Platynota idaeusalis (Walker), were similar in alternating and Pieris  constant temperatures in the range 20-33 °C brassicae L. obtained under  expected  under  equivalent mean  (Rock  1985). Growth  alternating temperatures conformed constant temperature  rates of to values  (Neumann and Heimbach  1975). The number of days  from hatching to larval maturity in the European  corn borer, Ostrinia  nubilalis  (Hbn.), was similar under  temperatures  (Beck  1982). And when  were within  the optimal temperature  rate of Trichogramma  the maxima of fluctuating range  for development,  temperatures  the developmental  pretiosum Riley was similar to that at comparable  constant temperatures (Butler and Lopez rate of development  alternating and constant  mean  1980). No differences were found in the  of eggs or nymphs of Lygus hesperus Knight when reared  85 under  fluctuating  temperatures within  the range  15-33°C and  equivalent  mean  constant temperatures (Champlain and Butler 1967).  Other  studies  alternating  have  temperatures  Thermoperiods  produced  shown  that  than  under  shorter  stadia  (Hufn.), than did comparable  insects  the  may  develop  equivalent  for the  black  faster  constant  under  temperatures.  cutworm, Agrotis  ipsilon  constant temperatures (Beck 1986). Exposure of the  aphid parasite, Praon exsoletum (Nees), to fluctuating temperatures resulted in an increase  in the rate  of development  relative  conditions at all mean temperatures below accelerative effect was (Buckton) (Messenger the  24°C  between  and Flitters  significantly  maximum  1958,  and  (6-9%)  under  minimum  1959; Messenger  In  1969). The  regimes  was  10°C,  same  maculata  1964). Development of  Brown, in laboratory studies  alternating  temperature  where the differences were 5 or 15°C result was  (Messenger  under constant  shown for the spotted alfalfa aphid, Therioaphis  red turnip beetle, Entomoscelis americana  accelerated  to that occurring  where but  the  was  difference  not in regimes  (Lamb and Gerber 1985). This laboratory  not supported by field data.  under  alternating  temperatures than under equivalent mean constant temperatures. The  development  of  a  few  cases,  development  has  taken  longer  the Pitcher-plant mosquito, Wyeomyia smithii Coq., at a constant 25°C  was  shorter than under a thermoperiod of 12T:12C, (31.5:18.5°C) lagging the 16L:8D photoperiod by 2 h (Bradshaw  1980).  86 Insects temperature  generally regimes  grow  and develop  in which  at a faster  the minimum  rate  temperature  under falls  alternating below  the  developmental threshold than under comparable mean constant temperatures. Males of Telenomus podisi Ashmead (which could not develop at all) and females (which could develop only marginally) at a constant temperature of 15.5°C successfully developed under  an alternating temperature  regime  of 14:22°C (Yeargan  A t low alternating regimes of 6:20°C and 6:30°C, which had a cryophase the estimated development the tufted  1980). below  threshold of 10°C, developmental rates and survival of  apple bud moth increased relative to the mean temperatures of the  alternating regimes. Thermoperiods  with a cryophase lower than the developmental  threshold tended to produce a lower developmental threshold for A. ipsilon  (Beck  1986).  The  lowered developmental threshold under thermoperiodic conditions can be  explained by the role of limiting factors and accumulated developmental sequences  thermal units. Insects'  involve several rate-limiting factors, particularly enzymes,  whose temperature characteristics may differ. These rate-limiting factors may vary from  one instar  to the next  and from  species to species (Beck  1983).  A  thermoperiodic regime might satisfy all developmental rate-limiting factors, whereas a  relatively  Beck  low constant temperature  might  not (Sharpe  1983). The eggs of Oncopeltus fasciatus  exposed  to high temperatures  (Dallas) for example need to be  (10°C above the hatching threshold) for a few  hours a day in order to complete embryonic development  and DeMichele 1977;  development, even though  can proceed at constant temperatures below  embryonic  the hatching threshold  87 (Lin et al. 1954; Richards and Suanraksa  Yeargan to  (1980) has explained the importance of thermal units in relation  development  developmental  1962).  in thermoperiods  having  threshold. During such  a  cryophase  temperature  thermoperiods, the insect may  below  the  accumulate  more degree-days than it would at the equivalent mean constant temperature. In this situation, the thermoperiod should produce faster development. is based  on  the assumption  that even  occur during the time spent below  though  no  This prediction  significant development  the developmental threshold, neither is there  any adverse effect from repeated exposures to low temperatures (Yeargan  Under  fluctuating temperature  thermophase exceeds reduced mean  survival  and  a  in which  (Yeargan  of development 1980). Larval  retarded and survival was  thermophase exceeded  mean  regimes  the upper  constant temperatures  Praon exsoletum (Messenger  the temperature  limit of the optimal range, insects have  slower rate  constant temperature  apple bud moth was the  the upper  (Rock  may  than  under  development  1980).  of the shown  the equivalent of the  tufted  reduced when the temperature of  limit of 33°C compared to the equivalent 1985).  Similar  findings  were  reported for  1969).  Alternating temperature regimes can also affect fecundity. Although larvae of Wyeomyia smithii took longer to develop under alternating temperatures, adults showed a 7-fold increased in fecundity (Bradshaw the  1980) over those reared under  equivalent constant mean temperature. Siddiqui et al. (1973) reported faster  88 development, earlier attainment of maximum fecundity, and a shorter reproductive period  for the pea  aphid under  fluctuating  temperatures  within  the favourable  range of temperatures, which resulted in a higher intrinsic rate of increase than that found at the equivalent mean constant temperature.  Alternating temperatures can also affect larval and adult weight. Increased larval body weight  (Welbers  1975,  Beck  1986)  and  larger head capsules (Beck  1986) have been reported for some insects under alternating temperature regimes. Adult  red  turnip  temperatures  beetles  than  when  (Lamb and Gerber  1985).  B. MATERIALS AND  Three  16°C, C.  reared  more  under  when  reared  equivalent mean  under  fluctuating  constant  temperature  METHODS  temperature  environmental  weighed  chambers.  regimes  were established in Percival  A l l treatments  had  a  daily  1-35LL controlled  average  temperature  of  as this temperature occurs virtually throughout the whole larval stage of  salicella  (Fig. 15). The  moderate  fluctuating  regime  was  represented by  a  thermoperiod of 8C:16T, (12:18°C) as these minimum and maximum temperatures are commonly found in the field during most of the insect's life cycle and widely  fluctuating  temperature  regime  thermoperiod simulating the greenhouse will be referred to as 16°C, in all growth chambers was  was  represented by  the  18C:6T, (12:28°C), a  effect of the leaf shelters. These regimes  12:18°C and  12:28°C respectively. The photoperiod  16hL:8hD until larvae molted to the 5th instar. At  89  F I G U R E 15. Average minimum and maximum temperatures between April and October at the Richmond Nature Park station of Environment Canada calculated over a 9-year period (1977-1985). The station was located < 1 km from the study site. (Bars represent SD.)  91 this stage of their development, larvae were moved to a HhL:13hD which induced  photoperiod,  pupation.  Fifty-one egg masses were collected from the high-bush blueberry field i n Richmond, B.C.  i n mid-April, 1985  and  randomly  temperature treatments. Each egg mass was  assigned  to one  of the 3  placed in a petri dish with  moist  paper filter and checked daily for hatching. Ten early-hatched larvae were used from each egg mass. As some of the egg masses were not viable, the number of masses in each treatment  varied at the beginning pf the experiment (15 egg  masses at 16°C, 16 in 12:18°C, and 14 in 12:28°C). In a few instances, less than  10 larvae per egg mass were available to start the experiment.  Larvae  were reared  on blueberry  leaves  in 35  7-dram  plastic  snap-cap  vials. The caps of the vials were glued onto an 18.5 x 24.5 cm  sheet of 0.3  cm  of each cap  plastic  through  paneling. A  0.4  the paneling. The  cm  hole  was  drilled  in the middle  panel  was  then  placed over  a  15.5 x 23 x 5  cm  plastic tray filled with water. Freshly cut blueberry stems bearing a few leaves were then inserted through  the holes in the caps into the water. Upon hatching,  larvae were placed individually on each group of leaves and then covered  with a  vial snapped onto the cap. Vial labels were coded so that the development of each individual could be followed separately. The leaves were replaced every 2 to 3 days as necessary.  First  and  second  instar  larvae  were  examined daily  for survival  and  92 moult. Larvae brush was  that had  left the leaves were returned using a fine brush.  disinfected with alcohol and  The  then rinsed in water to reduce the risk  of spreading any viral or bacterial diseases. For the older instars, only the dates at which larvae moulted  to 3rd and  5th instars, or pupated  were recorded. To  reduce the amount of disturbance, older instars were not re-examined  for a  few  days after each moult. Thereafter, they were examined every other day until the size of the head moult  to either  capsule relative to that of the body indicated the  3rd  or  approaching pupation. The  5th  or  until  the  body  impending  changes  indicated  larvae were then examined daily to ensure that their  moulting or pupation date was  The  instar,  an  accurately recorded.  length of development was  obtained in this way  periods: from hatching to the end of the 2nd  for the  following  instar; from the beginning of the  3rd to the end of the 4th instar; and from the beginning of the 5th to the end of the  6th instar. These  "middle"  and  calculated instar.  Sex  "late"  for the was  periods of the larval  instars entire  respectively. The  larval  determined  pre-gonads visible through  the  the skin  hatching to the  absence  (female) or  of late instar  1971). Pupal weights were measured on  termed  length of development  stage, from  by  stage will be  larvae  end  "early", was  also  of the  6th  presence  (male)  (Chapman and  a Metier M E 3 0 microbalance  14  of  Lienk days  after pupation to allow time for the pupae to harden and stabilize their weight.  This  experiment  development and  is  similar  pupal weight  was  to  a  split-plot  analyzed by  design.  The  length  of  analysis of variance (ANOVA)  93 (GLM  procedure, SAS  following larvae  factors: temperature  within  further  Institute 1985) with the variation partitioned between the  egg  partitioned  mass. The into  regime, egg  mass within  variation due  variation  due  temperature  to larvae  to sex  and  regime  of a given egg  that  due  to the  and  mass is interaction  between sex and temperature regime.  The  proportion of dead larvae  at the end  of each period  for each egg mass. Mortality for the entire larval stage was ANOVA  (GLM  Procedure,  SAS  Institute  1985)  was  was  calculated  also calculated. performed  on  An the  arcsine-transformed values of these proportions to determine whether the mortality was  similar  in all temperature  account all larvae of development pupated for  early,  middle  and  Both mortality late  instars  at a  and as  constant  temperature regimes included  12 °C  length of development  well  out by  significance level of 5 %  the developmental threshold  reared  of mortality  in the experiment, whereas in the analysis  of means were carried  Institute 1985). A  As  analysis  and of pupal weight only insects of known sex that  were included.  Comparisons  also  involved  regimes. The  was  as  for the  took  of length successfully  were analyzed  entire  larval  Duncan's multiple-range test  stage. (SAS  used in all analyses.  for C. salicella is not known, larvae  regime  into  to determine  whether  the  were  alternating  temperatures below the developmental threshold.  The  egg masses for this experiment were collected at the same time as those used in  the  16 °C  daily  average  temperature  experiment,  and  the  conditions  were  similar except for the mean temperature of 12 °C. Mortality was  calculated  using  94 the same method as in the 16 °C experiment.  C. RESULTS  1.  Mortality  The  proportion of dead larvae per egg mass for each larval period was  not significantly affected  by the treatments at any stage of their  Most  occurred  of the mortality  mortality  was almost  during the first  2  1 0 0 % (n=150) during the first  instars  development.  (Table  2 instars  II). The  in the 12°C  constant regime (Table II), and only 4 individuals reached the 5th instar.  2.  Developmental  time  a. Early instars  The was  length of development  from  hatching to the end of the 2nd instar  significantly different in different temperature  regimes  (F= 16.39, df=2,40)  and between egg masses within a given temperature regime (F=1.67, df=40,122) (Appendix IX). Insects reared in the 12:28°C regime developed significantly faster than those reared in the other 2 regimes  (Table III). Insects i n the 12:18°C  regime took the longest to reach the 3rd instar. About 2 5 % of the larval stage was spent as early instars.  95 TABLE II. Mortality for each larval period of Cheimophila salicella reared at daily average temperatures of 12° and 16 °C.  LARVAL PERIOD  #DEAD / INITIAL # OF LARVAE  12°C  16°C  1ST AND 2ND INSTARS  138/150  181/441  3RD AND 4TH INSTARS  8/150  32/441  5TH AND 6TH INSTARS  4/150  45/441  150/150  258/441  1ST TO 6TH INSTAR  TABLE  III.  regimes  Time n q u l r a d  having  a dally  by  Che ImophlI  average  a salicella  temperature of  TEMPERATURE  DAYS REQUIRED  REGIME  —  —  1ST  —  CONSTANT  to complete  each  larval  period  In three  temperature  TO COMPLETE THE  FOLLOWING  PERIODS OF  LARVAL  DEVELOPMENT  •  AND  2ND  3RD A NO  INSTARS'  16'C  larvae  1C*C.  4TH  INSTARS  5TH A NO STH  1ST  TO END OF  INSTARS  STH  INSTAR  24.5 ±  0.3 a  26.2  ± 0.4 a  44.2 1  0.9 a  95.4  ± 0.8  a  8C:16T.  (12:18*C)  26.1 ±  0.3 b  27.5  ± 0.6 b  51.2 ±  1.3 b  104.5  ±  1.1 b  18C:6T.  (12:28*C)  23.1 ±  0.4 c  19.5  ± 0.3 c  54.5 ±  0.9 c  97.4  1  1 .O a  Means  w i t h i n columns  test.  P<0.05. SAS  not followed  Institute  1985)  by  t h e same l e t t e r  are s i g n i f i c a n t l y d i f f e r e n t  (Duncan's n u l 1 1 p l e - r e n g a  97 b. Middle  instars  The the  length of development  4th instar  (F= 131.94,  was  df=2,39)  from the beginning of the 3rd to the end of  significantly (Appendix  different  X). Insects  developed from 3rd to 5th instar on average  among reared  the temperature in the  regimes  12:28°C  regime  7-8 days (almost 33%) faster than  larvae held in the other temperature regimes (Table III). Insects in the 12:18°C temperature regimes took significantly longer to complete their development  than  did those in either 16°C or 12:28 °C.  Females This  difference  developed was  faster  than  not confirmed  males by  non-adjusted means but a comparison required only 24 + required 25 ± 27%  (F=7.54, df= 1.110) (Appendix X).  Duncan's  multiple  of adjusted means  range  test  on the  showed  that  females  0.4 days to develop from 3rd- to 5th-instar, whereas males  0.4 days. The amount of time spent as middle instars was about  of the larval  stage for insects reared in the 16°C and 12:18°C  regimes  (roughly the same as for the first 2 instars). However, insects reared in the 12:28°C regime  spent slightly  less  that  2 0 % of their  larval  stage as middle  instars.  c. Late instars  The  length of development  different temperature  regimes  of late instars differed significantly among the  (F=36.30, df=2,40) (Appendix  XI). Larvae reared  98 in the 16 °C the  regime  12:18°C regime  on  average  also  a  males (46 ±  longer than larvae  difference  required  the other regimes. There  SEM) and females (54 ±  was  XI) in the time 0.9 days) required  development.  all treatments, the period extending from the beginning of the 5th to  end of the 6th instar  reared  from  (F = 51.26, df= 1,111) (Appendix  0.8 days) (mean ±  to complete their  the  (Table III). Larvae reared in the 12:28°C regime  3-10 days  significant  In  reached the pupal stage first, followed by those reared in  was  in the 12:28°C regime  the longest of all groups spent 5 6 % of their  of instars.  larval development  instars, whereas those in the 12:18°C and 16°C regimes  Larvae as late  spent 4 6 % and 4 9 %  respectively.  d.  1st-  to end  There larvae Larvae  of  6th-instar  was  in different  a significant difference i n the length of development temperature  reared in the 12:18°C  regimes regime  (F=20.96, took  df=2,41)  on average  6-8  of the  (Appendix XII). days  longer to  develop from the 1st instar to pupae than those in the other 2 regimes (Table III). Females took significantly longer than males to go through their larval stage (F=29.92, df= 1,123), requiring 95  ±  0.8 days.  on average  103 ±  0.8 days, whereas males took  99 3.  Pupal  weight  There  was  a  temperature regimes  significant  difference  in pupal  weight  in the different  (F=6.16, df=2,41) and between larvae from the same egg  mass (F=1.65, df 41,124) (Appendix XIII). As a consequence, pupal  weight  between  insects  from  different  regimes  the difference in  must be  caution. Pupae of larvae reared in the 12:28°C regime weighed  examined  on average more  than those reared in the other temperature regimes (Table IV). There a  with  was also  significant difference in pupal weights between males and females (F=62.41,  df= 1,124) (Appendix 30.2  ±  XIII).  Females  weighed  42.9  ±  1.28  mg  and  males  0.63 mg.  D. DISCUSSION  1.  Mortality  As  Cheimophila  salicella  is exposed  to temperatures in the field ranging  from less than 12 °C to more than 28°C, it is not surprising that the different temperature youngest  regimes  larvae  used  here  did not significantly  affect mortality. Even the  survived  quite  well  temperature  under  a  daily  fluctuation of  16°C, an amplitude which is much greater than the air temperature fluctuations in  the field  development. fluctuations  during  the period  in which  Since  larvae  leaf  than  those  found  in  larvae  shelters  in the outside  are in this  experience air, they  stage  wider  could  be  of their  temperature expected to  100 T A B L E IV. Weigths of 14 day-old Cheimophila salicella pupae from larvae reared in three temperature regimes having a daily average temperature of 16 °C.  TEMPERATURE  REGIME  P U P A L W E I G H T (mg) MEAN  16 °C  CONSTANT  ±  SEM  1  33.9  ±  1.37 a  8C:16T, 12:18°C  35.9  ±  1.48 a  18C:6T, 12:28°C  40.0  ±  1.55 b  Means not followed by the same letter are significantly different (Duncan's multiple-range test, P<0.05, S A S Institute 1985).  101 tolerate them as well as they did here.  Most (39.8%) larval mortality occurred  during early instars and was due  in part to high humidity inside the vials.  The  1st- and 2nd-instar  become trapped  in condensation  larvae tended  instars,  mesh. This which  design  sometimes  the leaves and  that accumulated on the sides of the vials. To  decrease the humiditj', the plastic bottom cotton  to disperse from  was satisfactory chewed  holes  of the vials was replaced for small  through  the stem  effectively  blocked  the mesh  and escaped.  that escape route, although  occasionally found an opening near the stem to crawl  fine  larvae but not for later  larvae also escaped through the hole drilled i n the vial cap. Wrapping around  with  Some  "Play-doh"  a few larvae  through.  Some mortality also was caused by handling. Although used to manipulate larvae, a few were injured when leaves  a soft brush was were changed or  when wanderers were put back on their leaves. Since early instars had to be checked daily for moulting, this disturbance also contributed to their mortality.  The  mortality sustained  i n the 12 °C  constant  regime was much greater  than that i n the daily average temperature of 16°C. The condensation was  more severe  problem  at 12 °C, but does not explain such an increase i n mortality.  Indeed, the high mortality at 12 °C  indicates that this temperature is not within  range for Cheimophila  salicella's development. Insects have different  the  optimal  102 developmental thresholds for different stages of their development Beck  (Bursell 1974b;  1983). A variety of thresholds (developmental threshold, hatching threshold,  developmental-hatching determined A l Rawy  threshold,  hatching-survival  for various insects  (Johnson  threshold,  etc.) have  been  1940; L i n et al. 1954; Hodson and  1958; Richards 1959). The eggs of the hemipteron, Oncopeltus fasciatus  (Dallas), require 13°C for only hatching to occur, but require 15°C for hatching and full development young  bugs  and over 17°C for development  (Richards  1959).  The eggs  and the production of viable  of C. salicella  used  in the 12°C  temperature regime had been in the field for up to one month before they were brought to the lab. Diurnal fluctuation of temperatures i n the field might provided  the eggs  development  with  temperatures  that  met the requirement  to be completed. In the lab, the 12 °C  have  for embryonic  constant regime might have  been sufficient for the eggs to hatch. However, had the eggs been placed at 12°C immediately following oviposition, i t is probable that have occurred. In other words, 12 °C threshold of Cheimophila  hatching would not  is probably lower than the developmental  salicella.  2. Effect of temperature regimes on larval development  Using the 2 criteria of length of time required for development weight  as an indicator of fitness, larvae did best under  12:28°C temperature regime. There between  the widely fluctuating  regime, and second-best in the 16°C constant temperature  was no significant difference i n the length of larval  individuals  and pupal  i n 12:28°C  and those  i n 16°C. More  development  importantly, the  103 individuals in the 12:28°C regime produced significantly heavier pupae than those from the 16°C constant regime. The 12:18°C temperature regime did not provide any  advantage  for larval  slower in the 12:18°C  development.  regime  Overall, larvae  developed significantly  than in the others and the pupae were not  significantly heavier than those produced in the 16°C constant temperature.  In  many cases of faster insect development  in fluctuating vs constant  temperature regimes, the acceleration in development is due to an accumulation of extra thermal units in the fluctuating regime (Yeargan 1980). These extra thermal units are accumulated only when the following conditions are met: 1) the average daily temperature is similar in both constant and fluctuating regimes; 2) the temperature  of the cryophase  is below the developmental threshold.  Mathematically, thermal units available to insects in a 24h period are calculated as follows: n  L (Tj - a) X H , where Ti  i= 1  Tj = value of the ith temperature (°C) to which the insects are subjected in a 24h period; a = developmental threshold; H-p; = amount of time (h) the insects are subjected to Tj. In cases when Tj is lower than a, the value of Tj - a is set at 0. If the developmental threshold was <12°C, the thermal units accumulated by the larvae under each temperature regime in 24h would be:  104  16°C:  (16°-12°C) x 24h = 96 D H  (degree hours),  1  12:18°C:  (12°-12°C) x 8h + (18°-12°C) x 16h =  96 DH,  12:28°C:  (12°-12°C) x 18h +  96 DH,  (28°-12°C) x 6h =  In this instance, the same number of thermal units is being accumulated every day in each of the temperature regimes.  In this study, extra thermal units could be accumulated only i f 12 °C was below the developmental threshold and, as previously discussed, that is probably the case. If the developmental threshold were above 12°C, e.g., 13°C, then the thermal units accumulated in a day for each temperature regime would be: 16°C:  (16°-13°C) x 24h =  72 DH,  12:18°C:  (12°-13°C) x 8h + (18°-13°C) x 16h =  80 DH,  12:28°C:  (12°-13°C) x 18h + (28°-13°C) x 6h =  90 DH.  In  these circumstances, the thermal  Whatever would  the developmental threshold  units (13°C,  accumulated  in each  regime  14°C, etc.), the 12:28°C  vary. regime  always accumulate more thermal units in 24h than the 12:18°C regime,  and  the latter in turn would  always  accumulate  more than the 16°C regime.  The  net result of these differences is that larvae subjected to 12:28°C should  develop faster than those at 12:18°C, which in turn should develop faster than larvae reared at 16°C. The latter difference did not occur in this  experiment  (Table III). Larval development of insects subjected to the 12:18°C regime was slower than those in the 12:28°C and 16°C regimes. The significant increase in ' t o convert the amount of thermal units from D H the number of D H by 24h/day.  to DD  (degree days), divide  105 developmental time for larvae in the 12:18°C regime is probably attributable to the length of the thermophase (16 hours) a length not encountered in the field in spring or fall. Cook (1927), Peairs (1927) and the  highest  rate  of  acceleration  in  insect  Huffaker (1944) reported that development  under  alternating  temperatures is obtained when the thermophase is 6-8 hours.  Higher  temperatures  in the  fluctuating  temperature  deter pupation in the last stage of larval development.  regimes  appeared  to  Larvae subjected to the  highest daily temperatures took longest to pupate whereas those at 16°C  pupated  fastest.  by  A  maximum  fluctuating  regimes  development the  field  was  daily  temperature  probably  lower  required  than  during the  that  provided  latter  stages  of  the larval  to trigger pupation. This is understandable, as air temperatures in  in early  October  rarely, if ever, reach levels near  28°C. With  the  autumn mid-day sun at lower angles, temperatures in the leaf shelter would also usually be cooler than 28°C.  Among the 3 temperature regime  was  developed accelerated  the  most rate  most rapidly  beneficial through  enabled larvae  regimes  tested in the laboratory, the 12:28°C  for C.  salicella.  the  first  to spend  part  In of  less time  this  regime,  their  larval  in their  early  the  larvae  stage. This instars  and  thus, in natural situations, would reduce larval mortality from predation. Most of the  body  weight  was  gained  during the  late  instars,  since  the  late  instars  occupied the bulk of the larval stage, both in the laboratory (Table III) and in the field (Fig 7).  106  3. Importance of the shelter on larval development  The shown  importance  by comparing  of the shelter on larval development of C. salicella is best the extra number  of degree-days  (DD) provided  by  the  shelter and the total number of DD required by the insect to complete its larval development.  The 286  number of DD required for larval development can be estimated at  DD (from Table III and using a developmental  threshold of 13 °C).  Similarly,  the number of extra DD provided by the shelter can be estimated  using the  following  assumptions:  1- Developmental threshold is 13°C; 2- Thermal advantage of leaf and flower buds is similar to that of leaf shelters; 3- On cloudy or partially sunny days, the extra heat (T  provided by the shelter  ) has a value of 0 C ; 6  e x c e s s  4- On sunny days, T and  August  ^excess May  a n  ^  e x c e s s  has a value of 6°C and lasts 5h. Between June 1  31, air temperature a  n  t n e  e x  tra  heat  is available  and Sept., air temperature  period of high T  e x c e s s  is above  13 °C  during the period of high  for larval  is sometimes lower  and it is estimated  development. than  During  13°C during the  that the extra heat provided by  the shelter contributes only 3°C above the threshold.  In  1985, a total of 94 extra DD  were provided  shelter during the larval stage of C. salicella.  C. salicella  to the larva by  the  requires 286 DD to  107 complete its larval development, from hatching in May to pupation in October, when only 192 DD are available from air temperature alone. Without the effect of the shelter, the larvae would not develop beyond the 5th instar before frost occurred. The 94 DD provided by the shelter enables the larvae to be pupae and survive frost. Therefore the shelter is of critical value to C. salicella survival in the climate under study.  for  VI.  The  shelters  microclimate  warmer  C.  larvae  salicella  warmer of  made than  development,  complete  their  temperatures. pupate  mainly  l a r v a l stage  relatively  larvae  salicella  provide  a i r on clear days.  on temperature  the insect  microclimate earlier  than  i f they  is p a r t i c u l a r l y i m p o r t a n t late  i n the fall,  even  were  development.  Because  allows  subjected  for the l a r v a e  with  the help  a  such as  for their  of the shelters  with  Poikilotherms  w i t h i n the optimal range for development increase  the w a r m e r  This  C.  the ambient  rely  temperatures  by  CONCLUSION  the rates  the insects to only  to ambient  of C. salicella, of the higher  which shelter  temperatures.  The  effect of the w a r m e r  microclimate of the shelter  important for the insect on clear a n d cold s p r i n g temperature then  provide  prohibits  development.  the larvae  T h e shelter,  w i t h temperatures  days w h e n through  high  m a y be p a r t i c u l a r l y the low ambient a i r  radiative  enough to allow  heating,  would  development to  proceed.  Solar difference  radiation  between  is  shelter  modify  the interception  shelter  need  microclimate species  to in  to s u r v i v e  one of and  the more  air  temperatures.  and absorption  be  studied  which  C.  if  we  salicella  important  of incoming are  lives,  to  b u t also  i n a n uncertain environment.  108  better  variables  Several solar  affecting the  factors radiation  understand the " t a c t i c s "  Some of these  that  might  by the leaf  not only  the  used  this  by  factors include the  109 orientation  of the shelter  to the sun, its cardinal  position  on the bush, the  amount of shading it receives, and its colour, shape, and size.  First- to fourth-instar regime  than  instars,  under  however,  larvae developed faster under the widely fluctuating  the moderately required  longer  fluctuating to reach  or the constant regimes. the pupal  fluctuating regime than in any other, probably because  stage  Later  in the widely  the high temperature of  the thermophase interfered with their pupation processes. This slower development, on the other hand, allowed the larvae to produce heavier pupae. Overall, larvae in the widely fluctuating and i n the constant regimes did not take a significantly different amount of time to develop from long  thermophase  development  of the  moderately  1st instar to pupa. It seems that the fluctuating  regime  retarded  the  larval  of C. salicella.  The developmental threshold of C. salicella was unknown at the time this study was undertaken. Since an accumulation of extra thermal units is the most likely  explanation for faster  development  i n the widely fluctuating  temperature  regime, this threshold is probably above 12 °C. The effects of the amplitude of temperature fluctuation on development, effects  of extra  degree-days  if any, cannot be distinguished from the  present in the fluctuating  regimes. Although  this  experiment did not establish the effect of the amplitude of temperature fluctuation on  development,  it nevertheless  provided  developmental threshold of C. salicella  useful  information  regarding the  and confirmed the field observation that  larvae subjected to a greater number of degree-days develop faster. Furthermore,  110 without would  the not  leaf-tying C.  salicella  extra be  able  behaviour  degree-days to  pupate  thus  provided  by  the  shelters,  before  the  first  lethal  contributes  substantially  and is critical for its s u r v i v a l i n southern  larvae frost  to B.C.  larval  in  of the  C.  salicella fall.  development  The of  LITERATURE  CITED  Andrewartha, H.G., and L.C. Birch. 1954. The distribution animals. Univ. of Chicago Press, Chicago, 111. 782 pp.  and abundance of  Barbosa, P., M.G. Waldvogel, and N.L. Breisch. 1983. Temperature modification by bags of the bagworm Thyridopteryx ephemeraeformi (Lepidoptera: Psychidae). Can. Ent. 115(7): 855-858. Beck, S.D. 1982. Thermoperiodic cornborer,  Ostrinia  nubilalis.  induction J.  of larval  Insect Physiol.  . 1983. Insect Thermoperiodism.  Annu.  diapause  i n the European  28: 273-277.  Rev. Ent. 28: 91-108.  . 1986. Effects of photoperiod and thermoperiod on growth ips.ilon (Lepidoptera: Noctuidae). 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Effects of temperature on development rate of Telenomus podisi (Hymenoptera: Scelionidae). Ann. ent. Soc. Am. 73: 339-342.  APPENDIX I  Correlation  analysis  between  T  e x c e s s  (difference  between  air and  shelter  temperatures) and levels of incoming solar radiation recorded for the leaf shelters under sunny conditions in a high-bush blueberry field in Richmond, B.C. in 1985.  SOURCE OF VARIATION  df  SS  1  4773.99  ERROR  563  6700.61  TOTAL  564  11474.59  RADIATION  ***, P<0.0001.  118  F  401.12 ***  0.415  APPENDIX II  Correlation  analysis  between  T  e x c e s s  (difference  between  air  and  shelter  temperatures) and levels of incoming solar radiation recorded for the leaf shelters under cloudy conditions in a high-bush blueberry field in Richmond, B.C. in 1985.  SOURCE OF VARIATION  RADIATION  ERROR  TOTAL  •  df  SS  1  230.52  129  492.13  130  722.64  ***, P<0.0001.  119  F  60.43 ***  0.310  A P P E N D I X III  Analysis of variance of daily maximum T  e x c e s s  (difference between  air and  shelter temperatures) under different weather conditions (sunny, cloudy) between Aug. 3 and Aug. 17, 1985 in a high-bush blueberry field in Richmond, B.C.  SOURCE OF VARIATION  df  SS  WEATHER CONDITIONS  1  241.87  ERROR  49  731.36  TOTAL  50  973.23  **, P<0.0005.  120  F  16.20 **  A P P E N D I X  I V  Analysis of variance of the length of development of male and female early instar Cheimophila salicella larvae reared in 3 temperature regimes.  SOURCE OF VARIATION  df  TEMPERATURE REGIME  SS  F  261.93  16.39  319.63  1.67  *  0.59  0.12  ns  24.23  2.53  ns  ***  EGG MASS WITHIN TEMPERATURE REGIME  40  SEX  TEMPERATURE X SEX  ERROR  122  584.50  TOTAL  167  1191.79  ***, P<0.0001; *, P<0.05. 121  APPENDIX V  Analysis of variance of the length of development of male and female middle instar Cheimophila salicella larvae reared in 3 temperature regimes.  SOURCE OF VARIATION  df  SS  F  TEMPERATURE REGIME  2  2044.60  131.94  39  302.17  0.70  ns  7.54  *  EGG  ***  MASS WITHIN  TEMPERATURE REGIME  SEX  1  TEMPERATURE X SEX  2  83.91  4.46  ERROR  110  1223.86  TOTAL  154  3607.42  ***, P<0.0001; *, P<0.05.  122  0.20 ns  APPENDIX  VI  Analysis of variance of the length of development of male and female late instar Cheimophila  salicella  larvae reared in 3 temperature regimes.  SOURCE OF VARIATION  df  SS  F  TEMPERATURE REGIME  2  3013.85  36.30  40  1660.72  1.18 ns  SEX  1  1803.29  51.26 ***  TEMPERATURE X SEX  2  162.19  2.31 ns  ERROR  111  3904.78  TOTAL  156  11432.33  ***  EGG MASS WITHIN TEMPERATURE REGIME  P<0.0001. 123  APPENDIX VII  Analysis  of  variance  Cheimophila salicella  of  the  length  of  development  of  male  and female  larvae reared in 3 temperature regimes.  SOURCE OF VARIATION  df  SS  F  TEMPERATURE REGIME  2  2246.16  20.96  41  2196.47  1.36  SEX  1  1174.72  29.92  ***  TEMPERATURE X SEX  2  56.70  0.72  ns  ERROR  123  4829.36  TOTAL  169  11743.51  ***  EGG MASS WITHIN  TEMPERATURE REGIME  ***, P<0.0001. 124  ns  APPENDIX VIII  Analysis Cheimophila  of  variance salicella  of  the  weight  of  14  day-old  male  and  pupae from larvae reared in 3 temperature regimes.  SOURCE OF VARIATION  df  SS  TEMPERATURE REGIME  1433.33  6.16  4767.31  1.65  4406.75  62.41  EGG MASS WITHIN TEMPERATURE REGIME  41  SEX  TEMPERATURE X SEX  149.17  ERROR  124  8756.13  TOTAL  170  21933.13  ***, P<0.0001; **, P<0.005; *, P<0.05. 125  1.06 ns  female  


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