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Design of a sampling system for the larch casebearer Coleophora laricella Hbn Moody, Benjamin H. 1977

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DESIGN OF A SAMPLING SYSTEM FOR THE LARCH CASEBEARER (Coleophora l a r i c e l l a Hbn.)  by  Benjamin H. Moody  B. Sc. F., University of New Brunswick,  1968  . M. Sc. F., University of New Brunswick,  1971  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY  in  THE FACULTY OF FORESTRY We accept this thesis as conforming to the required  THE UNIVERSITY OF BRITISH COLUMBIA January,  1977  Benjamin H. Moody,  1977  standard  In presenting this thesis in partial  fulfilment of the requirements for  an advanced degree at the University of B r i t i s h 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 representatives.  It  is understood that copying or publication  of this thesis for financial gain shall not be allowed without my written permission.  Department of  f oYgyf< \^  The University of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5  ABSTRACT  The problems that a r i s e in developing a sampling design for the  various l i f e stages of the larch casebearer, Coleophora  laricella  (Hbn), are treated in relation to the changes in population density and d i s t r i b u t i o n throughout the l i f e cycle of the insect.  The basic  principles of population sampling are followed in respect to s t r a t i f i c a t i o n of  the sampling universe into i t s logical components.  successive samplings are s a t i s f i e d .  Replications and  The p e c u l i a r i t i e s of branch  structure, with short shoots, long shoots and f a s c i c l e s of needles provide c r i t e r i a for the ultimate sampling units. with relation to: 'open grown  1  Sampling was conducted  position of trees in the stand ( i n t e r i o r , edge, or  trees); d i f f e r e n t crown levels; d i f f e r e n t branches at the  same level based on exposure to sky-light; d i f f e r e n t 6-inch  (15cm)  segments of a branch throughout i t s length and d i f f e r e n t stages in the i n s e c t s 1i fe eyele. 1  The main purpose of this investigation was to test the hypothesis that s h i f t s in population concentrations influence the accuracy of sampling at fixed points in the crown of a tree. of  If this be so, refinement  techniques may become possible. Of the theoretical d i s t r i b u t i o n s tested the negative binomial  gave the best f i t to the data for a l l l i f e stages except the egg stage which approached the  the normal d i s t r i b u t i o n .  needle f a s c i c l e and the 15~cm  similar s t a t i s t i c a l  distributions.  Analyses of two sample units,  branch section respectively, revealed  The variance of the number of insects per needle f a s c i c l e calculated for each tree sampled was  highly related to the mean.  Therefore, approximate normality of the data was achieved by application of Taylor's power transformation, but with the modification of adding a "C" constant to the variable before raising the equation:  i t to the power of P,in  Y. = (X. + C)'", where Y. = transformed observation, i I I >  X. = original observation, C = 1 and p = (1 derived by the method of least  1/2b) where b^ is a constant  squares.  The analyses of variance showed that tree-to-tree, v e r t i c a l and horizontal position of the samples in the tree crown were the most consistent variables influencing the d i s t r i b u t i o n of eggs, larvae and pupae, while exposure of the tree in the stand had l i t t l e e f f e c t .  The  d i s t r i b u t i o n s of eggs with relation to the quantity of needles, type of shoots, and condition of needles (oviposit ion sites) on the branch were examined.  The determinant factors in insect d i s t r i b u t i o n s were also  recogn i zed. A practical three-stage sampling design was developed  by  considering variations between trees, and v e r t i c a l and horizontal within the tree crown.  strata  The f i r s t stage is concerned with selection of  the tree(s), the second stage would be the crown level within a tree, and the third stage the branches within each crown l e v e l .  The variable  to be estimated should be the number of insects per needle f a s c i c l e or short shoots (spurs) in winter.  Such a sampling design would provide  estimates of population trend and mortality within a generation.  - ii -  TABLE OF CONTENTS  D  Page ABSTRACT . .  i  TABLE OF CONTENTS  i i i  LIST OF TABLES  viii  LIST OF FIGURES  xi  LIST OF APPENDI CES  xiii  ACKNOWLEDGMENTS  xv  INTRODUCTION  1  Earl ier Work  4  Deficiencies of Former Methods  7  THE INSECT  10  Taxonomy  10  World Distribution  12  Significance as a Defoliator  14  Biological Characteristics of the Insect  16  Morphological  17  Forms and Stages  L i f e History  19  Reproduction, Growth S Morphogenesis  19  THE HOST TREE  22  Host species and S u s c e p t i b i l i t y  22  The Host Tree in B r i t i s h Columbia  24  The Host Tree as a Sampling Unit  27  Morphological Characteristics of Larch  28  Deciduous Characteristics of Larch  30  Vegetative Cycle  30 - iii -  THE STUDY AREA, MATERIALS AND METHODS  31  Need for Choosing Sampling Area  31  Sampling Procedures  34  The Sampling Universe  35  Selection of the Sampling Unit  35  Timing of Sampling  36  Field Procedures  40  Assessing the Tree  45  Sampling for Morphological Characteristics of Branches  45  Distribution of Fol iage and Shoots  45  Defoliation Measurements  46  Rating Defoliation  4  Insect Counts and Accessory Information  6  47  Overwintering Larval Samples . .'  ^  Checking Insect Counts  49  Rearing Methods  50  Experimental Observations  50  ANALYSIS OF DATA  5  2  F i t t i n g the Distributions  53  Transformations  54  Taylor's Power Law  . . . . . . .  55  Analysis of Variance or '' F '—Test  57  Regression and Correlation  58  The Number of Samples  6  0  63 Allocation of Optimum Sampling Effort Data Preparation and Analysis Procedures The Basic Unit of Sampling  .  63 63  - iv -  RESULTS AND  DISCUSSION  65  Frequency Distributions  65  The  69  Variance - Mean Ratio  'k' as an  Index of Aggregation  69  Discussion on Distribution  74  Transformation of Data  76  FACTORS AFFECTING THE Source of Variation  79  in Population Estimate.  79  Inter-Tree Variation  79  Intra-Tree Variation  80  1.  Crown Level Variation  80  2.  Exposed and  81  3.  Main or Side Branches  87  k.  Horizontal  87  DISTRIBUTION OF THE The  DISTRIBUTION OF CASEBEARER  Egg  Shaded Branches .  Crown Position POPULATION BY LIFE STAGES  Stage  89  .  89  Distribution of Eggs  89  Current Growth vs. Adventitious Foliage vs.Old Growth Foliage.89 Egg  Placement on the Needle Surface  91  Vertical Distribution of Eggs  93  Horizontal  .93  Distribution of Eggs  Relationship Egg Egg  Between Degrees of Defoliation and  per Fascicle  Number of 95  Distribution in Relation  - v -  to Adult Behaviour  98  The  Larval Stage  100  Larvae Prior to Winter Dormancy  100  Spring or Postwinter Larvae  101  Larval Variation Between Trees  101  Vertical Variation in the Tree Crown  101  Exposure  104  Main and Side Branches  106  Horizontal  106  Crown Variation  Comparison of Branch and Branch Tip Samples  107  D i scuss ion  108  Reasons Underlying the Distribution of Larvae  109  Larval Behaviour and Distribution Effects The Pupal Stage  HO 1  1  4  Vertical Distribution Horizontal  Crown Position  H4  Exposure  H6  Factors Affecting Pupal Distribution  H6  Larch Fol iage Distribution of Larch Fol iage in the Crown Fascicles 1.  Tree-to-Tree Variation  2.  Crown Level Variation  1  3.  Exposure  I  2  4  k.  Main and Side Branches  I  2  4  5. Horizontal  Crown Position  - vi-  2  2  ]Zk  Other Factors of Foliage Affecting  Insect D i s t r i b u t i o n . • • . 127  Number of Needles per Fascicle  128  Needle Length and Fascicle Weight.  129  Intra-branch Variation  130  in Fascicle Size  Inter- and Intra-tree Variation  130  Discussion on Needle Fascicles  131  I nsect Mortal i ty  132  Insect Mortality and Effects on Distribution  132  Spatial Difference  135  in Mortality  Vertical Distribution of Mortality Horizontal  Distribution of Mortality  Seasonal Fluctuation  135 in the Crown- . . . . . . .135  in Casebearer Population  Recommendations for Sampling-  136 139  The Egg Stage  139  The Larval  140  Stage  Pupa  141  A General Sampling Design  142  Sample S ize  144  SUMMARY AND CONCLUSIONS  148  LITERATURE CITED  153  APPENDICES  159  - vii-  LIST OF TABLES Table  Page  1  Frequency d i s t r i b u t i o n s of numbers of insects (larch casebearer) per f a s c i c l e for the l i f e stages sampled . . . 66  2  Effect of development of larch casebearer during a single generation on estimate of the parameter k_and b^ for i t s immature stages, Thrums, B.C.  3 4  197^"75  Estimates of k_ of the negative binomial for each stage per f a s c i c l e and per 15-cm branch section  insect 72  Regression and correlation of log variance on log mean for a l l stages of the larch casebearer  5  73  The correlation between mean and variance for the l i f e stage of larch casebearer  6  71  77  Egg d i s t r i b u t i o n by needle condition  and on needle  surface - 1974  91  7  Distribution of eggs on the needle (197*0  92  8  Distribution of C. l a r i c e ! l a egg per f a s c i c l e by crown levels as collected at Thrums 197^ and 1975  9^  9 10  11  Distribution of C_. lar ice! la eggs per 15 cm branch section by crown levels and years  3k  Number of larch casebearer by tree branch type and horizontal crown position per f a s c i c l e per 2-15 cm branch sections  96  _  Defoliation rating by tree, crown level and exposure at time of egg stage,  12  96  197*t  Moth a c t i v i t y as observed on 14-15 June 197^ at Thrums, B.C.  13  99  Average number of larvae per f a s c i c l e and per 15 cm branch section by tree and stand position _  102  14  Avg.No.of casebearers/15 cm branch section collected 197^-103  15  Number of larvae per f a s c i c l e by casebearer stage, exposure and crown levels  16  104  Avg.No.of larvae per f a s c i c l e for 12 trees at Thrums by horizontal  crown position - viii -  . . .  107  17  Comparison of spring larvae per f a s c i c l e by branch 108  18  tips and by the outer third of branch . . . . . The number and percentage of normal and needle t i p cases by tree for the prewinter larvae 197**  110  19  Densities of pupae by crown levels in ~lk and '75  20  Densities of pupae by horizontal crown position  21  Avg.No.of pupae per f a s c i c l e by year, position of trees  ....  l  115  jn',7^ &'75.115  in the stand and exposure  117  22  Analyses of variance of numbers of f a s c i c l e s per  23a  I5~cm branch section Analyses of variance of numbers of f a s c i c l e s per 15~cm branch section collected for egg counts in 197^ and  119  1975  23b  Analyses of variance of f a s c i c l e s per  I5~cm  120  branch  section from samples collected for larva^ and larva^. . . 121 2k  Density & percentage d i s t r i b u t i o n of needle fascicles/15 cm branch in 3 crown levels of western larch at Thrums,B.C.. 122  25  Number of f a s c i c l e s and eggs per 15~cm  _  branch section  by year and crown level 26  27  123  Average number of f a s c i c l e s per 15 cm branch section by c o l l e c t i o n period, crown level, exposure and branch type -  Average number of f a s c i c l e s and eggs per  125  15cm _  branch section by year, exposure and branch type 28  Distribution of insects and appropriate f a s c i c l e s per 15~cm  29  126  branch section by horizontal crown position. .  .127  Average number of needles per f a s c i c l e by tree and crown levels  30  128  Avg.needle length (cm)  for samples taken from  h trees in 1975 31  Avg. weight of f a s c i c l e as calculated with the use of Ives  0955) 32  129  formula, for an:interior(1) and an  edge(6)  tree. .  .130  Survival of C_. l a r i c e l la through one complete generation near Thrums, B.C.  - ix -  197^-1975  13* 1  33  Number of postwinter larvae and desiccated l e v e l , 1975. . . . . . .  larvae by crown  134  34  Average number of pupae, adults and parasites per f a s c i c l e by crown l e v e l , 1975 137  35  Average number of pupae, adults, parasites per f a s c i c l e by exposure and branch type, 1975 •  36  Average number of pupae, adults and parasites per f a s c i c l e by horizontal crown position, 1975  137  37  Analysis of variance f o r three-stage  38  The calculated required number of trees to be sampled by insect stage and sampling precision Mean (x) and standard error of the mean (S—) f o r the various l i f e stages sampled in numbers of insects per fascicle  39  137  - x -  sampling  • •'  143  145  147  L I S T OF FIGURES Figure 1  Page D i s t r i b u t i o n of larch casebearer  i n Canada  ( f r o m Webb a n d Q u e d n a u , 1971) 2  L i f e c y c l e o f Coleophora ( a f t e r Webb 1953)  3  Larch f o l i a g e and  13  larice!la  . . .  showing  20  long shoot, short shoots  f a s c i c l e s o f needles  29  4  The s t u d y a r e a , a s t a n d o f w e s t e r n  5  C a s t l e g a r , B r i t i s h Columbia Map s h o w i n g s t u d y a r e a s ( a f t e r S h e p h e r d a n d Ross,  6abc  32  . 33  L i f e stages o f the larch casebearer fascicles  showing  sampled  a.  Needle  b.  damage t o n e e d l e t i p s , a n d pupa Eggs o n a d v e n t i t i o u s new n e e d l e s .  c.  8  near  1973)  C o u r t e s y o f The P a c i f i c  7  larch  spring feeding  Forest Research  O v e r w i n t e r i n g c a s e s on dormant  Diagram showing a t T h r u m s , B.C a.  37  larch  C e n t r e . . . .38  twig  r e l a t i v e p o s i t i o n s o f sample  39  trees 42  D i v i s i o n o f l a r c h crown v e r t i c a l l y and horizontally  b.  Sample b r a n c h  showing  43  branch s e c t i o n s  (6)  selected 9 10  C o l l e c t i o n a n d R e a r i n g bag w i t h Frequency per  11  12  13  43  distribution  15 cm branch _  Frequency  branch  section.  . . 51  o f i n s e c t s p e r f a s c i c l e and  section:  distribution  15~cm  a) pupa  '7^;  b) pupa  '75  . . . .  67  o f eggs p e r f a s c i c l e and  p e r 15~cm b r a n c h  section  68  The r e l a t i o n s h i p  b e t w e e n mean number o f i n s e c t s  p e r f a s c i c l e a n d v a r i a n c e : a ) L a r v a ^ ; b) Egg  70  Number o f i n s e c t s  82  per f a s c i c l e  - xi-  by c r o w n p o s i t i o n  14  Number of pupae per f a s c i c l e : a) by tree and crown position; b) by exposure, branch position and tree, 197^+ - -83  15  Number of eggs per f a s c i c l e : a) by tree and crown position; b) by exposure, branch position and tree,  16  Number of prewinter larvae per fascicle-: a) by tree and crown position; b) by exposure, branch position and tree, 1974  85  Number of insects per f a s c i c l e by exposure and branch pos i t ion  86  Number of insects per f a s c i c l e by horizontal crown pos i t ion  88  17  18 19  Four l 5 c m branch sections -  2,  20  21  1974.84  showing d e f o l i a t i o n ratings  4 , 6 , 10  97  Number of casebearer per 15~cm branch section by crown levels . Casebearer population per f a s c i c l e from May to June 1975  .105  197** 138  - xii -  Appendix  LIST OF APPENDICES  Page  1  Pupa] data sheet and sampling notes  159  2  Form used for egg counts  161  3  Form used for larval counts  162  4  Tables 1-25  163  Table 1  Observed and expected frequencies for pupae per f a s c i c l e per 15~cm branch section  .163  2  Observed and expected frequencies for pupae per 15 cm branch section  164  3  Observed and expected frequencies for eggs per f a s c i c l e per 15~cm branch section  165  4  Observed and expected frequencies for larvae per f a s c i c l e per 15~cm branch section 1 9 7 4 - 7 5  -  166 . • •  5  Observed and expected frequencies for larvae per 15-cm branch section 1 9 7 4 - 7 5  167  6  Analyses of variance of eggs per f a s c i c l e by tree, crown l e v e l , exposure, branch type and horizontal crown pos i t ion  168  7  Analyses of variance of prewinter and postwinter larvae by tree, crown l e v e l , exposure, branch type and horizontal crown position  169  8  Analyses of variance of pupae by tree, crown l e v e l , 170 exposure, branch type and horizontal crown p o s i t i o n .  9  Average number of insects per f a s c i c l e by tree and position in the stand  171  10  Avg.No.of insects per f a s c i c l e by tree and crown pos i t ion, 1974  172  11  Avg.No.of insects per f a s c i c l e by tree position in stand and crown position, 1975  173  12  Avg.No.of insects per f a s c i c l e by tree position in stand and exposure, 1 9 7 4 . .  174  13  Avg.No.of insects per f a s c i c l e by tree and exposure, 1975  - xiii: -  175  14  branch type, 15  176  Avg.No. of insects per f a s c i c l e by tree and  197** 177  Avg.No. of insects per f a s c i c l e by tree and branch type, 1975  16  Avg.No. of pupae per f a s c i c l e by tree, branch type and horizontal crown position, 197**  178  17  Avg.No. of eggs per f a s c i c l e by tree, branch type and horizontal crown position, 197**  179  18  Avg.No. of prewinter larvae per f a s c i c l e by tree, branch type and horizontal crown position,  180  Avg.No. of postwinter larvae per f a s c i c l e by tree, branch type and horizontal crown position, April 1975* • •  181  197**  19  5  • • •  20  Avg.No. of pupae per f a s c i c l e by tree, branch 182 type and horizontal crown position, June 1975« • • •  21  Avg.No. of eggs per f a s c i c l e by tree, branch type and horizontal crown position, 1975  22  Avg.No.of insects per f a s c i c l e by crown level and exposure •  184  23  Avg.No. of insects per f a s c i c l e by crown level and branch type  184  2k  Avg.No. of insects per f a s c i c l e by branch type and exposure  184  25  Average number of f a s c i c l e s per 15~cm branch section by tree and c o l l e c t i o n period  185  I  Frequency d i s t r i b u t i o n sect ion . . . ,  ||  Relationship between variance (S ) and mean (x) of f a s c i c l e per 15 cm branch section by tree. . . . . 186 -  - xiv -  183  of f a s c i c l e s per 15 cm -  branch 186  ACKNOWLEDGEMENTS  Sincere thanks are due to-Dr. K. Graham, Professor of Forest Entomology, University of B r i t i s h Columbia for guidance and advice; to Dr. A. Kozak for advice on s t a t i s t i c s ; to the other members of my advisory committee, Drs. A.D. Chambers, J.H. Meyers and P.G. Haddock for helpful c r i t i c i s m of the preliminary draft of the thesis; and to Dr. D.A. Ross, Research S c i e n t i s t , and other members of the staff at the P a c i f i c Forest Research Centre, V i c t o r i a , B.C. for their interest and support of the project. I express sincere thanks also to the Faculty of Forestry, University of B r i t i s h Columbia; the National Research Council of Canada; and the Canadian Forestry Service, P a c i f i c Forest Research Centre, for financial assistance and support.  - xv -  INTRODUCTION  It has become v i r t u a l l y axiomatic that the design of population sampling  systems can be prescribed within the framework of certain  general p r i n c i p l e s .  F i r s t , the sampling  Then that universe must be subdivided  universe must be defined.  into component " s t r a t a " having  known, apparent, or presumedly d i s t i n c t features.  Samples must be  taken so as to represent either an average condition or a particular one.  A s u f f i c i e n t number of samples must be taken to express with an  acceptable level of confidence the particular parameters which are being sought. A p r i n c i p l e to be recognized  is that population  systems must be designed d i f f e r e n t l y in detail  sampling  to serve d i f f e r e n t purposes.  The purposermay be to achieve a sensitive means of detecting low population densities, to express  r e l a t i v e levels of populations in time and place or  to detect r e l a t i v e density patterns.  It may  seek to estimate absolute  populations per unit of t e r r a i n , or saturation density of a population r e l a t i v e to the available food supply. Another recognized p r i n c i p l e is to define times  in the  life  cycle when the population is stable numerically or s p a t i a l l y , or presents a particular feature of interest or f e a s i b l e opportunity. hand a complete sequence of insect stages from egg for  l i f e table purposes.  On the other  to adult may  be required  - 2 -  A particular guideline is the d e f i n i t i o n of appropriate sampling  universes where the insect w i l l be found at d i f f e r e n t  during i t s l i f e . of  This necessitates an understanding  times  of the biology  the s p e c i f i c insect, and cannot be derived from general knowledge. Every species of insect presents a rather special problem  which d i f f e r s  in various ways from every other insect.  This follows  from the fact that i t has a d i s t i n c t pattern of l i f e cycle and habits as i t progresses ontogenetically from egg to adult. certain consistent tendencies  Each species reveals  in the general location of i t s various  life  stages as they s h i f t from one microhabitat to another under the dictates of  their genetic code and  internal  influences.  However, the loci of  population concentrations within any given microhabitat vary according to circumstance.  Such s h i f t s of population concentrations within d i f f e r e n t  parts of a microhabitat can reduce the accuracy of a sampling  system which  does not provide for this factor. Sampling design must recognize special features of the on which insects occur.  On a tree, special features of crown form,  branches, twigs and foliage must be taken It was  into account.  in the light of these considerations that i t has been  necessary to devise a sampling  design that meets the s p e c i f i c problems  of measuring populations of the larch casebearer Coleophora (Hbn)  substratum  Coleophoridae:  laricella  Lepidoptera.  In accordance with the foregoing p r i n c i p l e s , the l i f e history and habits of the larch casebearer of  a sampling  of  the biology of £. lar i c e l l a  form an essential basis for the design  system e x p l i c i t l y applicable to this species. is presented  An account  in the f i r s t section following  this INTRODUCTION, being so placed in order that the information is close  - 3 -  at hand, but w i l l not interrupt the continuity of the statements concerning the problems of sampling. The larch casebearer is an important forest defoliator of various species of larch (Larix spp) throughout the world, including western and eastern North America. on western  larch (Larix occidental is Nutt.) in Idaho, U.S.A. in  and in southern B r i t i s h Columbia are of  The casebearer was f i r s t discovered  in 1966-  1957  Suitable sampling techniques  now required to study the population of this insect and the effects native and/or  introduced control factors.  Sampling procedures heretofore available for the larch casebearer l e f t certain matters unresolved for their direct application to western larch: (i)  they were based on r e l a t i v e l y meagre samples,  (ii)  they were not suitably s t r a t i f i e d  into the different segments  of diverse and widely varying sampling universes, (iii)  they related to species of larch other than L_. occ i denta 1 i s growing  (iv)  in other biogeographica1  regions,  they were based on a fixed design of sampling which did not provide for the distortions of the spatial d i s t r i b u t i o n of the insect populations under various influences. It is the purpose of this investigation to test the hypothesis  that s h i f t s in population concentrations of the larch casebearer influence the accuracy of sampling at fixed points in the crown of a tree. As a corollary, the further hypothesis would follow that sampling accuracy would improve by a s h i f t of sampling intensity according to circumstances noted above.  -4 -  The pursuit of these objectives was perceived as requiring procedures to: (1)  ascertain the d i s t r i b u t i o n , s h i f t s in d i s t r i b u t i o n , and v a r i a b i l i t y of insect stages in the tree crown,  (2)  observe the behaviour of a l l insect stages as i t affects population d i s t r i b u t i o n , and  (3)  develop an e f f i c i e n t , s t a t i s t i c a l l y r e l i a b l e sampling for the larch casebearer on western  system  larch in B.C.  The purposes of such a system would be to develop an e f f i c i e n t  sampling  for biological evaluation of infestations at d i f f e r e n t times, places and circumstances.  Such a design would serve the needs of l i f e - t a b l e studies.  The design would also a s s i s t in the formulation of important forest resource management decisions.  As a possible improvement on existing  sampling designs a more accurate yet economical design would a s s i s t in the evaluation of the effectiveness of any control methods. application now  A prospective  in sight would be in the assessment of attempts at biological  control which is expected to follow the proposed  release of parasites.  The experimental sampling for this study was done in immature stands of western larch, infested with the casebearer, near Thrums and Castlegar in the Nelson Forest D i s t r i c t , B.C.  in 1974  and  1975-  E a r l i e r Work  Various methods have been employed to sample larch casebearer population and Eidmann  (1965)  (I965) and  infestation.  (1942), Burst and Ewald ( 1 9 5 5 ) , (1968) in Europe; and Webb (1953), Sloan  Jung  and Schindler  others in North America, are writers who  have related  larval  -5 infestation to the needle f a s c i c l e s of larch which, depending on a tree's intensity of growth, may  (1953)  Webb  contain up to kO needles each. in eastern North America used population i n t e n s i t i e s '  in his study to investigate short-term relationships between the casebearer (insect) and tamarack, J_. l a r i c i n a  (host).  For intra-stand studies counts  were made on the number of casebearers at three crown levels, as found on shoot growth of the previous year bearing 100  lateral spurs.  Usually two  or more shoots were included, these selected in order from the terminal toward the base of the branch, and spurs were counted beginning from the tips of the shoots.  He found a highly s i g n i f i c a n t variation in population  density between crown levels, greater than that between trees, with larvae per spur shoots ratios usually highest at the base of the crown and decreasing toward the tree top. Most of the other workers sampled casebearer populations using the method of Webb  (1953).  For example, Sloan  (1965)  sampled the casebearer  in Wisconsin, using Webb's method and taking 3 branches of each of three crown levels.  The data were used to i l l u s t r a t e the seasonal fluctuations  in populations.  However, unlike Webb  (1953)  who  used the analysis of  variance, Sloan claimed that the data were d i f f i c u l t to analyze with normal parametric s t a t i s t i c s , as the sampling procedures  included several populations  about which very few s t a t i s t i c a l assumptions were made. non-parametric  Friedman test was  used for data analysis.  s t a t i s t i c s are useful when the nature of the theoretical  Therefore, the Non-parametric distributions  was not specified; thus, i t is a comparison of ranking and signs.  1  Population intensities is an expression of insect number in terms of available food, e.g. numbers of insects per needle f a s c i c l e s (Morris  1955).  -6 -  Also according to Sloan branch growth.  (1965)  eggs were not found on the older  Consequently he sampled only the new growth.  He is the  only one to mention this, but did not state how he arrived at such a conclusion. Ciesla and Bousfield  (197*0  developed a means of predicting  potential d e f o l i a t i o n by larch casebearer, by using counts of overwintering larvae to forecast regional or forestwide population and damage trends. For  the expression of population densities of overwintering larvae they  adopted Webb's  (1957)  index (number of larvae per  100 spur  unit of measure in their study in northeastern Washington, and western Montana.  shoots) as the  northern Idaho  The system consisted of k branch samples of 100  shoots each collected from mid crown of 10 dominant or codominant larch ,  30 to 50 f t . (10  branches/plot (63  to 16 meters)  spur  western  in height, for a total of 40  plots) during November and December.  They assumed that the relationship with respect to population densities in the crown (upper, mid and lower) of eastern larch held true for  larch casebearer in western larch.  Because accurate counts of the  small overwintering larvae require laboratory examination rather than f i e l d counts, a plan with a fixed rather than a variable number of samples (sequential sampling) was developed by Ciesla and Bousfield Andrews, et_ a_L  (1967)  stated that no standard method of  sampling larch casebearer has been developed. larvae were used i n i t i a l l y  (1974).  Three methods for sampling  in B r i t i s h Columbia by the Forest Insect and  Disease Survey Team to compare results and establish a sampling pattern, they are:  -7 -  (1)  A sample of 5 randomly chosen 12-inch (30 cm) branches from the lower crown from each of 5 trees (in early June for f i n a l  instar  1arvae). (2)  The sequential sampling method used in New Brunswick was  tried at 5 l o c a l i t i e s .  (Webb, 1957)  In this method 100 f a s c i c l e s on a  shoot constitute one sample unit. (3)  A sample unit of ten 16-inch (40 cm) branches taken from the lower crown from each of 5 trees at 5 l o c a l i t i e s was taken in October (for prewinter larvae) to estimate the population density of the succeeding generation.  No conclusive results were obtained  as to the s u i t a b i l i t y of these methods for sampling the casebearer. Ultimately, the 18-inch (45 cm) branch sample normally used in insect surveys was adopted for use in the year Eidmann  (1965)  1968.  in an ecological study on the larch casebearer  in south Sweden, found most eggs and prewinter larvae on shots of the preceding year. youngest  In spring, larval  infestation was heaviest on the  growth. Jagsch  (1973)  constructed l i f e - t a b l e s for the larch casebearer  in the natural areas of d i s t r i b u t i o n of Lar ix dec idua in the Alpine area of S t y r i a , Austria.  His sample unit consisted of about  150-200  terminal  shoots, each about 30 cm long and taken from d i f f e r e n t parts of the tree, from d i f f e r e n t trees and from d i f f e r e n t parts of a stand.  Deficiencies of Former Methods  These methods do not c l e a r l y account for the highly s i g n i f i c a n t variation in population between crown levels and the non-uniform d i s tribution within branches.  -8 New shoots offer f l e x i b l e sample size and ease of c o l l e c t i o n , but shoot numbers lack s t a b i l i t y .  That i s , the number of shoots can vary  considerably with i n t r i n s i c factors such as flower production and effects of repeated d e f o l i a t i o n . jected  This unit of population intensity must be re-  in absolute population work. A r e s t r i c t e d part of the branch, such as the apical 18 inches  {kS  cm) of the branch in Canadian Forest Insect Survey work, 15 inches  (38  cm)  in the U.S.A. and the apical second year's growth by Webb and  others for the larch casebearer provide f l e x i b i l i t y of sampling design and are e a s i l y c o l l e c t e d .  However, the proportion of the insect population  using the sampling unit as a habitat is not constant.  It is affected by  b i o t i c and a b i o t i c factors, such as temperature differences and feeding preferences, resulting in a s h i f t  in center of a c t i v i t y of the population.  Depending on time of c o l l e c t i o n , therefore, the apical portion of the branch may  support d i f f e r e n t proportions of the total population (eggs,  larvae or pupae).  Therefore the use of partial branches may introduce  a bias because of non-uniform d i s t r i b u t i o n of casebearer on the twig. A restricted part of a branch does not lend i t s e l f to quantitative assessments of the total number of units per tree and per acre. it may  Although  be calculated, i t would be very d i f f i c u l t to account for the basal  components of the branches and for their insect population relevant to the t i p s .  Also, 2nd year twigs lack s t a b i l i t y  quantity and quality of new shoots produced.  i.e. they vary with the These weaknesses point to  the need for sampling involving the whole length of the branch. While several population sampling procedures have been described above for estimating populations of the larch casebearer, the possible needs to s h i f t the aim at d i f f e r e n t sampling targets at d i f f e r e n t times of the season and different stages of an infestation have not been e x p l i c i t .  -9 It might be expected that with an i n f l e x i b l y prescribed design of sampling, the accuracy of sample estimates may change as the population s h i f t s within the crown of a tree throughout a season. Inasmuch as one of the major requirements in sampling is to achieve the best gain in accuracy or s e n s i t i v i t y within the shortest time and least cost of labour, an understanding of the conditions affecting the results is desirable. Shifting of the d i s t r i b u t i o n s might be expected to result from mass movements of larvae  upward, downward, inward, or outward on  the crown, according to the particular larval  instar, the state of  hunger, diet, and day-by-day responses to l i g h t , temperature, humidity, wind, atmospheric pressure, gravity, residual amount of foliage, and differences in mortality. The r e l a t i v e s h i f t s of population concentrations might be expected to d i f f e r between trees in d i f f e r e n t positions r e l a t i v e to the stand margins or center.  If such s h i f t s occur in population con-  centrations, they should be recognizable in successive sample estimates of the population. Also, i f s h i f t s of concentration are measurable, they may be correlatable with observable factors, which in turn may provide some guidelines for sampling.  - 10 -  THE  INSECT  Taxonomy  The larch casebearer, Coleophora  laricella  (Hbn) belongs  to the family Coleophoridae in the large group of microlepidoptera of the superfamily Tineoidea. and the f i n a l  Since this species of insect infests larch  larval stages l i v e in a case, i t was given the name  "larch casebearer".  Also the word Coleophora means "bearing a sheath"  and the word l a r i c e l l a refers to " l a r c h " , the ending -el la meaning "small". Common names:  In the l i t e r a t u r e of other languages, the larch casebearer  is found under such common names as:  Larchenminiermotte  (German),  larktradsmalen (Swedish), lariksmot (Dutch), porte-case du meleze (French), la coleofora del l a r i c e ( I t a l i a n ) , la minador del alerce (Spanish). Synonymy:  As an aid in the search of the l i t e r a t u r e the synonymy for  £. l a r i c e l l a is l i s t e d Tinea l a r i c e l l a Hbn.  in chronological order (after Sloan  (1914); T.  l a r i c i n e l l a Bechst., Blum.  Eupista l a r i c e l l a Hubner, Haploptilia l a r i c e l l a , Hubner  J_.  1965): (1816);  (1825);  (1827); Ornix argyropennel 1 a T r e i t (1834); Graci1laria l a r c e l l a Zel1. (1838) ; Colephora l a r i c e l l a Zell (1839); T. larcel la Ratz (1840); H_. l a r i c e l la (Hbn.) Banks (1925) Eupista l a r i c e l l a (Hbn.) Pierce, Metcalf (1935); £• nigricornis Hein. and Wck., Tol1 (1944). l a r i c e l la Hbn. Samm. Europ. Schmett  -11Related species (evidence and significance i f any):  The taxonomy of the larch casebearer appears to be in doubt. In the Soviet Union, Fal'kovich  (196*0  has reported three species of  Coleophora on larch; C_. 1 arieel 1 a (Hbn) , which infests Larix decidua in western and eastern Europe (including the Carpathian region), and two new species described from adults of both sexes as £. s i b i r ica and  datu r i ca spp. n. both previously identified as C_. 1 a r i eel l a .  £. s i b i r i c a mostly infests j^. s i bi rica and occurs in European Russia and in Siberia (as far as the Baikal area), and £. dahurica feeds on L^. dahur ica in eastern Siberia and the Soviet Far East.  Divergence from  an original casebearer species appears to have resulted from the isolation of areas of d i f f e r e n t larch species in the Tertiary period. In Japan, Moriuti  (1972)  stated that for many years the larch  casebearer has been misidentif ied as the European C_. l a r i c e l l a .  The  Japanese species was described from the adults of both sexes as C_. long i s ignel1 a sp.n. H. Pschorn - Walcher 1974)  (personal l e t t e r to Dr. R.F. Shepherd,  speculated as to whether C_. l a r i c e l la is really a truly European  species.  He noted that "taxonomically" i t is quite isolated among the  European Coleophoridae and has only 2 synchronized parasites as compared to 7 f o r the birch casebearer C_. fuscedinel la. The source of western U.S. and western Canadian population is unknown and may have been the U.S.S.R. by way of Japan (Shepherd and Ross,  1973).  This taxonomic problem should be investigated by comparing the  casebearers from Europe, Siberia, Japan and eastern and western North America f o r s p e c i f i c difference.  However, in spite of these taxonomic  -  12 -  differences, there is no apparent difference in the l i f e histories and behaviour except those due to climatic differences.  World Distribution  The larch casebearer occurs in Europe from the French Alps and Italy northward through Austria, Germany and Holland, southern and central Russia to Finland and the Carpathians.  According to the l i t e r a t u r e ,  l i t t l e is known about the casebearer in eastern Europe (e.g. Poland). The casebearer is present in Siberia, in northern China and Japan and probably wherever larches occur.  It followed introduction of larch into  Sweden and Great B r i t a i n . According to Jagsch ( 1 9 7 3 ) ,  in the Alps i t occurs up to tree line,  but mass infestations are rare above 1,600 m ( 6 , 3 0 0 feet) (Eidmann, 1 9 6 5 ) . The f i r s t North American report was by Hagen (1886) Massachusetts  on introduced European larch.  from Northampton,  The larch casebearer  occurs throughout  the range of tamarack (Larix l a r i c i n a  from eastern U.S.  to central Minnesota; and  now  (Du Roi) K. Koch)  in Canada (Fig. 1) from the  A t l a n t i c Provinces and as far north as 4 9 ° - 5 0 ° N. latitude in Quebec and Ontario.  Recently i t has been discovered progressively westward from Lake  Superior to the Manitoba border in western Ontario and covered 1971).  in 1965 was  dis-  in the extreme southeastern corner of Manitoba (Webb and Quednau,  Figure 1.  Distribution  of  larch casebearer  fn  Canada ( f r o m Webb a n d Q u e d n a u ,  1971).  - ]h -  In 1957 the casebearer was discovered on western larch (_L. occ idental is Nu tt.)  in north-central  States, approximately 1,700 miles infestation in Minnesota Columbia  in 1966.  (2,735  km) from the last reported  (Denton and Tunnock, 1972) and in B r i t i s h  Its current d i s t r i b u t i o n encompasses most of the  range of western larch in Washington, approximately 200 miles (322 B r i t i s h Columbia  Idaho in northwestern United  Idaho and Montana and a s t r i p of  km) along the international boundary in  (Webb and Quednau, 1 9 7 1 ) .  The northern limit and a l t i t u d i n a l  limit of the larch casebearer  does not extend as f a r northward or upwards as the host range. (1963) explains the northern limit of Z. l a r i c e l l a factor of the vegetative period of the host.  Eidmann  in Europe as being a  The casebearer is k i l l e d  when cool summers are followed by early winters.  Cool temperatures  appear to be the indirect cause of the insects death as such low temperatures reduce the vegetative period to the extent that there is i n s u f f i c i e n t time for the insect to prepare for dispause.  A normal  dispausing larva is able to survive temperatures approaching -30C (-22F).  Significance as a Defoliator  The larch casebearer has been a perennial d e f o l i a t o r of larch in Europe for centuries and has always been considered a serious pest. Currently i t is the most serious pest of western  larch.  Severe d e f o l i a t i o n or rather needle-mining of a healthy tree is i n i t i a l l y followed by r e f o l i a t i o n later in the same spring.  Defolia-  tion in successive years causes reduced production of foliage and shoots, reduction of terminal and radial growth, death of scattered twigs and branches, to death of the tree.  - 15 Diameter growth can be d r a s t i c a l l y reduced by repeated casebearer d e f o l i a t i o n . increment  Schwerdtfeger  and Schneider  (1957)  calculated  losses of 35 to 45 percent a f t e r several years of continuous  severe feeding.  Denton  f o l i a t i o n on radial  (1964)  showed i n i t i a l  increment on western  casebearer damage in 1956,  results of repeated de-  larch in Idaho.  Prior to  the larch trees added 4.0 mm radial  increment.  After f i v e years of severe d e f o l i a t i o n increment had decreased to 1.0 representing a 75 percent reduction in growth.  During the same period  annual growth of non-defoliated larch trees decrease from 4.4 or a reduction of  23 percent.  mm,  According to Tunnock, et a l .  to 3-** mm  (1969)  there  is evidence of radial growth loss of up to Sk percent in areas of Idaho where severe d e f o l i a t i o n has occurred for four or more consecutive years. Effect of d e f o l i a t i o n on height growth can be severe. Burst  (1959)  found that height increment was retarded  years of larch casebearer feeding.  Ewald and  17 percent  in four  Larch, being a serai species exhibits  a high degree of shade intolerance and i t can survive only i f i t maintains a dominant position in the canopy (Roe, et a l .  1971).  Repeated d e f o l i a t i o n  reduces the growth of larch and places i t at a competitive disadvantage with i t s associated species.  Accordingly, larch can lose i t s dominance  in mixed stands and eventually i t s potential to recover even though the casebearers population may decline.  Growth reduction and loss of tree  vigor can have serious long-term forest resource management implications with or without mortality of larch. In eastern North America, Herrick  (1912), Craighead (1950)  among the t r e e - k i l l i n g insects.  several entomologists and Dowden  (1957)  list  including larch casebearer  In Europe there are r e l i a b l e reports  of trees dying after casebearer d e f o l i a t i o n , Jung  (19^+2)  and others c i t e  - 16 instances of larch mortality following outbreaks. Webb  (1953)  Others, such as  suggest that i t is unlikely that the casebearer alone can  cause tree mortality of tamarack in the east, but concluded that i t might be a contributing factor.  In Europe, casebearer feeding  reduces  the vigor of the trees and allows the larch canker fungus (Dasyscypha willkommi i (Hart.) Rehm.) In 1967,  to enter and eventually k i l l  ten years after the casebearer was discovered on  western larch, mortality was reported Idaho.  In 1968  the tree.  in the St. Joe National  Forest,  aerial surveys confirmed that serious deterioration and  tree mortality were prevalent within thousands of acres of larch forests in Idaho.  However, a study to determine the cause did not confirm  that  larch casebearer was the sole cause of tree mortality but that i t was d e f i n i t e l y responsible for weakening and predisposing to mortality (Tunnock, et a l .  western larch stands  1969)-  Biological Characteristics of the Insect  The significance of the b i o l o g i c a l c h a r a c t e r i s t i c s of the insect as a background to sampling is summarized below: It is necessary to know what s p e c i f i c object  is to be sought  i.e., the insect during any or a l l of i t s morphological forms as they metamorphose throughout l i f e from egg to adult. It is necessary to define the l i f e cycle because this provides the guidelines for knowing when any p a r t i c u l a r stage w i l l what stage w i l l be found at any prescribed  time during  be found or  the l i f e cycle.  - 17 -  It is necessary  to have a knowledge of the behaviour and habits  in order to know where to sample; so that the sampling e f f o r t s can be directed to s p e c i f i c points in the nabitat any time of the season, time .' of day or under various circumstances  which might affect the d i s t r i b u t i o n  patterns.  Morphological  Forms and Stages  Descriptions of adults, eggs, larvae, and pupae serve as a basis for s p e c i f i c search and i d e n t i f i c a t i o n of the pest. of the larch casebearer were described by Webb Adu11:  stages  (1953) •  This is a small s i l v e r y to greyish brown moth, with no conspicuous  markings; wing expanse 9 mm (3/8 h a i r l i k e scales. appearing  inch), narrow, fringed with long slender  Maie - dull slate-gray, the sides of the abdomen  almost straight and p a r a l l e l , and the claspers give the anal  extremity a bifurcated appearance.  Fema1e - Lighter gray than the male  also s i l v e r y on the vental part of the abdomen. giving a more robust appearance. Egg:  The l i f e  Sides of the abdomen  Tip of abdomen abruptly truncated.  The eggs are hemispherical with 12 to 14 lateral  ridges radiating  from apex to base and under magnification resemble inverted j e l l y molds-. They are orange-yellow to clear gray just before hatching, however, reference to their color varies from cinnamon-rufous to reddish brown. Average diameter is 0.29  mm and average height 0.17  mm.  The f l a t lower  side is cemented to the needles by a transparent substance.  - 18 -  Larva: 1.0 mm  The  larvae develop through four instars.  in length; mean head width of 0.11  f i n e ferruginous markings.  mm;  F i r s t instar averaging  color honey-yellow, with  Head pale brown, darkening  along the epicra-  nial suture, thorax s l i g h t l y wider than abdomen; thoracic legs and  small  prolegs well developed; abdominal proleg not d i s t i n c t . Second instar larvae averaging width 0.15  mm,  1.4 mm  abdomen with brown pigmentation,  in length, mean head thorax darking dull brown,  head dark brown. Third instar larvae, average 1.8 mm 0.24  mm,  in length; mean head width  abdomen darker brown, head capsule black, inside a tubular case  made from a hollowed-out needle which is yellowish in color and  rectangular  in shape. Fourth head width 0.33  instar or mature larvae average 4.3 mm mm.  in length; mean  abdomen liini'fiorm dull brown in color, head and thoracic  shield black, divided along the mid-dorsal  l i n e , the larva is inside an  enlarged tubular case. Pupa:  The pupae are obtect, dark brown without  features; size varies from 2 to 4 mm  (av. 3 mm)  d i s t i n c t i v e markings or  in length and  slightly  less than 1 mm wide; i t is inside a greyish cigar shaped case about 4 mm long.  - 19 L i f e History  The l i f e history of the larch casebearer has been studied in other regions of the world by many investigators, including: Reissig and Ratzeburg Eidmann  (1869) ,  (1965)  Escherich  (1931)  and Jung  in southern Sweden, Herrick  (19^+2)  in West Germany,  (1912, 1929, 1935) and  Webb  (1953)  in eastern U.S.A. The larch casebearer has one generation each year. emergence occur from mid-June to early July.  The eggs are laid singly  and scattered over the f o l i a g e in late June to July. larvae bore d i r e c t l y to second  Adult  The newly hatched  into the needles and start mining.  Larval development  instar larvae range from late July to late August.  Third  instar  larvae, the casebearing and overwintering stage, occur from late August to early May.  The fourth and f i n a l  instar larvae feed throughout  pupation begin in late May and extends  May,  into the middle of June (Fig. 2).  Reproduction, Growth S Morphogenesis  Reproduction:  1953)-  The adults emerge in June; normal sex ratio is 5 0 : 5 0 (Webb,  This bisexual ism requires mating and renders their  vulnerable to meteorological influences.  fertility  The moths-are crepuscular,  mating takes place 1 or 2 days after emergence and is stimulated by decreasing l i g h t .  The female is pro-ovigenic having i t s f u l l complement  of eggs at time of emergency. According to Quednau  (1967)  egg laying was 70 to 80 F females was  66.6+ 3.1,  Peak oviposition occurs during the f i r s t week. in Quebec, Canada, the optimum temperature for  (21 - 26.7C)  range  48-111,  average of 50 eggs (maximum 133)  and oviposition by average-sized eggs (compared to Webb's ( 1 9 5 3 )  deposited by f i e l d mated females in  I nsect Stage  Winter  Apr i 1  May  June  July  Aug.  Sept.  Oct.  Larva^ f o l i a t i o n of larch, Pupa  resumption of feeding  Adult  Egg O  Larva  1-2  Larva.  Fig.  2.  Life-cycle of Coleophora l a r i c e l l a  (after Webb  1953)-  - 21 -  laboratory cages at room temperature). females  is  15 days  (Quednau  The average  1967).  The embryonic development lasts 10-20 temperature, Larvae:  12 days  80-85°F (26-29C)  at  After hatching the f i r s t  side of the egg d i r e c t l y the empty egg cases.  l i f e span of the  days, depending on the  according to Quednau  (I967).  instar larvae bore through the under-  into the needles, the i n i t i a l  During the f i r s t  two larval  faeces f i l l i n g  instars, the cater-  p i l l a r s mine the needles for about 6 weeks after which they moult to the third  instar.  The larva now makes a. case from the hollowed-out  needle and continues to feed on the f o l i a g e in the late summer until the needle moisture'content f a l l s and nourishment decreases while the photoperiod shortens.  Just before needle-fall the larva firmly attaches  its case with s i l k threads to various parts of the branch. The winter dormancy lasts until appearance of new  bud-burst or until  the  larch needles, i.e. u n t i l mid or late April  areas or u n t i l mid-May at higher elevations.  in low-lying  The larva molts to the f i n a l  instar, resumes feeding as a casebearer and enlarges i t s case.  Before  feeding, the casebearer fastens i t s case firmly to a needle with a pad of  s i l k threads and mines the interior as far as the larva can reach  without leaving i t s case.  After a feeding period of 3 to k weeks, the  larva attaches i t s case to a needle or center of a needle f a s c i c l e and pupates. The pupal resting stage last about 2 to 3 weeks, after which the moths emerge and the l i f e cycle is i n i t i a t e d again.  - 22 THE HOST TREE  The variations in the d i s t r i b u t i o n of the insect and i t s damage may be linked with some character of the environment including i t s host species.  The larch casebearer occurs within certain approximately  definable t e r r i t o r i a l and climate.  limits with boundaries affected by host a v a i l a b i l i t y  Therefore, i t is necessary to know the d i s t r i b u t i o n of the  preferred host and of insect damage, as well as the d i s t r i b u t i o n of certain other environmental  factors such as, habitat type, stand age and density for  the development of sampling designs to serve the various needs of resource management.  Host species and S u s c e p t i b i l i t y  Tree species of the genus Larix are the preferred hosts of the larch casebearer.  A l l ages and vigor of larches are attacked.  and old trees are attacked mainly at the intermediate altitudes  (2460-4265 feet) Columbia.  (Eidmann  I965)  and below  3000  Young  750~1300m  (1000 m.)  feet  in B r i t i s h  Greatest effects are probably on the younger trees which are  in competition with associated species. Attacks on conifers other than species of Larix are rare, and then probably represent biological accidents or circumstance, such as attacks on understory trees during severe infestations.  Peirson  (1927)  reported larvae feeding on white pine, Pinus strobus L. and f i r , Abies sp. where opening buds were preferred. Schwarz  (1933)  In Europe, Van Poeteran  (1933)  found the larvae feeding in needles of Douglas-fir,  Pseudotsuga menziesii (Mirb.) Franco, (Webb,  1953);  Eidmann  (1965)  and  - 23 reported  that i t also infests to some extent Douglas-fir  neighbourhood of larch in south Sweden.  Luitjes  (1971)  in the investigated  the development of the larch casebearer on young Douglas-fir  planted  in 1965  (1eptolep i s)  under a thinned  in Holland. October,  stand of 35 year old Larix kaempferi -  Despite a reported  19% of  larval mortality of over 30% in July-  the needles were damaged in  1966  and 26% in  To date the larch casebearer has not attacked  1967•  sub-alpine  larch L_. lyal 1 i P a r i , in B r i t i s h Columbia or western U.S.A., but this is possibly due feet  to the extreme climate in i t s range at altitudes 7,000-10,000  (2133~30^+8  larch.  m)  in the environment at timberline isolated from western  Early reports l i s t Japanese and  to the casebearer, but  Russian larches as resistant  infestations have been reported on both.  studies on s i t e differences have been carried out reported without explaining why attacked  in Europe; Jung  that in a certain area one tree  heavily while neighbouring trees were not  This is probably due  Limited  (from Sloan,  to the fact that the casebearer w i l l  (19^*2)  was  1965)-  concentrate  on one tree until forced to disperse. Jung f e l t that s i c k l y trees would be subjected  to heavier  Schimitschek  attacks.  (1963) indicated  that the following stand  conditions  were suggestive of larch casebearer outbreak conditions: (a)  in natural alpine areas, warm slopes;  (b)  effects on the physiological state of the tree (e.g. disturbance  (c)  of water balance by grazing); and  forest history of the area  (e.g. changes in environmental factors  which a f f e c t s the quality and quantity of foliage produced). These conditions are applicable also to outbreaks of other d e f o l i a t o r s .  - 2k -  Schindler  (1965)  in Germany stated that damage by the larch  casebearer is p a r t i c u l a r l y severe in poor quality stands.  The Host Tree in B r i t i s h Columbia  The host tree in B r i t i s h Columbia is western larch occidentalis).  (30-55 m)  The mature western larch is a large tree  in height and 3~k feet  (1m) in diameter.  (Larix  100-180  feet  In B r i t i s h Columbia  its range is (restricted to the southeastern portion of the province: eastward from Okanagan Lake to the flank of the Rocky Mountains northward to Shuswap Lake and Columbia Lake.  1,800-4,000  feet  Altitudinal  range is approximately  (549-1219m).  Western larch occurs in B r i t i s h Columbia in the following biogeoclimatic zones of Krajina 1.  (1965):  the interior western hemlock zone only on the drier subzone (IWH ); a  2.  the interior Douglas-fir zone (IDF);  3.  the ponderosa pine-bunchgrass zone, in the moister pockets.  Such phytosociological delineations are potentially important for purposes of population sampling designs which recognize the need to s t r a t i f y sampling universes according to d i f f e r e n t expectations of insect d i s t r i b u t i o n . The study area and most of the western larch occurs in the drier subzone of the Interior Western Hemlock zone which is characterized as follows (after B e l l ,  1965; Krajina, 1965):  - 25 -  CIimate Regimen:  microthermal continental  humid with no d i s t i n c t l y  dry season Accumulated day degrees over 43F(6C): 1,500-3,000 per year Mean annual temperature: 42-46F (6~8C) Mean monthly temperature January 20-29F (-7 to -12C) July  65-68F (18-20C)  Number of months above 50F (10C) 5 below 32F (0C) 3-4 "  " f r o s t - f r e e days:  Mean annual p r e c i p i t a t i o n : "  "  snowfall:  100-150 20~38 inches (51~96cm) 57~l60 inches (145-^06^)  Seasonal occurrence of p r e c i p i t a t i o n : Wettest season - winter (40% of total  precipitation)  Wettest month usually Dec. or Jan. 2.2-5.1 in. (56-129mm) Driest season - summer (20% ppt) Driest month usually July 0.9-2.4 in. (23"6lmm) Clouds:  very common  Prevailing winds are from the northwest and precipitation is c h a r a c t e r i s t i c a l l y orographic. Soils:  zonal group - Minimal and orthic podzol humus - Ligno-mycelial mor  This subzone is found between longitude 117°5  1  and 119° and  latitude 49°10' and 5 1 ° , and a l t i t u d e 1,400-4,400 feet (427-13^1 m) in the Selkirk and Monashee mountains of southeastern B.C. and to a lesser extent in the Rockies.  -  26  -  General c l i m a t i c requirements of western according to Krajina (a)  (1965) and may  Western larch is adapted  a f f e c t the insect population: to the microthermal  humid climate with a moderately (b)  larch are l i s t e d  continental montane  long vegetative season.  It does not tolerate very humid climate even i f i t s transpiration rate during the vegetative season the spring or during r e f o l i a t i o n  is very high, especially in in late spring after  insect  damage. (c)  It tolerates an average annual p r e c i p i t a t i o n of 28 inches (71cm) up to 35 inches (89cm)  in a few larch stands, and a minimum of  18 inches ( 4 6 c m ) . (d)  Shade tolerance of larch is almost n i l and stands have been maintained over the years by w i l d f i r e or by the clearcut systems of today.  According to Krajina (1965) western  the nutritional  requirements of  larch are moderate, comparable with those of Douglas-fir.  It  grows better in a rich supply of calcium and magnesium, i t s relation to nitrogen has not been studied (Krajina, This subzone (IWH  a  1965).  ) is one of the richest areas of various coni-  ferous tree species in B r i t i s h Columbia.  Western larch is a dominant  species of wide ecological amplitude and grows in mixture with other subclimax and climax species, such as, the climatic climax western hemlock (Tsuga heterophy11 a (Raf.) Sarg) , the edaphic climax western (Thuja p l i c a t a Donn) on wet s i t e s , Douglas-fir  redcedar  (Pseudotsuga menziesii  var. glauca (Mirb) Franco), grand f i r (Abies grandis (Dougl.)  Lindl)  - 27 western white pine (Pinus monticola Dougl.), lodgepole pine (P_. contorta Dougl.).  Associated hardwoods are; black cottonwood  ssp. tr ichocarpa) , trembling aspen  (Populus balsamifera L.  (P_. tremuloides Michx) and birch  (Betula  papyrifera March). The i n i t i a l spread of the larch casebearer was most rapid along the valley bottoms.  (762m)  The insect population decreases at about  2,500  feet  in elevation with few casebearers above this a l t i t u d e in B.C.  (Shepherd and Ross,  1973).  The Host Tree as a Sampling Unit  As an insect sampling problem larch has certain  noteworthy  p e c u l i a r i t i e s in the physical form of the tree, i t s deciduous c h a r a c t e r i s t i c s , and i t s effects on insect behaviour.  These are such that recognition must  be given to unequal and changing d i s t r i b u t i o n s of the insects to the extent that s t r a t i f i c a t i o n of sampling design is required to meet the expecta t i ons. Expectations are that the insect population at any s p e c i f i c period of the season, or time of day, or state of d e f o l i a t i o n w i l l  differ  between base and apex of the crown and between tips and bases of branches within a crown.  Also, the ultimate sampling unit must be the f a s c i c l e  of needles during the growing season.  However, as part of the population  occurs also on the branches, sampling data must relate to s p e c i f i c a l l y prescribed portions of branches and the short shoots associated therewith.  - 28 -  Morphological Characteristics of Larch  Need 1es:  The needles are light green and soft becoming  harder later in the season, and yellow before shedding in the autumn. The needles are 2.5 to 50 mm and with sharp-pointed t i p s .  in length, triangular in transverse section The needles of larch are either in f a s c i c l e s  of 16-40 needles clustered on short spurs, or as single needles arranged s p i r a l l y along the growth of the current year only. Branches:  The branches contain both long shoots or the current  years shoot bearing single needles; and on the older shoots, short shoots bearing terminal clusters of needles: 1.  The shorts shoots are referred to in the l i t e r a t u r e as  "spur shoots", "spurs", "short spurs", " f a s c i c l e s of needles" or "needle fascicles".  In this study the short shoots w? thout i t s complement of  needles are designated as spur shoots, and with needles as f a s c i c l e s . The short spur shoots increase very slowly in length but have each year's growth marked externally by a d i s t i n c t ring of leaf-scars. 2.  The long shoots sometimes called terminal shoots or twigs  have the needles scattered singly and s p i r a l l y along i t s length.  The base  of each elongating shoot is surrounded by peripheral needles of the top of the previous year's growth (Fig. 3 ) .  - 29 -  F i g u r e 3«  L a r c h f o l i a g e showing l o n g s h o o t , s h o r t and Buds: 1.  shcots  f a s c i c l e s of needles. Buds a r e o f t h r e e k i n d s :  Terminal  on t h e l o n g s h o o t s  producing  long o r short  A x i l l a r y on t h e long s h o o t s , s o l i t a r y  i n the needle  shoots. 2.  a x i l s producing  long o r s h o r t s h o o t s  but u s u a l l y the  latter. 3«  From t h e p o i n t s o f s h o r t s h o o t s needles, or flowers  producing  fascicles of  I.e. m e g a s p o r a n g i a t e and m i c r o -  s p o r a n g i a t e s t r o b i l i accompanied by s l i g h t  elongation  o f the shoot, o r l e s s f r e q u e n t l y a long shoot w i t h s p i r a l l y arranged  l e a v e s e s p e c i a l l y under abnormal  g r o w t h c o n d i t i o n s such as d e f o l i a t i o n .  - 30 Deciduous Characteristic of Larch  Significance:  Larches are the only conifers in the stands that are  deciduous, and consequently there are no differences, other than seasonal ones,  in the age of needles upon which the larvae can feed.  Both of these factors simplify the situation with respect to possible q u a l i t a t i v e nutritional differences in larval food (Heron,  1966).  Also being naturally deciduous, larch is much more resistant to d e f o l i a t i o n than other coniferous trees.  Other conifers cannot replace  foliage once i t is lost except by new shoot growth, whereas larch is capable of producing two crops of needles on the same spur during a single growing  season.  Vegetative Cycle  Larch foliage turns yellow in the f a l l , death and shedding of the needles soon follows, and the tree is bare throughout winter. Needles start changing color early in October and by mid-November most have been shed. New needles are produced between mid-April and mid-May.  the following spring, usually  The period between shedding of the  old needles and production of the new f o l i a g e varies somewhat from year to year and with a l t i t u d e or latitude.  - 31 -  THE STUDY AREA,. MATERIAL AND METHOD  Need for Choosing  Sampling Area  The requirements  for selection of stands for studying the  factors which affect population sampling and a c c e s s i b i l i t y .  included homogeneous conditions  The study area was an immature western larch stand  which has been infested by larch casebearer since 1966. typical of the areas infested by the casebearer  The s i t e  was  in B r i t i s h Columbia as  reported by the Canadian Forest Insect and Disease Survey. Local? ty:  The main study area was a larch casebearer  infested stand at  Thrums near Castlegar in the Nelson Forest D i s t r i c t , B r i t i s h Columbia. The stand was  located on private property 1.1 miles (1.8 km) east of the  Thrums elementary  school o f f Highway No. 3-  bottom at an elevation of 1,700 gravelly loam.  The s i t e was  a f l a t valley  f t . (5l8m) with well drained sandy to  The larch stand was dense and the vegetation consisted  of 80 percent western larch, 15 percent understory of redcedar piicata) and 5 percent Douglas-fir (Pseudotsuga  (Thuja  menziesii), western hemlock  (Tsuga heterophy11 a), grand f i r (Abies grandis) and aspen (Populus tremuloides). Shrubs included species common to most areas: Saskatoon berry  (Amelanchier  a 1n i f o l i a Nutt), mock orange, (Philadelphus 1ew i s i i Pursh), snowberry (Symphoricarpus albus (L.) Blake), f a l s e box  (Pachistima myrsinites (Pursh) Raf),  Oregon grape (Mahonia nervosa Pursh), tufted phlox (Phlox caespitosa Nutt). Ground vegetation included:  Mountain l i l y  (Li 1ium montanum A. Nela.),  bearberry or kinnikinnick (Arctostaphylos uva-urs? (L.) Spreng), (Pteridium aquilinum pubescens Underv.), mosses such as, shreber? Mitt and grasses.  bracken  Pleurozium  - 32 -  The study area, a stand of western larch near Castlegar, B r i t i s h Columbia.  - 33 -  S c a l e miles 1  0  10  20  30  Range of Larix occidentalis Distribution of Coleophora laricella 1966-1968  Ww+i  1969-1970  Col lection Sites m 1. 2.  Thrums Sheep Creek  197! - 1972  Map showing study areas (after Shepherd and Ross,  1973).  -  The larch trees ranged 4-8  inches ( 1 0 - 2 0 cm)  34  -  in height from 3 0 - 6 0 feet ( 8 - 1 5  m),  in diameter at breast height (d.b.h.) with green  crown length of over 80 percent of total tree length.  The stand  was  about 30 years o l d . The other study area was  located at Sheep Creek, 5 miles south  of Salmo, B r i t i s h Columbia, just o f f Highway No. 6 and 2 1 . 5 miles (3-**5 in a straight line southeast of the s i t e at Thrums.  km)  The s i t e was at an  a l t i t u d e of 2 , 0 0 0 feet A.S.C. (670m) on a level or gently sloping f l u v i a l plain with s o i l s predominantly a well drained Orthic Regosols.  This stand  consisted of clusters of larch trees mainly, typical of most larch stands in the region.  The larch trees were immature with an average height of  45 feet (14m) and an average diameter at breast height of 6 inches (15  Sampling  cm).  Procedures  The Need for Sampling.  Sampling  is necessary for the following  reasons: (1)  to establish species d i s t r i b u t i o n ;  (2)  to measure population densities and change;  (3)  to construct l i f e tables;  (4)  to make a biological evaluation of natural and  artificial  (introduced parasites, pesticides, etc.) impacts on populat ions.  insect  -  35  -  The Sampling Universe  The  'universe'  represents  the habitat in which the insect  population occurs and must be defined forest f l o o r .  The species range may  in terms of trees, f o l i a g e or be the sampling universe but  i t is  common to refer to stands or habitat within the insect's d i s t r i b u t i o n a l range as the universe. be considered  Any  homogeneous stand of forest may  therefore  a universe, so as to avoid s t r a t i f i e d random sampling from  a heterogeneous universe.  However, in devising sampling methods i t is  necessary to describe the universe more exactly, such as, trees -- considering position of trees in the stand  (edge, i n t e r i o r , open grown),  c h a r a c t e r i s t i c s of trees as units (height, crown, age, etc.) and position in the crown (lower, middle, upper).  Selection of the Sampling Unit  It is assumed that the f a s c i c l e s of needles provide the most appropriate unit.  It is advantageous to base examination of foliage d i s -  t r i b i t i o n on the number of f a s c i c l e s , and  the d i s t r i b u t i o n of the casebearer  on the foliage„on the number of insects per f a s c i c l e . is f a i r l y stable, small, reduces labour of recording  This unit of f o l i a g e in the f i e l d or  laboratory, speeds calculation and contains eggs, a l l instars of larvae, and pupae. This unit closely s a t i s f i e s the six c r i t e r i a for selection of the sampling unit laid down by Morris  ( 1 9 5 5 ) , namely:  (a)  A l l units must have an equal chance of selection  (b)  The sample unit must be stable  - 36 -  (c)  The proportion of insect population using the sample unit as a habitat must remain constant  (d)  The sample unit should be reasonably small so that enough units can be examined on a given plot to provide an adequate estimate of sampling variance  (e)  The sample unit should lend i t s e l f to estimates of absolute population  (f)  An important practical consideration is the ease of col 1ect ion.  Timing of Sampling  S ign i f i cance:  After the sampling unit is selected, i t is necessary to  decide how sampling should be timed  in relation to l i f e history of the  casebearer, i t s pattern of mortality and location of stages. a time interval  is selected in which the insect is on oviposition s i t e s ,  feeding s i t e s , or i t is in a resting stage. that is hidden disturbed  Generally,  This is preferable to a stage  (e.g. in the needle mines), r e l a t i v e l y mobile, or e a s i l y  (e.g. the moths).  Sampli ng Intervals: Egg  - at the time of completion of oviposition and commencement of hatching  Larva (L^) - at the time of diapause and needle  f a l l when  larvae are firmly attached to the branch Larva (L^) - at the commencement of spring a c t i v i t y Pupa  - just before emergence or after emergence. timing is important  in assessing rates of  mortality by parasites.  Here  -  Fig. 6.  a, b, c.  37  -  L i f e stages of the larch casebearer sampled.  a.  Needle f a s c i c l e s showing spring feeding damage to needle tips and pupa.  b.  Eggs on adventitious new needles. Courtesy of The P a c i f i c Forest Research Centre.  c.  Overwintering cases on dormant larch twig.  - ho -  The calendar dates of sampling may vary widely from year to year. ' Therefore, the actual dates of sampling are dictated by prevailing rates of insect development. may  Determinants  be obtained by spot sampling or by indices such  of these rates, as  developmental  curves or by phenology, such as degree days above a certain threshold temperature.  Field  Procedures  Fifteen western sampling,  larch trees were selected for casebearer  12 trees at Thrums (Fig. 7 '  Each tree was  ) and 3 trees at Sheep Creek.  numbered and tagged for future reference.  These,trees  were located with respect to position in the stand as follows: Interior stand trees (Nos. Edge trees (Nos.  1-4) Thrums (Fig. 7)  5"8)  Open grown trees (Nos.  9-12)  In clusters of trees (Nos. 13 — 15)  )  Sheep Creek  The few, scattered, 'open grown', trees were located along pathways into the stand. Increasing egg deposition sometimes occurs on trees along edges of stand openings.  This is a function of (a) host discovery which  is probably most evident when insect populations spread  into new areas,  and/or (b) more favourable microhabitat with more l i g h t , differences in quantity and quality of foliage, etc. on the exposed side.  It is  therefore suspected that edge trees tend to receive more eggs than do trees in the interior of the stand.  - h] -  The same trees were sampled New  through one insect generation.  trees were selected for the 1975 egg c o l l e c t i o n .  Crown levels:  The crown of each sample tree was v i s u a l l y divided  horizontally into 3 levels of equal v e r t i c a l (Fig. 8) ) and v e r t i c a l l y  length (lower, mid, upper  into 2 halves (exposed and shaded).  Two  c l a s s i f i c a t i o n s of branches, r e l a t i v e to the degree of exposure to sunlight, were recognized: (a)  branches f u l l y exposed to l i g h t , such as, branches from isolated or open grown trees or from the sides of trees facing an opening, and  (b)  branches shaded by nearby adjacent trees, such as, in the i n t e r i o r of a dense stand;  It was assumed that differences in l i g h t intensity affect variation in number of f a s c i c l e s and number of insects per f a s c i c l e among the branches. Branches:  To obtain information on the d i s t r i b u t i o n of the casebearer  on the branch, two whole branches were removed from each crown l e v e l , one from the exposed and one from the shaded side of the tree. cardinal points were approximately:  The  south for the exposed, and north  for the shaded branches on stand edge and i n t e r i o r stand trees. Each entire branch was measured and cut into 3 equal sections. From each section two 6-inch  (15 cm)  lengths were cut at random, one  from the main branch, and one from a lateral branch (Fig. 8 ) .  This  gave s i x 6-inch lengths per branch or t h i r t y - s i x 6-inch samples per tree. The sample branch was  removed by extendable pole-pruners with  clamp attachments f o r the lowering of the branch with a minimum risk of dislodging insects from the sample. A 2k foot ( 7 - 3 m) extension ladder was also used for reaching the t a l l e r trees.  -  kl  -  Larch Stand  c  ( ( (  Opening  r  Right-of-way for wire-line  -To Castlegar  Figure 7.  Highway No. 3  -> To Nelson  Diagram showing r e l a t i v e positions of sample trees at Thrums, B.C.  F i g u r e 8.  a.  Division of tree crown v e r t i c a l l y and h o r i z o n t a l l y .  b.  Sample branch showing  branch sections  ( 6 ) selected.  -  44  -  Each sample unit was placed in a separate p l a s t i c bag inches (12.7  5x9  x 23 cm), labelled, tied with "twistums", and transported  to a laboratory at the University of B r i t i s h Columbia for cold storage at 5 C and counting or rearing of the various stages of the larch casebearer. Collections by two persons from the 15 sample trees from two areas took 34 -  man-days, depending on insect stage and weather.  t r i p from laboratory to the f i e l d took 34 -  A return  days.  Collection dates, insect stages and sample sizes: 1.  Pupal stage:  2.  Egg stage:  3.  Initial  1 5 1 6 May 1 9 7 4 , 540 subsamples from 15 trees -  1 1 - 1 2 July 1974,  larval stage:  324 subsamples 9 trees  2 - 3 November 1 9 7 4 , 432 subsamples  from 12 trees 4.  Final  larval stage:  24-25 April  1 9 7 5 , 540 subsamples, from  15 trees 5.  Pupal stage:  10-11 June 1 9 7 5 , 540 subsamples from 15 trees  6.  Egg stage: 2 2 - 2 3 July 1 9 7 5 , 288 subsamples from 8 trees.  Collections for the egg stage were taken in the f i e l d  from  15 trees, but the high density of eggs and the low v a r i a b i l i t y of egg counts allowed the use of fewer trees to obtain the.required level of prec i s ion.  -  45  -  Assessing the Tree  The same branch samples taken for insect counts were u t i l i z e d to determine the d i s t r i b u t i o n of f a s c i c l e s within the branch.  As already  described the f o l i a t e d whole branch was divided into 3 equal lengths and one 6-inch  (15 cm) section taken from the main axis, and one from a  lateral of each of the 3 portions.  It was  required to know how the  f a s c i c l e s were distributed among the crown levels because there were differences in insect population density among the 3 crown levels. Accordingly, the total number of f a s c i c l e s was  recorded for each  15cm -  sect ion.  Sampling for Morphological Characteristics of Branches  The following c h a r a c t e r i s t i c s were studied by subsampling: (a)  Number of needles per f a s c i c l e .  This was measured by  counting the number of needles on 10 f a s c i c l e s per branch selected at random from the branch samples that were i n i t i a l l y used for insect population counts on June 1975, from trees Nos. 1, 3, 5, 6 and 7 . (b) nearest  The longest needle per f a s c i c l e was measured to the  mm.  Distribution of Foliage and Shoots  The proportional d i s t r i b u t i o n of f o l i a g e , needle f a s c i c l e s , and shoots within the crown, and variations within various crown types, or locations in the stand were investigated for four crown types in accordance with Ives'  (1959)  c l a s s i f i c a t i o n for tamarack  in eastern Canada, namely:  -  ke  -  Crown Type  Character i st ic  Ful1 crown  taper uniformly from bottom to top of tree e.g. Open grown trees  Irregular  a preponderance of branches on one side of the tree at d i f f e r e n t crown levels, e.g. tree along margin of stand  S1ender  trees with dead primary branches replaced by short branches originating from adventitious growth on the main stem; rare in western stands  High  mainly in dense stands, considerable natural pruning from branch suppression e.g. interior stand trees.  Defoliation . Measurements  The assessment of damage to the trees in relation to d e f o l i a t i o n necessitates recognition of, and allowance f o r , several determinant variables.  These comprise:  f o l i a g e age, location of foliage in the crown,  time of d e f o l i a t i o n and stage of leaf development.  Accordingly, these  variables were measured on the 15 sample trees. The larch casebearer feeds by mining the peripheral 1/3 or 1/2 of any needle and only occasionally the whole needle.  The most noticeable  and e f f e c t i v e damage occurs in early spring at the time of needle growth. Therefore, June when larval feeding ceases, is probably the best time to estimate d e f o l i a t i o n .  Rating Defoliation  Each 6-inch (15 cm) rating as follows:  sample was given a numerical  defoliation  -  (1)  kl  -  For pupal samples 0 - Negligible - no v i s i b l e damage 2 - Light - up to 25% of foliage damaged  26-50% of foliage damaged 5)"75% of foliage damaged  k -  Moderate -  6-  Heavy -  10 - Severe - over 75% of foliage damaged (2)  For egg samples The estimate of d e f o l i a t i o n was improved (a)  to give:  proportion of the number of needles per f a s c i c l e mined per sample unit (= Quantity).  (b)  proportion of the volume of needles per f a s c i c l e rendered non-functional by the insect per sample (= Volume). 0 = No Defoliation 1 = Negligible 2 = 5-15% 3 = 16-25%  h  = 26-35%  5 = 36-50% 6 = 51-60% 7 = 61-75% 8 = 76-85% 9 = 86-95% 10 = over 95% 11 = dead spurs  Insect Counts and Accessory Information  A l l data were recorded on f i e l d data sheets in a format d i r e c t l y convertible to automatic data processing (Appendix 1 3 ) . _  -  48  -  General Information, a l l insect stages.  A l l data sheets included the  following pertinent information: Tree No.^date of c o l l e c t i o n , area, crown class, crown l e v e l , exposure, and branch section.  For each 6-inch  (15 cm) branch sample the number of f a s c i c l e s or l i v e spurs in winter, dead spurs, and bases of side shoots were recorded. Pupal samples:  Number of pupae on each 6-inch (15  counted and d e f o l i a t i o n rating recorded.  cm) sample were  Records were kept also of moth  and parasite emergence (Appendix 1). Egg samples:  Sampling was carried out at about the time of completion  of egg hatching.  Eggs were counted and records kept of unhatched  empty chorions, and ecluded eggs.  eggs,  The condition of eggs were distinguished  as follows: Unhatched  eggs - yellow-orange content w i l l hatch eventually - translucent white and  (live)  'collapsed', or discolored  (dead)  Empty chorions - transparent chorions, contents extracted probably by mites or Ecluded or  hemipterous predators  - grayish egg chorions often f i l l e d with frass giving a  hatched eggs  white green color i n i t i a l l y  and darkening to a reddish  brown color. The d e f o l i a t i o n rating, number of eggs per f a s c i c l e , portion of needle on which egg was found (tip,  mid and base), conditions of needle  (sound or damaged), needle surface (upper or lower) on which egg was  found,  were also recorded. Counts were made by examination of needles under a dissection microscope, by rotating one f a s c i c l e of needles at a time. task was completed most of the needles f e l l  Before the  from the f a s c i c l e during the  rotation process, and had to be examined individually.  The procedure was  -  ks  -  tedious and time-consuming with the exception when only total egg counts were made.  However, time could be saved by having an assistant do the  record i ng.  Overwintering Larval Samples  This was the easiest and quickest insect stage to count, as most of the abscising needles had f a l l e n o f f during c o l l e c t i o n .  Counts were  made of larvae on spu-rs, base of spurs, at nodes on bark and among the lichens when present, for each 15cm _  branch sample.  Checking Insect Counts  Counts were checked to reduce percentage of insects missed, and depended on the r e l a t i v e concealment and size of each stage of the insect.  In the prewinter and postwinter larval stages the insects were  readily seen and checking was easy.  After i n i t i a l counts the pupae were  placed in individual p;lastic bags or v i a l s f o r rearing and a second count was made after emergence of adults, the differences between counts were negligible. For eggs, which are small and e a s i l y missed, thorough checks were necessary.  This was carried out through several re-examinations of  the needles under the microscope or other magnifier.  If the needles remained  on the short shoot during examination for eggs, there was a 10 percent difference in egg counts between consecutive checks. However, when the needles dried out and f e l l - o f f the branches up to 20 percent difference in egg counts between consecutive checks occurred.  - 50 Rearing Methods  Most of the rearing experiments were intended to yield information on casebearer or parasite emergence and therefore mortality of  larvae or pupae on the d i f f e r e n t 15cm -  various strata in the tree crown.  branch samples taken from  As most parasites emerges as adults  during the pupal stage of the casebearer, i t was generally found more satisfactory to rear mature larvae or pupae collected  in the f i e l d ,  rather than e a r l i e r stage larvae. After i n i t i a l counting and removal of other insect species, each 15-cm  section  was  placed in 5 x 9 inch (13 x 23 cm) p l a s t i c bags  and tied at the neck with twistums. temperature at 20-23C  (68-75F) and  Rearing was carried out at room at  60-75%  r e l a t i v e humidity.  About 10% of the pupae collected were removed from the branch samples and reared as follows: (a)  In shell v i a l s 50 x 15 mm and 160 x 15 mm  stoppered with cotton  wool or cork, and (b)  In gelatine capsules 20 x 5  mm.  The other pupae were reared on the branch sections in 5 x 9 inch (13 x 23 p l a s t i c bags in which the 15"cm  samples were o r i g i n a l l y placed when collected  i n the f i e l d .  Experimental  Observations  Behavioural a c t i v i t i e s were observed of  in the f i e l d at the time  larval feeding as a casebearer, and at the time of adult emergence  and mating  cm)  (11-12 June 1974 and 15 June 1975).  -  51  o  Figure 9.  Collection and rearing bag with 15 cm _  branch section.  - 52 -  ANALYSIS OF DATA  The s t a t i s t i c a l  techniques used f o r analyses of the data on  each l i f e stage of the insect are b r i e f l y defined.  Their relevance and  limitations in describing population d i s t r i b u t i o n and v a r i a b i l i t y , and in estimating overall populations parameters are outlined. Frequency Distribution The frequency d i s t r i b u t i o n of counts formed an important aspect of the quantitative studies of insect populations and received attention in the s t a t i s t i c a l  analysis.  Theoretical d i s t r i b u t i o n s have been f i t t e d to the data for one or both of the following reasons: 1.  To find a transformation in order to use the normal theory for s t a t i s t i c a l analysis, such as the analysis of variance ( i t does not matter  i f the form of d i s t r i b u t i o n f i t t e d  is p a r t i c u l a r l y  accurate (McGuire, et_ a_j_. 1957) ) . 2.  To relate observed or spread  data to some theory of population growth  (requiring forms of d i s t r i b u t i o n s that are biological  s i g n i f i c a n t , such as the negative binomial  (Anscombe, 1 9 5 0 ) ,  the Poisson (Skellam, 1952, McGuire, et a 1.  1957)-and Neyman  type-A (Neyman,  1939).  Determination of the theoretical d i s t r i b u t i o n which best f i t s the set of observed values, and the chi-square test for goodness of f i t , required a modified form of the computer program written by Kozak and Munro (1963) at the University of B r i t i s h Columbia. This fitted  computer program  the observed data to the four probabi1ity d i s t r i b u t i o n s commonly  -  recognized  in forest sampling;  negative binomial.  53  -  the normal, Poisson, binomial and  The parameters calculated from the data were:  the mean, standard deviation, number of frequency classes, the value of probability P for the binomial d i s t r i b u t i o n , and the constants k and P^,  for the negative binomial d i s t r i b u t i o n .  In i t s original form  the program accepted a maximum of 2 0 frequency classes and this had to be increased to take 3 0 or more frequency classes for the present study.  F i t t i n g the Distributions  The counts were analysed the number of 6-inch ( 1 5 c m )  in a frequency d i s t r i b u t i o n showing  branch sections containing 0 - 0 . 5 ,  0.5 0.1, -  0.1-0.15, ...insects per f a s c i c l e for a given l i f e stage. If the insect is randomly distributed over the sampling  universe,  the d i s t r i b u t i o n of insect per unit w i l l approximate a Poisson series where the variance (S ) of the population equals the mean (x). appearance of a frequency d i s t r i b u t i o n may of experimental  design.  The  merely r e f l e c t an a r t i f a c t  For example, as the size of sample unit and/or  population density increase, the zero values tend to disappear, and d i s t r i b u t i o n appears to approximate a normal bell-shaped curve.  the  Often  there are more zeros and high values than expected, and as a result 2  —  S >x.  This departure from randomness is referred to as "overdispersion". The negative binomial  is the most useful d i s t r i b u t i o n that has  been applied for overdispersed insect counts.  This d i s t r i b u t i o n is  described by 2 parameters, the mean and the exponent k_ which is a measure of aggregation. Generally values of k_ are in the region of 1 or 2 .  As they  - 54 -  become larger ( i . e . as S the Poisson.  approaches x) the d i s t r i b u t i o n approaches  Fractional values of j< lead into the logarithmic series.  The value of J< may be computed by several methods (Anscombe, 1949,  1950;  Southwood  B l i s s and Fisher, 1953;  I966;  Katti and Gurland  Debauche 1962;  1962).  Legay 1963 in  Only one method is presented  here:  -2  where S  = variance  m E i=l  m E (f.x.)' VN i=l N-l  where E = the sum of f.= frequency of the i " ^ class 1  m = number of frequency classes th x.= mid-point of the i class (e.g. no. of insects) N = no. of observations (Ef.) 1 The e f f i c i e n c y of this estimate of J< is r e l i a b l e only at low density  popu1 at ions.  Transformations  It is often necessary to transform observations before analys so as to more nearly s a t i s f y the assumptions of the usual techniques.  statistical  The normal or Gaussian d i s t r i b u t i o n is not of interest as  - 55 -  means of deciding dispersion of insect population.  Its importance  l i e s in the fact that for most s t a t i s t i c a l methods the d i s t r i b u t i o n must be normal and possess the associated properties that the variance is independent of the mean, and 1965).  i t s components additive (Southwood,  In order to meet the assumptions of analysis of variance, the  data are transformed.  Thereby the observed  data are replaced by a function  whose d i s t r i b u t i o n is such that i t normalizes  the data or s t a b i l i z e s the  variance. Different kinds of transformation have been devised for the purpose, the a p p l i c a b i l i t y of which depends on the p e c u l i a r i t i e s of the data.  Among the more usual transformations tried are:  (a)  7x,  (b)  Jx + 1/2 Bartlett  (c)  Log^^  (d)  X, P  the square root transformation (Bartlett, 1936) (1936)  (X + 1 ) , the logarithmic transformation (Williams, 1964)  Taylor power law (Taylor 1 9 6 1 ,  1965)  Taylor's Power Law  The d i s t r i b u t i o n of individuals in natural populations is such 2  that the variance (S ) is not independent of the mean (m).  Taylor  (1961)  2  from the examination  of several sets of samples found  the S  appears  related to the nn as they tend to increase together when plotted and to obey a simple power law. 2 b S = am c  where a and b are c h a r a c t e r i s t i c s of the population in question.  - 56 -  The and  s e r i e s o f means a n d v a r i a n c e s  £ was o b t a i n e d  necessary  t o c a l c u l a t e a_  from s e t s o f samples from d i f f e r e n t  trees.  The  2 values  o f m and S  log s c a l e .  c a l c u l a t e d f r o m t h e raw d a t a  a r e p l o t t e d on a l o g /  T h e v a l u e o f a_ a n d b_ a r e c o m p u t e d by l i n e a r  regression in  l o g a r i thms.  2 log S = l o g a + b l o g m w h e r e l o g a_ a n d b_ a r e i n t e r c e p t a n d r e g r e s s i o n c o e f f i c i e n t r e s p e c t i v e l y . 2 Taylor rise  (1961) h a s shown t h a t t h e r e l a t i o n s h i p S  t o a system o f t r a n s f o r m a t i o n s  stabilizing  count  from t h e a p p r o p r i a t e  gives variance  function f(m):  f(m) From t h i s ,  derived  = a m  = Q_jm"  b/2  the quantity  dm  ( T a y l o r , 1965)  t o be a n a l y z e d  (X) by t h e e x p o n e n t i a l Y =  X  (Y) i s t r a n s f o r m e d  from the o r i g i n a l  expression:  P  where X = t h e o r i g i n a l  number,  Y = the transformed  v a l u e and  p = (1 - 1/2b)  The  If p = 0  a logarithmic transformation  I f p = 0.5  square roots a r e a p p r o p r i a t e ;  I f p =-0.5  r e c i p r o c a l s q u a r e r o o t s a r e r e q u i r e d ; and  I f p =-1.0  r e c i p r o c a l s a r e t o be u s e d  exponential  expression  o f a d d i n g a "C" c o n s t a n t  Y. = ( X . + C ) I  I  was u s e d  in this  P  be u s e d ;  (Southwood,  study  t o the v a r i a b l e before  should  but w i t h  raising  1966).  the modification  i t t o t h e power o f p:  -  57  -  This constant is needed when zero values are frequent in the data to be transformed and  i t could be between 0.5 and 2.0.  values the constant of 1.0 was  After trying several  found to be the best for the present  study. The use of transformations may of means, which may  lead to problems in the comparison  be based on d i f f e r e n t transformations.  Justification  exists therefore for not transforming the data unless i t seriously violates the conditions necessary for the analysis of variance (LeRoux and Reimer, 1959)was  For comparison, in this study analysis of variance  also computed on the untransformed  data.  The adequacy of a transformation in s t a b i l i z i n g the variance can be tested graphically or by c a l c u l a t i n g the correlation c o e f f i c i e n t of the two terms (means and variances) (Harcourt, 1961b, I 9 6 5 ) ; and also by Bartlett's test for homogeneity of variances.  Analysis of Variance or ' F '  Test  The analysis of variance is used advantageously  in research  where quantitative data are measured, and permits determination of the spatial and temporal insect density. squares  £ (x-x)  factors which exert a s i g n i f i c a n t effect upon  It is the process used for partitioning the sum of into components which are thought  d i f f e r i n g causal circumstances.  to be related to  The objective is to test the hypothesis  that a number of population means are equal.  Therefore, the  procedure  is one of determining how much of the variation in the observations is  - 58 -  due to population differences, and how much to random  variability.  Comparison of the contribution of these 2 kinds of variations allows the determination of the importance of population differences. If the assumptions underlying the s t a t i s t i c a l not f u l f i l l e d ,  the test of significance w i l l  techniques are  be affected.  Four assumptions are usually necessary for the analysis of variance (Piatt and G r i f f i t h s , 1.  1964):  The experimental errors must be independent, may be f u l f i l l e d by assigning treatments at random.  2.  The samples are from normally distributed populations, i f non normal can usually be r e c t i f i e d  3.  by transformation.  Variances within each treatment are equal, as the error variance in the analysis is a pooled error and each treatment contributes to i t .  4.  Treatment and environmental  effects must be additive, i.e. the  treatment and replication effects in a randomized block design must not interact. It should be noted that i t is not certain that a l l of the assumptions are met, even with transformation.  Quenouille (1950) observed  that, in t-test and the variance ratio test, i t is usually more important to meet assumptions of (2) and (3) only.  Regression and Correlation  Calculations of regression and correlation were applied for describing the s t a t i s t i c a l to determine  relationship between means and variances,  i f data transformation was necessary.  There are several  - 59 -  simple methods of studying  relationships among variables  (the scatter  diagram, freehand trends, and the method of selected points).  However,  for s t a t i s t i c a l analysis, the method of least squares for f i t t i n g regression  lines is most r e l i a b l e .  Regression offers a useful approach to  the study of simultaneous variation of 2 (or more) variables. regression  With  the m variables are d i f f e r e n t i a t e d into (m-1) independent  variables and one dependent variable.  The problem is to find the values of  a_ and J), in the equation:  Y = a + b„X + b X + 2 1 2 2  + bX mm  which minimizes the sum of the squared deviations  between predicted and  A  observed values of Y where; Y is the predicted value of Y, a_ is the intercept which fixes to position of the l i n e , and b. are the regression c o e f f i c i e n t s . The correlation c o e f f i c i e n t (r) measures the degree of linear association between 2 variables.  That i s , i t gives an evaluation of the  mutual relationship between 2 variables even when no cause-and-effeet relationship is known. and  The d e f o l i a t i o n rating was recorded for the pupal  egg stages and these were correlated with the number of insects (eggs)  per f a s c i c l e .  The c o r r e l a t i o n c o e f f i c i e n t can vary from -1 to +1.  A  c o e f f i c i e n t of 0 indicates no linear correlation and a c o e f f i c i e n t of 1 a perfect linear c o r r e l a t i o n . of external  When variables are j o i n t l y affected because  influences, c o r r e l a t i o n o f f e r s a logical approach to the  analysis of data.  In correlation analysis, random pairs of observations  are assumed and information 2 variables.  is obtained about a j o i n t relationship between  While in regression analysis only the dependent (Y) variable  is assumed to be random, and regression almost implies a cause-and-effeet relationship.  - 60 -  Coefficient of Determination ( r ^ ) : This c o e f f i c i e n t is a measure of the amount of v a r i a t i o n in Y a t t r i b u t a b l e to the independent var iable X.  The Number of Samples  The number of samples required for estimating  the mean densities  of insect stages depends on the degree of precision or accuracy required, the amount of interbranch variance that exists within trees, the number of branches sampled per tree and trees in the:.stand.  the amount of variance that exists between  Several complicated  methods for calculating sample  size have been used, among which are the following f i v e examples: (a)  Where sampling is necessary at two  levels, e.g. between and  within  trees, the number of units (Nt) that need to be sampled at the higher  level e.g.  tree (LeRoux and  from Southwood 1965) is given (S s/N ) + Nt = § (XD) 2  Reimer, 1959; Harcourt 1961a  by:  S P2  2  where N  s  2 = the number of samples within habitat unit (trees), S^ = variance 2  within the habitat unit (within tree variance), Sp unit (= intertree variance), x data and given  = variance between habitat  = mean per sample (calculated from transformed  in this form), and D = the required size of the  standard  error expressed as a decimal f r a c t i o n (0.1 normally) of the mean.  - 61 -  If the dispersion of the population has been found to be well  (b)  described by the negative binomial the desired number of samples is given by:  N  =  1/x + 1/k  where x = mean, k = the dispersion parameter of the negative binomial, D = the required size of the standard error expressed as a decimal fraction of the mean (Rojas,  To find the combinations  1964).  of Nt (No. of trees) and N  sample units per tree) that w i l l provide equal sampling  (1955)  g  (No. of  precision, Morris  used:  Nt =  2 2 St . N + Sc s (Sy)  2  . N  2 where St = the variance component of trees, 2 Sc  = the variance component for sample units (branch) within trees,  Sy  = the standard error of the mean, set at various prescribed percentage of the mean.  (c)  Sampling can be based on the measurement of the frequency of occurrence of an organism, e.g. the frequency of occurrence of casebearers on a f a s c i c l e (Oakland,  1953;  Henson,  1954).  - 62 -  An e s t i m a t e o f s a m p l e  s i z e c a n be made by f i r s t  value o f the p r o b a b i l i t y found The  o f o c c u r r e n c e o f an a t t r i b u t e  t h a t 35% o f t h e f a s c i c l e s  number o f s a m p l e s  obtaining  have c a s e b e a r e r s  an a p p r o x i m a t e  (p) e . g . i f i t  this probability  is  i s 0.35.  (N) i s g i v e n b y :  J. N =  1  P  D  q  2  w h e r e t = a q u a n t i t y d e p e n d i n g on t h e no. o f s a m p l e s a n d d e g r e e o f c o n f i d e n c e , and i s o b t a i n e d p = the p r o b a b i l i t y q =  from  t-tables,  of occurrence,  1-p,  D = required  size of the half  confidence  interval  about  the estimated  mean. (d)  I f i t i s found t h a t in  the d i f f e r e n t  with (e)  probability  the f a s c i c l e s are distributed  parts of the.habitat, proportional  they should  to the variances  F i n a l l y , when t h e number o f t r e e s p e r p l o t very  large,  the required  s t a g e c a n be c a l c u l a t e d MS  N t - -  w h e r e Nt = r e q u i r e d = desired (not  be s a m p l e d  (Henson,  t o be s a m p l e d i s  number o f t r e e s t o be s a m p l e d (from ana 1 y s i s  1954).  f o r each  of variance) as:  •  M  D  D  t  differently  2  sample  size  standard  (no. o f t r e e s ) ,  error  o f t h e mean i n t h e u n i t s  in percent),  1  = levels within  r  = samples  each  tree,  (branches) w i t h i n  each  MS = v a r i a n c e c o m p o n e n t s f o r t r e e s .  level,  of observations  - 63 -  Allocation of Optimum Sampling  Effort  The findings in this study are integrated into a plan for future sampling of the larch casebearer.  It deals with how  to take  the samples, how many are needed, and where these samples should be taken to get the most precise estimates with the available resources. The following questions were asked: 1.  What precision was  obtained?  2.  What intensity of sampling w i l l be needed in future work to obtain a precision of 10 or 20 per cent of the mean?  3-  How  should these samples be distributed on a tree crown and  among the trees on a plot? h.  How many trees are needed per plot?  Data Preparation and Analysis Procedures  Larch casebearer data were punched on IBM cards and analyzed on the University of B r i t i s h Columbia IBM 370 Model 168 electronic computer, using several programs including the following: UBC  MFAV  Analysis of Variance/Covariance.  This program computes  an analysis of variance for a wide variety of designs.  MFAV can also  perform Duncan's Multiple Range Test or test contrasts on the means for a particular source of v a r i a t i o n .  Degrees of freedom, sums of squares,  means of squares, variance ratios (F-test) and means of variables are tabulated, involving a maximum of 9 factors with up to 50 levels in each factor.  Provision is made for any model, equal or unequal  and selection of any error term desired.  replications  -  UBC  (Forestry)  Fortran  MREG  IV for IBM  7040  modified for the IBM  64 -  Multiple Regression. Data Processing  370/168  System.  This MREG program is in  System (Kozak and Smith  1965)  A series of separate tabular values  is calculated and a maximum of 70 variables may be analyzed at one time.  The  Basic Unit of Sampling  The  basic unit of sampling was the 6-inch  (15 cm) branch section and  development of the sampling technique was based on analyses of inter- and intra-tree v a r i a b i l i t y of the number of insects per fascicle/15~cm  branch  sect ion (q). This is a compound variable as both the numbers of insects (Y) and  the numbers of f a s c i c l e s (x) per 15 cm. branch section are variables. The  The  individual observations are ratios of two variables  (q. = Y./x.).  ratio estimator used was the "means-of-ratios" estimator (q = Z r  In general,  n  q./n). 1  the sampling mean and variance of r a t i o estimators are biased,  the bias, however, is usually n e g l i g i b l e for large samples. of population  Ratio estimates  means or totals may or may not be more "stable" (less variable)  than the corresponding values obtained by simple expansion ( i . e . by computing Y = E Y./n as opposed to Y = q x x). The v a r i a b i l i t y of Y r e l a t i v e to s i r r n  that of Y  s  w i l l depend on the sign and size of the correlation c o e f f i c i e n t  between Y. and x. and the c o e f f i c i e n t of variation of these variables. 1  1  The use of ratio estimators in this study did not a f f e c t the s t a t i s t i c a l analyses, but would a f f e c t the c a l c u l a t i o n of total number of insects and f a s c i c l e s per tree.  - 65 RESULTS AND DISCUSSION  Frequency  Distributions  The d i s t r i b u t i o n of the larch casebearer in the volume of the tree crown could be in the form of gradients from periphery to center.  from top to bottom and  These gradients are mainly the result of  behaviour towards l i g h t , gravity, temperature, moisture or available sites for feeding or oviposition.  However, within this overall gradient  the insect may be distributed either randomly or contagiously. Several ways of determining the spatial d i s t r i b u t i o n patterns of the larch casebearer were carried out, namely, frequency d i s t r i b u t i o n s and chi-square tests, the r a t i o of the variance to the mean, k_ parameter of the negative binomial and b_ of Taylor power law. The larch casebearer counts were summarized by insect stages  (15cm) branch sections within the density class 0-0.05, 0.05-6.10, 0.10-0.15, ... etc. casebearers per f a s c i c l e  showing the number of 6-inch l i m i t s of "(Table 1).  The frequency d i s t r i b u t i o n s of the number of insects  (except  egg stage) per f a s c i c l e did not follow the normal d i s t r i b u t i o n , but were strongly  skewed toward  the l e f t  (Figs. 10,  11).  Observed data f i t t e d the negative binomial d i s t r i b u t i o n for larval and pupal stages and approached egg stage (Appendix k, Tables 1-6).  the normal d i s t r i b u t i o n for the In the process of f i t t i n g the negative  binomial, any "extra" modes were assumed to represent random v a r i a t i o n .  - 66 -  Table 1.  Frequency d i s t r i b u t i o n s of numbers of insects (larch casebearer) per f a s c i c l e for the l i f e stages sampled.  Class Limi ts  Pupa  1974  Number of Insects per Larva Egg 1974 1975  1974  3  Fascicle Larva, 1975 *  Pupa  1975  .05  255  19  17  103  204  316  • 05-  .10  79  4  7  42  78  74  .10-  .15  58  17  9  49  68  47  .15-  .20  10  7  31  33  25  .20-  • 25  30 33  10  9  31  29  17  • 30  23  16  17  34  22  14  • 30-  .35  14  20  11  24  19  10  .35"  .40  9  10  11  14  3  .40-  • 45  11  13  13  12  14  8  9  .45-  • 50  8  10  8  13  6  4  .50-  .55  13  27  18  9  16  5  • 55-  .60  0  20  7  8  6  4  .60-  • 65  2  9  10  7  7  2  .65-  • 70  0  18  8  5  2  2  • 70-  .75  1  10  10  4  3  0  .75-  .80  0  15  10  6  2  3  .80-  .85  0  12  14  1  1  0  .85-  • 90  0  8  6  1  2  0  .90-  • 95  2  11  7  4  1  0  3  0  0  0  o.oo-  • 25-  • 95-  1.00  0  1  1 .00-  1.05  1  16  13  10  10  1  1.05-  1.10  0  4  8  2  9  1  1.10-  1.15  0  4  10  1  0  0  1.15-  1.20  0  3  3  2  0  0  1 .20-  1  0  3  2  2  0  1  1.25-  1.30  0  5  4  2  0  0  1.30-  1.35  1  2  8  0  0  0  1.35-  1 .40  0  2  2  2  0  0  1.40-  1.45  0  1  4  1  0  0  1.45-  1.50  0  24  33  1 1  0  2  324  288  432  540  540  .25  Total:  540  0/ -  (a)  Pupae ~]h l  2 5 2 2 0 0  2 0 6  o c  <u  Z3 cr <D 1 0 0  1 2 0  51+  1 0  I.I.I 0  1  2  3  1  +  5  6  7  8  9  0.  No. pupae per 15-cm branch  0 2 5  0 . 2 2 5  0 . U 2 5  No. pupae per f a s c i c l e  301  <> b  2 5 6  Pupae  Si.  '75  2 0 3 2 0 3  u c rj  15«*  CT <U  l_  U .  1 0 5  1 0 3  5<»  0.  Figure 10.  0 2 5  0 . 2 2 5  0.1(25  Frequency d i s t r i b u t i o n of Insects per f a s c i c l e and per 15-cm branch section,  a) Pupae ~Jk\ b) Pupae '75. x  0 . 5 7 5  - 68 -  Eggs per f a s c i c l e  1(7  1974  r  40  3 0  >O  20  c  cr 10 5  0.05  0.45  0.85  Eggs per 15cm  1.55  1.2 5  branch section  -  27  20  1  r  r  1  , '' 0  1  1  2  1  1  1  it  .  1  1  6  1  1  1  8  1  .  1  I ' ' 1 I .  1 0 1 2  14  1 6 1 8  Class Interval  F i gure  11.  Frequency d i s t r i b u t i o n of eggs per f a s c i c l e and per 15-cm  branch section.  - 69 -  The Variance - Mean Ratio  2 The variance (S ) of the number of insects per f a s c i c l e calculated for each tree sampled was  related to the mean (x) , as in a  Poisson form of d i s t r i b u t i o n (Fig. 12a).  However, in most trees larch  casebearer densities exceeded variance, and more tree samples were found in both t a i l s of the frequency polygon than are expected  in a Poisson  2 d i s t r i b u t i o n (where the S  = x). 2  The variance/mean (S /x) ratios (an Index of Dispersion) of the independent variables (egg, larvae, and pupae per f a s c i c l e ) were low, indicating the uniformity of spatial pattern. This was  due to the fact  that the total number of insects per 15 cm. branch section was divided -  by the number of f a s c i c l e s on that section.  When the 15 cm. branch section -  was made the sample unit (numbers of insects per branch section), the variance/mean ratios of a l l stages of the casebearer were high, indicating the aggregative nature of the data. For the egg stage (1975) the variance and mean per tree was largely independent, and the d i s t r i b u t i o n approached normality. confirmed when variance was  plotted over the mean (Fig. 12b).  This was The  counts  for the egg stage in 197** apparently f i t t e d the negative binomial but approached the normal d i s t r i b u t i o n s as indicated by the chi-square tests. 'k' as an Index of Aggregation  The frequency d i s t r i b u t i o n s of the various stages of the larch casebearer were aggregated  or clumped among trees as indicated by j< of the  negative binomial d i s t r i b u t i o n (Table 2).  The value of k as a measure of  -  a.  70  Pupa ' 7 5  -  Variance on Mean  0 . 1 4 0  0 . 1 1 2  0 . 0 8 4  0 . 0 5 7  0 . 0 2 9 1-  0 . 0 2 9  0 . 0 5 3  _L  0 . 0 7 6  0 . 0 9 9  _1_  0 . 1 2 3  0 . 1 4 6  r-^r-= 0 . 94 5  r—J= 1 , 0 50  b. Egg ' 7 5 0 . 4 4 9  0 . 3 9 0  0 . 3 32r  0 . 274f  0 . 2 1 6t  *-= 0 . 52 3  Figure 12.  >  s-jr^s 0 •. 6 2 8  r - i ^ r 0 .7 34  0 , 8 39  The relationship between mean number of insects per f a s c i c l e and variance,  a) Pupa lk; l  b) Egg.  -  71  -  dispersion can range from zero where aggregation is extreme, to i n f i n i t y which defines a purely random d i s t r i b u t i o n of counts. In practice however, any large value of k_ indicates an approach to randomness (Waters,  1959).  The higher j< values ( 3 . 3 ) for the egg stages at low population density r e f l e c t s an i n i t i a l  random tendency  in new infestations.  lower Rvalues for larvae and pupae r e f l e c t a later aggregative  The tendency  even in light infestations, and the retention of this c h a r a c t e r i s t i c due to mutual attraction at the particular times of c o l l e c t i o n (Table 3 ) . Possible causes w i l l be noted subsequently  Table 2.  in this manuscript.  Effect of development of larch casebearer during a single generation on estimate of the parameter k_ and _b for i t s immature stages, Thrums, B.C.  1974-75-  Date  Stage Recorded  May 1974  Pupa  July 1974  Egg  Nov.  1974  April  1975  Larva (L ) Fall Larva (L^) Spring  June  1975  Pupa  July  1975  Egg  Mean density per f a s c i c l e  0.1218 0.6365 0.3H5 0.1855 0.1067 0.7132  k_  Value : Of b^  0.450 3.347 0.630 0.475 0.257 3-245  1.3577 1.1873 1.8149 1.8570 1.7190 0.4944  Unfortunately, k is somewhat unstable, as i t frequently increases with the mean.  Therefore, i t is advisable to s t r a t i f y f i e l d data wherever possible  in order to improve estimation of j< (Harcourt, 1 9 6 3 ) -  - 72 Table 3-  Estimates of J< of the negative binomial for each insect stage per f a s c i c l e and per 15 cm. branch section. -  Unit of  Egg  Egg  Larva^  Larva^  Pupa  Pupa  1974  1975  1974  1975  1974  1975  0.629 3.347  0.713 0.300 3-245 0.630  O.I85 0.475  0.122 0.101 0.450 0.258  7.856 2.5H  8.535 2.584  3-104 1.835 1.069 0.891  1.378 1.093 0.720 0.507  Observation  Fasc icle/15 cm. -  branch_ sect ion  x  k.  15cm. -  brancjn sect ion  x k  It is evident that the observational unit (Table 3 ) .  Rvalues are affected by size of the  This additional source of heterogeneity  may be attributed to the d i f f e r e n t number of f a s c i c l e s per unit  branch  length at the various locations on the branch, and the aggregation habits of the prewinter and postwinter larvae and the pupae. When the negative binomial series was f i t t e d to counts of casebearer per f a s c i c l e per 15 cm branch section, and counts per 15""cm. branch section, -  there were no s i g n i f i c a n t differences between observed and expected values.  ;  l t is concluded  that the negative binomial gives an adequate  ;  description of the frequency d i s t r i b u t i o n of counts of prewinter and postwinter larvae and pupae of the larch casebearer. Taylor (1961 and 1965) contends  that the s t a t i s t i c b_ is a true  "index of aggregation" and that a_ depends largely on sampling or computing characteristics.  The index of aggregation b_ is a true population s t a t i s t i c  describing an i n t r i n s i c graduation from:  property of the organisms with a continuous  - 73 near regular (b<l) through random (b = 1) to highly aggregated (b>l) In the present study the aggregative tendency of postwinter larvae (L^)and pupae appeared to be similar as the R v a l u e s for larvae^ and pupae  (1975)  did not d i f f e r s i g n i f i c a n t l y (Table  4).  The  t-tests calculated as per example below,'indicated that the 'b' values for all  l i f e stages sampled with the exception of the egg stage were s i g n i f i c a n t l y  1.  greater than  Thi s result i  indicated high aggregation in a l l  larch  casebearer 1 ife stages sampled except ieggs. Table 4 .  Regression and correlation of log variance on log mean for a l l stages of the larch casebearer. Regress ion  Var iable  (1974) Egg (1974)  -0.433 -0.502 0.306 0.102 0.197 -0.490  Larva L^ Larva L,  4 Pupa (1975) Egg (1975)  Example:  on log x  b  a  Pupa  log r  1 .358 1 .205 2.351 1.857 1.711 0.494  O.96O  0.816 0.906 0.906 0.927 0.414  P  = 1 -1/2b 0.321 0.398 -0.175 0.0715 0.1445  0.753  Calculation of t-test for prewinter larvae. t =  where b = regression c o e f f i c i e n t b  b G = 1, the number to be compared with and SE, = standard error of b b  _ 1.857 - 1 _ .8570 * ~ 0.2408 .2408  =  . „  q  -  From t-table with 13 df (f - 2 ) ,  74  -  t = 3 - 0 1 2 at p = 0.01  so that  b = 1.85 d i f f e r s s i g n i f i c a n t l y from 1. The egg counts for  197**  showed a diminished aggregative  tendency and approached a random d i s t r i b u t i o n as b_was only s l i g h t l y s i g n i f i c a n t l y greater than 1; whereas eggs collected  in 1975  tended  toward a regular d i s t r i b u t i o n . According to Taylor (1965)  the power law appears to hold good  down to low densities (x>l) in material examined. populations aggregated  This implies that  at low density tend to become regular when density  increases, or vice versa.  According to Taylor the law may  eventually, or perhaps the concept of aggregation  (S  break down  > x) is inappropriate  at these low levels.  Discussion on  Distribution  The larval and pupal data f i t t e d the negative binomial, and  the  value k gave a measure of dispersion. The smaller the value of k, the greater the extent of aggregation, whereas a large value (over about 8) would have indicated a Poisson (random) d i s t r i b u t i o n .  The d i s t r i b u t i o n of  the egg stage in 1974 more closely f i t t e d the negative binomial  distribution  than the normal d i s t r i b u t i o n , but in 1975 i t followed the normal d i s tribution more closely. defoliation  This was  in 1974 which resulted  probably due to the much heavier in the departure of suitable needle  f a s c i c l e s on branches from the normal d i s t r i b u t i o n the section on f o l i a g e ) .  (discussion under  -  75  -  The aggregation recognized by the negative binomial was  due  partly to the active aggregation by the larval stages prior to and after winter dormancy, and just prior to pupation, and partly to some heterogeneity of the environment  such as d i s t r i b u t i o n of needle f a s c i c l e s , microclimate  and natural enemies. The s u i t a b i l i t y of the negative binomial in describing frequency d i s t r i b u t i o n s of larch casebearers does not mean that aggregation is in any sense explained.  As the negative binomial has been deduced from a  number of widely contrasting hypotheses  regarding the mechanism of  dispersal, some examples are given by Waters and Henson The negative binomial d i s t r i b u t i o n may  (1959)•  have arisen through  the aggregation tendency of prewinter larvae, postwinter larvae and pupae, or through s t a t i s t i c a l a r t i f a c t s . caused by preferential  Biological aggregation was  responses to external stimuli, inter or intra-  s p e c i f i c interactions, or reproductive behaviour as discussed below. S t a t i s t i c a l a r t i f a c t s may a r i s e through sample unit size, shape and density (Waters and Henson, 1 9 5 9 ) or by combining or non-random d i s t r i b u t i o n s ( B l i s s , 1 9 5 8 ) .  samples from a number of random Accordingly, the explanations  for aggregation in the various insect: stages are discussed below. Egg Aggregation.  Aggregation could be due to a behavioural  cause, as the females tended to deposit a number of single eggs close to one another on the same needle or needle f a s c i c l e . up to h eggs, and f a s c i c l e s up to 8 eggs in 1 9 7 4 .  Some needles contained A l t e r n a t i v e l y , aggre-  gation might be owing to the heterogeneity of the environment,  in which  only certain areas are suitable for oviposition, as the females concentrated their egg deposition on undamaged needles of old growth.  -  76  -  However, when d e f o l i a t i o n is light or negligible eggs are deposited singly and scattered on f a s c i c l e s over the entire branch: Larval Aggregation.  The prewinter larvae are highly aggre-  gated as they s e t t l e down for winter dormancy.  Shoot spurs contained  up to 9 larvae per spur in moderate population densities. The postwinter larvae were s t i l l  aggregated after winter  mortality and one week of insect a c t i v i t y .  The larvae spend the f i r s t  week molting and occasionally enlarging their cases.  Later on they  become more dispersed as feeding progresses. Pupal Aggregation.  Although the larch trees were l i g h t l y  to moderately defoliated, between 70 and 8S% of the f a s c i c l e s contained no pupae.  It is apparent that there'was either heavy mortality or  aggregation in the late larval stage.  Although pupal numbers were low  on most trees, mature larvae were s u f f i c i e n t l y attracted to each other prior to pupation, so that, there was occasionally more than one pupae per needle f a s c i c l e .  Up to 5 pupae per f a s c i c l e were observed.  Transformation of Data  Before s t a t i s t i c a l  tests, such as the analysis of variance,  could be applied to the data of insect stages, the highly skewed frequency d i s t r i b u t i o n s had to be transformed to meet the assumptions This was  necessary because the frequency  of the tests.  d i s t r i b u t i o n s of the number of  insects per f a s c i c l e , the variable to be analyzed, did not follow the normal d i s t r i b u t i o n (except eggs 1975) .  Secondly, transformation was  -  77 -  required because the variance of the number of insects per f a s c i c l e calculated for each tree sampled was highly related to the mean. The most obvious departure from normality was the strong correlation between the variance and the mean (Table 5 ) . The larger the absolute value of r_, the closer the points w i l l f i t the l i n e .  Table 5-  The correlation between mean and variance for the l i f e stages of larch casebearer.  Correlation c o e f f i c i e n t s (r)  Stage  Untransformed  Pupae 1 9 7 4  0.969 *  Egg  0.816V:  1974  Larvae 1 9 7 4  0.946 *  Larvae 1 9 7 5  0.688*  Pupae 1 9 7 5  O.685*  Egg 1 9 7 5  0 . 2 0 3 ns  *  Significant  (P < 0 . 0 1 )  (P > 0 . 0 5 )  ns = not s i g n i f i c a n t  The exponential transformation x  P  suggested  by Taylor (1961) ,  where p is the Taylor power for transforming aggregated  biological data,  is the most applicable in these situations, but with the modification of adding a "C" constant to the variable before raising i t to the power of JD:  Y. = (X. + C ) . P  This constant  is needed when zero values are  frequent in the data to be transformed and i t could 2.0.  be between 0 . 5 and  The constant of 1 . 0 was found to be the best f i t in the present  study.  In the above transformation p_ is defined by the relationship between the mean and the variance.  The values of p for the present study were:  -  78  -  1974  1975  Pupa  0.3538  (0.3)  0.1445  (0.1)  Egg  0.4063  (0.4)  0.7530  (0.7)  Larva  0.0925  (0.1)  0.0715  (0.1)  The above transformation eliminated the dependency of the variance on the mean and also  tended to normalize the frequency  distributions.  79  -  FACTORS AFFECTING THE  Source of Variation in Population  -  DISTRIBUTION OF CASEBEARER  Estimate  The s i g n i f i c a n t variables  (branch section, level and  generally had very high F-ratios and  their consistent  most analyses (Appendix *t, Tables 6, 7 and that these three variables contributed variation of eggs, larvae and within trees.  Population  8)  trees)  significance in  substantiated  the fact  most to the estimated  density  pupae of the larch casebearer among or  means are expressed in terms of the o r i g i n a l  variates. Inter-Tree  Variation For a l l three l i f e stages the number of insects per  was  s i g n i f i c a n t l y d i f f e r e n t (0.01  so that the total  other trees and discussed  probability level) from tree-to-tree,  insect population  This difference could be due  fascicle  sampled was  d i f f e r e n t from tree-to-tree.  to some trees having more f a s c i c l e s than  therefore fewer insects per f a s c i c l e , but w i l l  be  under the section on f o l i a g e . The average number of insects per f a s c i c l e was  s l i g h t l y greater on  edge trees than on the interior or open grown trees, but this difference originated from one  tree only  postwinter larvae and  (tree No.  (tree No.  5)  8)  for prewinter larvae  for pupae collected in 197*+ -  and Open grown  trees appeared to have more eggs than trees in the other stand positions in both 197*t and  1975  within the groups was between categories  (Appendix k,  Table 9 ) .  The  tree-to-tree v a r i a t i o n  more s i g n i f i c a n t for a l l stages than the v a r i a t i o n  of trees related to position in the stand ( i . e . i n t e r i o r  stand trees, edge trees, open grown trees, and c l u s t e r s ) .  the  - 80 Intra-Tree  Variation 1.  Crown Level Variation The three crown levels, namely the lower, mid and upper  third, showed s t a t i s t i c a l l y s i g n i f i c a n t differences in insect densities for all  three  insect stages (Fig. 13 and Appendix 4, Tables 6, 7, 8 ) . For  pupal stage in 1974 the number of insects per f a s c i c l e was  the  significantly  (P = 0.01) higher in the rhid crown level than in the upper crown l e v e l , but no differences was was  found between the lower and  the upper l e v e l s .  no s i g n i f i c a n t differences between levels for the pupae in For eggs in both 1974 and  (P = 0.01) higher in the mid and trees; but no difference was  1975 the density was  There  1975. significantly  upper levels than in the lower level on a l l  found between the mid and upper l e v e l s . Pooled  data for a l l trees showed the highest density on the upper crown l e v e l . For the prewinter larvae, the number of insects per was  significantly  (P = 0.01) higher in the mid  l e v e l , but no difference was  all  trees, density  in the mid  when the 15 cm.branch was -  crown level than in the lower  found between the mid and  appeared to be similar to the egg  fascicle  upper l e v e l s . This  stage, but when the densities were pooled for  level was  higher than in the upper l e v e l . However,  taken as the sampling unit, instead of the f a s c i c l e ,  the relationship between levels was  s i m i l a r to that of the egg  stage.  For the postwinter or spring larvae the number of insect per f a s c i c l e was  s i g n i f i c a n t l y higher in the lower crown level than in the  mid and upper levels when a l l the trees were pooled. to the fact that a l l the edge trees in the stand had higher numbers (especially tree No. and  This was  attributable  significantly  (P = 0.01)  8) in the lower level than in the mid  upper levels; whereas on the average, the i n t e r i o r stand and open  grown trees had levels.  s l i g h t l y more insects on the average in the upper and  There were no differences between the mid and  the trees were pooled.  mid  upper levels When  -  81  -  These conclus ions can be drawn from the comparison densities per crown level (Figs. 14a,  15a,  of the average  (Fig. 13) but they are not true for every tree  16a and Appendix 4 , Tables 10, 11).  In fact, there  was  a s i g n i f i c a n t interaction between tree and crown level for the larvae (prewinter and postwinter), The trend for the postwinter  indicating a d i f f e r e n t trend from tree to tree. larvae seems to be affected by position of  trees in the stand as explained  above.  While for a prewinter larvae, the  lower level had the least density on 8 of 12 trees. For the egg and pupal stages the interaction between a l l trees and crown levels was one  not s i g n i f i c a n t , but the trends were d i f f e r e n t from  tree to the other.  However, for eggs, 8 of 9 trees in 1 9 7 4 , and 7 or 8  in 1 9 7 5 had fewer eggs per f a s c i c l e in the lower than in the mid or upper 1evels. 2.  Exposed and Shaded Branches This is more important at mid and  low levels of interior  trees or edge trees rather than open grown trees. and postwinter  stand  The number of prewinter  larvae, pupae (1974) and eggs (1975) did not, on the average,  d i f f e r s i g n i f i c a n t l y between the exposed and shaded branches when the data for a l l trees were pooled.  However, densities were s l i g h t l y higher on  exposed branches for larvae and pupae eggs (1975) on  7  per f a s c i c l e was  of the  9  trees.  significantly  (1974),  and on shaded branches for  The number of eggs  (P = 0.01)  on the shaded ones (Fig. 13, Appendix 4  (1974)  and pupae  (1975)  higher on exposed branches than Tables 6 , 8 ) .  However, the tree-  to-tree v a r i a t i o n between the exposed and shaded branches (Figs. 14, 16 and Appendix 4 , Tables 1 2 , 1 3 )  the  15,  indicates that the trend toward higher  or lower numbers :between the exposed or shaded branches, respectively, is not consistent from one  tree to another.  - 82 -  \  , Lower  Fig. 13.  •  ,_  Mid  Upper  Number of insects per f a s c i c l e by Crown Position.  Figure A.  ig. .14.  Figure B.  Number of pupae per f a s c i c l e ; a) by tree and-CTOwn-posi-t-ion-;-" b) by exposure, branch position arid tree,  1974.  Fig.  15. . _i_  Number o f eggs p e r f a s c i c l e ; •.  _  -.-—  a)  by t r e e and c r o w n p o s i t i o n ;  — b - ) — b y — e x p o s u r e , -br-aneh--pos-i-t-ion-and - t r e e , ' 1 974.  0. tl  ,  ,  a) \by . tree .and crown position; b) by exposure, branch position and tree, 1974.  - 86 -  -  3.  87  -  Main or Side Branches S i g n i f i c a n t l y more pupae in 1974 and  1 9 7 5 per f a s c i c l e  occurred on the side branches than on the main branches,  but s i g n i f i c a n t l y  more overwintering larvae per f a s c i c l e occurred on the main branches than on the side branches.  In 1 9 7 4 the egg population was,  on the average,  higher on the main branches, while the postwinter larvae were more abundant on side branches,  but these differences were not s i g n i f i c a n t  s t a t i s t i c a l l y on the two types of branches (Fig. 17, and Appendix 4 , Tables 14, 15).  But in 1 9 7 5 . the number of eggs per f a s c i c l e was  significa  higher on the main branches than on the side branches. However, notwithstanding  the overall trends, i t would be a  mistake to draw a general conclusion from the above results, because the trend changes from tree-to-tree (Figs. 14b,  1 5 b , 16b and Appendix 4 ,  Table 12), and for the prewinter larval stage, i t changes for the three different crown levels (Appendix 4 , Table 9 ) • 4.  Horizontal Crown Position Fig. 18, Appendix 4 , Tables 16, 17, 18, 1 9 , 20 and 21  indicate the trend of number of insects per f a s c i c l e by horizontal crown position (stem to periphery) for the three l i f e stages sampled. In general, i t can be concluded  that the population density close to  the stem is low for a l l stages, and parts of the crown.  increases for the mid and outer  However, this trend is inconsistent from tree-to-  tree (Appendix 4 , Tables 16, 1 7 , 18, 19, 20 and 21).  The 1 9 7 5 egg  population was more evenly distributed through the horizontal crown position, possibly due to light d e f o l i a t i o n which resulted in the a v a i l a b i l i t y of sound needles throughout  the  branches.  - 88 -  No. of i nsects/ fasc i c l e  * Eggs  0.7  0.6 Eggs Side branch 0-5  I Main branch  O.k Main branch  ' Larvae, L.  0.3  • * Larvae, L.  0.2 • ' Pupae  Side branch  0.1  Pupae  Side branch  Main branch  0.0  I nner  Mid  Outer  Sections from Stem to Outer Crown  Fig. 18.  Number of insects per f a s c i c l e by horizontal crown position.  -  89  -  DISTRIBUTION OF THE POPULATION BY LIFE STAGES  The aspects of natural within-tree d i s t r i b u t i o n of the larch casebearer investigated were: (a)  d i s t r i b u t i o n of eggs among certain categories of foliage;  (b)  horizontal d i s t r i b u t i o n of different  insect stages on the  branch i.e. from stem to periphery; (c)  v e r t i c a l d i s t r i b u t i o n of d i f f e r e n t stages.  The Egg Stage  Distribution of Eggs  The location of  5274  eggs was observed,  six-inch branch samples taken from  9  trees in  2650  1974,  and  eggs on 2624  324  eggs on  2 8 8 six-inch branch samples taken from 8 trees in 1 9 7 5 -  Current Growth vs. Adventitious Foliage vs. Old Growth Foliage  Development of current shoots was severely inhibited by insect attack on the tree or by other environmental factors.  Its peripheral  location probably increases the chances of egg laying females alighting on i t .  However, needle f a s c i c l e s tended to receive r e l a t i v e l y more eggs  in comparison to current shoots in the proportion of about 7 5 and 2 5 percent.  -  90  -  Percentage of Eggs on: Current growth needles ... Less than 2 5 % per 1 inch branch length Old growth needles (fascicles) ... More than 7 5 % per 1 inch branch length. The ratio of current to old needles per inch branch length was Oviposition sites might be linked to:  1:3.  (l) needle shape, there being a greater  width at the apical third of needles in f a s c i c l e s at oviposition time; (2)  single needles on current shoots are not yet f u l l y developed, and needles  in f a s c i c l e s on older growth o f f e r a better standing platform for ovipositing fema1es. New adventitious needles produced after severe d e f o l i a t i o n in early spring appeared one tree was  to be the preferred oviposition s i t e s .  However, only  found during this study with new needles in late spring.  Compared with two neighbouring trees without adventitious needles, there were 3 - 5 times more eggs on f a s c i c l e s of adventitious needles than on old needle f a s c i c l e s .  This preference for new needles was  supported by  the Forest Insect and Disease Survey Rangers and colour s l i d e s (Fig. 6 b ) borrowed from the P a c i f i c Forest Research Centre, V i c t o r i a , B r i t i s h Columb i a. Also, sound needles were preferred to damaged needles.  In 1974  when d e f o l i a t i o n was moderate 8 9 . 6 % of the eggs were l a i d on sound needles and 1 0 . 4 % on damaged needles (Table 6 ) .  In 1975 d e f o l i a t i o n was  light  and therefore more sound needles were a v a i l a b l e for oviposition and only 5 . 2 % of the eggs were laid on damaged needles.  It is also possible  that the ratio of 1 0 . 4 / 5 - 2 merely r e f l e c t the r a t i o of damaged needles in 1 9 7 4  and  1975.  -  Table 6 .  Tree No.  91  -  Egg d i s t r i b u t i o n by needle condition and on needle surface - 1 9 7 * * .  Total Eggs  Need 1e Sound Damaged No.  Needle Surface Lower Upper No.  2  215  203  12  5.6  209  6  2.8  3  218  208  10  4.6  204  14  6.4  4  222  184  34  15.6  203  15  6.9  5  173  148  35  19.0  172  11  6.0  6  224  191  33  14.7  211  13  5.8  7  355  339  16  4.0  338  17  4.7  9  300  296  4  1 -3  296  4  1.3  10  438  387  51  12.0  420  18  4.0  11  505  424  81  16.0  454  41  8.0  2650  2374  276  10.4  2511  139  5-2  Total  Egg Placement on the Needle Surface  Often more than one egg (up to 7 or more in severe infestation) is deposited on a needle surface, so that larval competition in the mines occurs.  In 1 9 7 4 , only 2 . 9 percent of the total egg counts were deposited  as more than one per needle  (Table 7 ) .  In the 1 9 7 4 c o l l e c t i o n s 3 . 2 percent of the eggs were on the upper and 9 6 . 8 percent on the lower needle surface. surface the incubation period is passed  On the lower needle  in saturated humidity as  95~100  -  92  -  percent of the stomata on the average leaf are found on the underside and as a l l or most of the transpiration occurs through the stomata, the  insect's eggs are in highly humidified atmosphere (DeLong,  Tabl.e  Distribution of eggs on the needle  7.  Tree  Avg.  No.  Defoliat"  Total Eggs  (1974).  Portiion of Need 1e Apex  Mid  1971).  No. of eggs/needle  Base  1  2  3  4+  2  5  215  198  14  3  203  6  0  0  3  4  218  200  12  6  202  4  0  0  4  6  222  205  11  6  204  9  0  0  5  6  173  149  17  7  167  3  0  0  6  7  224  214  3  7  211  3  1  1  7  4  355  324  13  18  343  6  0  0  9  4  300  298  1  1  269  10  2  1  10  5  438  347  35  56  406  16  0  0  11  6  505  446  32  27  476  13  1  0  2381  138  131  70  7  2  89-9  5.2  4.9  2.6  Average Percentage  2650  0.3  Preference for the apical third of the needle probably originates  from the c h a r a c t e r i s t i c resting position of the adult near  the needle t i p , as 8 9 . 9 percent of the eggs were laid on the apical third  in 1 9 7 4 (Table 7 ) more in 1 9 7 5 -  -  93  -  Vertical Distribution of Eggs  The variation in density along the v e r t i c a l height of the crown is shown in Tables 8 and 9 for 1 9 7 4 and 1 9 7 5 per sample were light to moderate.  The numbers of eggs  The greatest density of eggs in both  years was found in the upper tree crown, with the least density per needle f a s c i c l e in the lower crown.  The percentage d i s t r i b u t i o n of eggs per  f a s c i c l e in the tree crown {25% lower, 35% mid and h0% upper crown levels) was similar for the two years although different trees were sampled. When egg density per 15 cm. branch section were used (Table 9 ) -  the higher density of f a s c i c l e per sample in the upper and mid crown levels were reflected  in the higher d i s t r i b u t i o n of eggs, in the upper crown which  was double that of the lower crown l e v e l .  Horizontal Distribution of Eggs  Differences in egg numbers along branches from periphery to stem is shown in Table 1 0 .  There is a s i g n i f i c a n t difference between the  section near the stem and the mid and outer sections; but no s i g n i f i c a n t difference between mid and outer section for eggs collected  in 1 9 7 4 .  This is due partly to the more concealed situation of the inner branch section which reduces the chance of ovipositing females coming with the f a s c i c l e s in this section.  It is due also to the lower density  of needle f a s c i c l e s on the inner section. was more heavily defoliated  in contact  Furthermore, the inner section  in 1 9 7 4 , and as there was no adventitious needle  growth the number of prefer red. oviposition sites was considerably reduced.  -  Table 8 .  -  Distribution of _C. lar i c e l 1 a eggs per f a s c i c l e by crown levels as collected at Thrums 1 9 7 4 and 1 9 7 5 -  Crown Level  94  1974  No. of eggs/ fasc i c l e  -  1975  % of total eggs  No. of eggs/ fascicle  -  % of total eggs  Lower  0.505  26  0.564  25  Mid  0.662  35  0.792  35  Upper  0.742  39  0.891  40  Total  1.909  2.247  Average  0.636  0.749  Table 9 -  D i str i but ion of C. l a r i c e l l a eggs per 15-cm. branch section by crown levels and years.  Crown Level  1974  No. of eggs/ sect ion  -  • 1975  % of total eggs  No. of eggs/ sect ion  -  % of total eggs  Lower  5-741  23  5-500  20  Mid  8.389  34  10.208  37  Upper  10.463  43  11.771  43  Total  24.593  Average  8.198  27.479 9-15  - 95 In 1975,  actual  d e f o l i a t i o n was light and the d i s t r i b u t i o n  of eggs through the branch tended to be more uniform. branch section  The peripheral  contains s l i g h t l y fewer eggs than the mid and inner  sections due to the inclusion of a few new growth terminals from tree No. 12 on which only 0-3  eggs were l a i d .  Relationship Between Degrees of Defoliation  and Number of Egg per Fascicle  A s i g n i f i c a n t but weak negative correlation was displayed (r =  -0.166 with  322  degrees of freedom) between the number of eggs per  f a s c i c l e and the quantity of d e f o l i a t i o n  (proportion of needles per  f a s c i c l e mined per sample unit) in 1974. correlation was found (r =  -0.242  with  Also, a s i g n i f i c a n t negative  322  degrees of freedom) between  the number of eggs per f a s c i c l e and the volume of d e f o l i a t i o n  (proportion  of needles per f a s c i c l e rendered non-functional by the insect per sample). These two negative correlations adults select results  less defoliated  in stronger correlation  probability  that the  branches for depositing their eggs, which  Although the above correlations (0.01  seem to indicate  between eggs and sound needle f a s c i c l e s . are highly s i g n i f i c a n t  statistically  l e v e l ) , f o r practical purposes, the quantity of  d e f o l i a t i o n explains only  of d e f o l i a t i o n explains  2.75  5.86  2 percent (r =  2  percent (r =  0.0275)  0.0586)  and the volume  of the variation  of the density of eggs. Defoliation defoliation  rating.  On a scale of 1 to 10 the quantity of  (proportion of needles per f a s c i c l e mined per sample unit) was  moderate to severe in the Spring of 1974 sistent differences  (Table 11).  There was no con-  in d e f o l i a t i o n between tree crown levels.  -  Table 10.  96 -  Number of larch casebearer by tree branch type and horizontal crown position per f a s c i c l e per 2-15cm. branch sections. Inner 1/3  Stage  Branch  Section Mid 1/3  Outer 1/3  Pupae 1 9 7 4  0.169  0.184  0.311  Egg  1.035  1.459  1 .326  La rvae^  0.539  0.663  0.668  Larvae,  0.231  0.346  0.500  Pupae 1975  0.114  0.173  0.270  Egg 1975  1.581 *  1.518*  1.396  197 * 1  4  -'' The inner and mid sections had higher counts than the outer section in the upper crown levels.  Table 1 1 .  Defoliation rating by tree, crown level and exposure at time of egg stage, 1 9 7 * * .  Pos i t ion  Defoli at i on  Rat i ng  -  Quanti ty  2  3  h  5  6  7  9  10  11  LL  2  3  3  6  7  k  4  4  4  LS  8  4  4  6  1  6  7  5  6  ML  4  3  9  6  7  5  4  5  6  MS  3  3  7  9  4  4  6  4  6  UL  3  4  8  4  7  h  2  5  6  US  7  h  1  7  8  2  3  5  5  in Crown  Tree l b .  L = 1 owe r, L = exposed,  M = m i d, U = upper crown l e v e l . S = shaded.  - 97 -  Fig. 19.  Four 15 cm _  2, k,  branch sections showing d e f o l i a t i o n  6 and 10.  ratings  -  97a  -  -  98  -  Egg Distribution in Relation to Adult Behaviour  Adult emergence, behaviour and mating were observed in the f i e l d and laboratory.  Moth emergence started b r i s k l y , reaching  a peak on the second or third day.  In the laboratory (temperature  22C and 7 5 % RH), emergence occurred throughout the day with the greatest number emerging at mid-morning.  After a short f l i g h t the adult takes  up i t s c h a r a c t e r i s t i c resting position on the tips of needles.  This  could account for the oviposition of over 8 5 percent of the eggs on the outer 1/3 of the needles. In the f i e l d , f l i g h t a c t i v i t y , mating and oviposition occurred about sundown.  The moths are crepusular and fading daylight is essential  for courtship and eventual mating.  This is evident as i t is d i f f i c u l t  to obtain mating in the laboratory i f the t r a n s i t i o n from l i g h t to dark is made abruptly.  Moths were active in the f i e l d on 14 and 15 July,  and 15 June, 1 9 7 5 , at 6 : 3 0 p.m.  P a c i f i c Standard Time (PST) at about the  time when overhead light intensities dropped to 2 0 0 ft.-candles. a c t i v i t i e s were reached very quickly.  At 7-*00 p.m.,  (Table  Peak  on the second day  after emergence, most of the moths had paired o f f and mated. continued until dark ( 9 = 3 0 p.m.)  1974,  Mating  12).  This indicated a close association between diminishing  light  intensity and a i r temperature (down from 30C to 20C) and the i n c l i n a t i o n of the moths to mate.  When the sun set behindsurrounding mountains and  the a i r temperatures f e l l  rapidly between 6 5 to 70F (18-21C) the stimulus  for mating was triggered.  There was a dramatic change in habit from the  usually observed daytime indifference of one sex toward the other, to one of a t t r a c t i o n , courtship and mating.  -  Table 1 2 .  99  -  Moth a c t i v i t y as observed on 14-15 June 1 9 7 4 at Thrums, B.C.  T i me  Light  Temp.  (PDT)  f t.c.  C  % RH  23C  67  Hum.  Act i v i ty  14 June 6:30 p.m.  200  High a c t i v i t y through the tree crown commencing f i r s t at the base.  7:00  More than half the adults mating on needles.  7:30  L i t t l e or no f l i g h t a c t i v i t y .  7:50  150  L i t t l e act iv i ty.  8:00  Some a c t i v i t y .  8:30  60  9:00  a 1 most dark  Very l i t t l e a c t i v i t y , a c t i v i t y concentrated mainly in the upper level of crown. 22C  9:10  65  Very few moths active in tree tops.  9:30  dark  A l l f l i g h t a c t i v i t y ceased, some moths s t i l l in copu1 at ion.  15 June 5:45  a.m.  14C  2 pairs of moths mating. 2 fema1es in f1ight.  - 100 -  It is assumed that mating on larch is a behavioural adaptation tending to r e s t r i c t the larch casebearer to this plant. Also, when the moths are disturbed during the day they quickly f l u t t e r back to the same branch or to another part of the host tree. Emergence from the egg is d i r e c t l y through the portion of the chorion attached to the needle into the leaf mesophyl1. the f i r s t and second  This r e s t r i c t s  instar larva to one needle with limited movement  as a leaf-miner.  The Larval  Stage  Larvae Prior to Winter Dormancy  Emergence from eggs is followed by limited movement of early stage larvae.  Eggs and f i r s t  needle on which the egg was  instar larvae are found exclusively on the  laid.  The second  instar larva usually  in the same needle, but occasionally, the larva may f i r s t needle-mine to establish i t s e l f  remain  transfer from the  in other needles, especially when  the egg is deposited on a damaged needle, or the larva is crowded in the mine. The third  instar larva or case-bearing stage is capable of  limited movement, and feeds on a number of needles (8 needles according to Eidmann^1965) prior to hibernation. Therefore, i t is the third  instar  larvae that were sampled for information on the d i s t r i b u t i o n of prewinter larvae at the time of dormancy.  -  101 -  Spring or Postwinter Larvae  A c t i v i t y of the postwinter larvae depended on the course of warming up of the weather in spring. wandering around at about mid April  At Thrums, the larvae began  in 1974 and 1975, at approximately  the same time as the larch needles started to f l u s h .  Feeding is usually  delayed for about a week and commences when the needles are 6-8mm in length. Sampling f o r larvae April  in early spring was carried out on 24-25  1 9 7 5 when larval wanderings had already commenced.  Larval Variation Between Trees  The number of prewinter and postwinter larvae per f a s c i c l e was s i g n i f i c a n t l y d i f f e r e n t ( 0 . 0 5 level) between trees.  The averages showed  s l i g h t l y more larvae per f a s c i c l e on the edge trees than on the interior stand or open grown trees, but this difference originated from one tree only  (tree No. 8 ) .  The tree-to-tree variation within the edge trees was  more s i g n i f i c a n t than within the other stand position (Table of this difference was due to tree No. 8 which had a very high  1 3 ) . Most population,  but was 1ocated in a d i f f e r e n t part of the stand and in mixture with other tree species.  Vertical Variation in the Tree Crown  The number of larvae per f a s c i c l e was s i g n i f i c a n t l y d i f f e r e n t between crown levels, but the significance of interaction between trees and crown levels ( 0 . 0 5 probability level) for the postwinter indicated that the differences were not consistent.  larvae  For the prewinter  -  Table 1 3 .  Tree Number  102  -  Average number of larvae per f a s c i c l e and per 15 cm. branch section by tree and stand position. _  Prewinter Larvae per per fascicle branch section  Postwinter Larvae per per fascicle branch section  1  0.414  3-44  0.312  2.14  2  0.338  3-55  0.106  1.25  3  0.203  2.05  0.123  1.06  4  0.233  2.44  0.180  1.72  0.297  2.87  0.180  1.54  5  0.275  1.80  0.282  1.86  6  0.357  2.42  0.199  1.97  7  0.211  2.72  0.189  0.97  8  0.754  10.14  0.513  6.11  Edge  0.399  4.27  0.296  2.73  9  0.399  2.83  0.158  1.39  10  0.251  2.80  0.187  2.28  11  0.147  2.42  0.151  2.72  12  0.155  2.25  0.072  1.19  Open  0.238  2.60  0.142  I.89  Interior  - 103! "  larvae, the population density was  s i g n i f i c a n t l y higher in the mid  leved'. than in the lower l e v e l , but no difference was found between the mid and upper l e v e l s .  The above conclusions can be drawn from  the averages but they were not true for every tree. This variation of larval density in crown levels is due mainly to variation in mortality and to a lesser extent f a s c i c l e v a r i a t i o n in the tree crown.  These are discussed under d i f f e r e n t sections.  Larval  migration from branch to branch is almost n i l in l i g h t and moderate i nfestat ions.  Table 14.  Average No.of casebearers/15 cm.branch -  C rown  Egg L  L  P  E  3  4  75  " 7 5  ( -  section collected 1 9 7 4 .  Levels  Lower  Mid  Upper  5.741  8.389  10.463  2.444  3.542  3.736  (.269)  (.368)  (.298)*  1.7278  1.722  2.139  (.194)  (.171)  (.174)*  0.767  1.211  1.533  (.080)  (.108)  (.091)*  5.500  10.208  11.770  ) = larvae per f a s c i c l e or spur shoot = Higher number of fascicles/6-inch branch than in the mid and lower  levels.  in the upper crown level  -  As  the needles  the prewinter  104 -  had f a l l e n  o f f a t the time o f c o l l e c t i o n o f  l a r v a e , and as t h e l a r v a e a t t a c h  parts o f the branch,  t h e number o f l a r v a e p e r 1 5 c m . b r a n c h -  may be a b e t t e r s a m p l e u n i t f o r t h i s trend  s e t from o v i p o s i t i o n ,  from the lower  themselves t o various  stage.  T h i s would  section  indicate the  namely, t h e i n c r e a s i n g d e n s i t y o f l a r v a e  t o t h e upper crown  level  14 and F i g . 2 0 .  a s shown i n T a b l e  Exposure  The  number o f l a r v a e  was n o t s i g n i f i c a n t l y  different  However, f o r t h e p r e w i n t e r is  significant  differences  side  increased  initially  a t t h e 0.01  with  height  increased  l a r v a e on t h e e x p o s e d level (Table in  f o r prewinter, 15).  This  interaction  probability  15 shows t h a t with  prewinter  and p o s t w i n t e r )  between t h e exposed  larvae  between e x p o s u r e s  Table  (both  and shaded  per f a s c i c l e branches.  b e t w e e n t r e e s and e x p o s u r e s  level.  This  indicates  that  i s not c o n s i s t e n t from t r e e - t o - t r e e . the d i s t r i b u t i o n  o f t h e l a r v a e on t h e shaded  i n t h e t r e e crown, t h i s  sky l i g h t w i t h  height.  could  be a s s o c i a t e d  On t h e a v e r a g e , t h e  s i d e o f t h e t r e e crown were d e n s e s t a t mid-crown and a t t h e l o w e r l e v e l  indicates higher  f o r the postwinter  overwintering  mortality or  larvae predation  t h e mid crown.  Table  15.  Number o f l a r v a e p e r f a s c i c l e e x p o s u r e and crown l e v e l s .  Insect Stage Prewinter  Postwinter  12  Larvae-  Larvae*--  trees  by c a s e b e a r e r  stage,  Crown  Level  Exposure  Lower  Mid  Upper  Exposed Shaded Average  0.301 0.236 0.269  0.429 0.307 0.368  0.277 0.319 0.298  Exposed  0.222  0.206  0.140  Shaded Average  0.165 0.193  0.136 0.171  0.207 0.173  **  15  trees  - 105 -  Lower  Fig. 20.  Mid  Number of casebearer per 15cm _  Upper  branch section by crown levels.  -  106 -  Larval d i s t r i b u t i o n with respect to exposure was  affected  mainly by variations in mortality which appeared, on the average, to be evenly distributed between exposed and shaded branches within  the  same crown level, but d i f f e r e d between crown l e v e l s .  Main and  Side Branches  S i g n i f i c a n t l y more overwintering  larvae per f a s c i c l e  on the main branches than on the side branches. population was  not d i f f e r e n t on the two  Although the  types of branches.  occurred egg  This d i s -  t r i b u t i o n i s a t t r i b u t a b l e mainly to active larval r e d i s t r i b u t i o n and variations in mortality.  Migration  to the firmer, more sheltered main  branches, or mortality due to desiccation on the side branches (to be discussed) is probably the cause. For the postwinter larvae there main and during  side branches.  As shown in Table 16 this is due  to  migration  the f i r s t week of spring a c t i v i t y to the outer third of the main  branch and branch  is no difference between the  to the side branches which contain more f a s c i c l e s per unit  length.  Horizontal  Crown Variation  For the prewinter larvae, there was  a s i g n i f i c a n t difference  between horizontal crown position, with greater numbers being present on the mid-section of the main branches (Table 16).  For the postwinter larvae,  the s i g n i f i c a n t difference in horizontal crown position was larval migration  due  to the  towards outer third of the main branch, which had  greatest numbers, and  the side branches.  the  - 107 -  Table 16.  Average No. of larvae per f a s c i c l e f o r 12 trees at Thrums by horizontal crown position.  Pos i t ion in Stand  Main 1 nner  Branch Mid  S ide Outer  Branch Mid  Inner  Outer  1nter ior L  3  L  4  0.417  0.254  0.393  0. 1 9 4  0.209  0.314  0.140  0.-161  0.237  0.161  0. 166  0.215  0.379  0.584  O.38O  0.179  0.288  0.335  0.103  0.323  0.515  0.218  0.276  0.340  0.304  0.258  0.337  0.143  0.143  0.268  0.050  0.070  0.224  0.084  0.194  0.231  0.367  0.449  0.362  0.172  0.214  0.306  0.098  0.185  0.325  0.154  0.212  0.262  Edge L  3  L  4  Open  S Average  4  = prewinter larva L. = postwinter larva  Comparison of Branch and Branch Tip Samples  As most of the other studies on the casebearer involved samples of the tips of branches or current growth only, branch tips also were sampled for the spring larvae in the 1975 (Table 17)-  - 108  On tips was  the average, the number of  not d i f f e r e n t  Table 1 7 -  from numbers on  f a s c i c l e on  the outer third of the  Larvae per  Position  branch branch.  Branch tips  0.237  0.234  0.224  0.313*  (Trees 1-4)  trees nos.  10-12  Fascicle  Outer 1/3 of branch  Open (Trees 9"12)  *  larvae per  Comparison of spring larvae per f a s c i c l e by branch tips and by the outer third of branch.  Stand  Interior  -  only  Discussion From the  results  vertical distribution  there is evidence of major changes in  between egg  greatest number of eggs per  and  prewinter larval stages.  f a s c i c l e was  s h i f t of  insect  or greater survival are  population could be the of  larvae, or both.  in the needle-mines and  the  third  limited movements prior to dormancy.  The  found at the upper level of  tree crown while that of the prewinter larvae was The  the  The  instar  at the middle l e v e l .  result of either movement, f i r s t two  larval  instars  larvae are capable of only  Therefore, the  population concentration must be presumed attributable  r e l a t i v e s h i f t of to either  greater  mortality in the upper levels or to differences in the number of spur shoots per  linear unit of twig sample.  the  - 109 -  As shown e a r l i e r , i f the  15cm. branch sample is used as the _  sampling unit instead of the spur, the d i s t r i b u t i o n of the larvae follows that of the egg.  Most of the differences  in larval density  between crown levels appear to correspond to the difference in the number of spur shoots. Reasons Underlying the Distribution of Larvae  The type or condition of the overwintering cases.  Normally in  constructing i t s case, the larva cuts o f f the t i p of the needle.  If the  needle-tip remains attached to the case, or i f the case is the needle-tip, then i t appears that the casebearer was forced to do so because of unfavourable conditions.  Such conditions would be, the drying out of  needles or the lack of readily available needles. It can further be supposed that the higher proportion of cases, with needle-tips or of needle-tips, associated with the overwintering larvae, r e f l e c t s termination of prewinter a c t i v i t i e s e a r l i e r under unfavourable conditions. Table 18 shows the total number and percentage of larvae with cases constructed from needle tips for each sample tree and indicates an overall average of 14 percent of the total cases.  Larvae in these  cases were affected more adversely during the winter than larvae in normal cases and mortality was high. Most needle-tip cases occurred in the upper crown.  The highest  percentage ( 1 8 - 5 1 % ) was on the interior stand trees (nos. 1-4) in the upper crowns and overwintering in or among lichens on branches.  -  Table 18.  110 -  The number and percentage of normal and needle t i p cases by tree for the prewinter larvae 1 9 7 4 .  Tree  Overwintering  Insect  Norma 1 No.  Total  No.  %  Cases Needle-t i p No. %  1  124  102  82.3  22  17.7  2  128  112  87.5  16  12.5  3  74  36  48.7  38  51.3  4  88  55  62.5  33  37.5  5  65  62  95.4  3  4.6  6  87  86  98.9  1  1.1  7  98  93  94.9  5  5.1  8  365  324  88.8  41  11.2  9  102  94  92.2  8  7.8  10  101  86  85.2  15  11  '87  81  93.1  6  6.9  12  81  73  90.2  8  9-8  1400  1204  86.0  196  14.0  Total:  14.8  Larval Behaviour and Distribution Effects  Feeding, Migration and Orientation. migrate to their hibernating s i t e s .  The.prewinter  larvae  The postwinter larvae or spring  larvae wander around during'feeding and occasionally also go to pupation sites.  - I l l  At Thrums, third needles on 25 August 1 9 7 4 . on edge trees.  -  instar larvae were found feeding on No  larvae were found in the needle mines  Denton (1958) found larvae s t i l l  the end of September in Idaho, USA. damaged f o l i a g e was  the  The  a c t i v e l y feeding at  brownish discolouration of  very noticeable at that time.  He stated that as  the older f a s c i c l e s began to fade prior to being shed, the larvae moved out to the needles of new  terminal  shoots that were s t i l l  green.  fore, as many as 3 dozen larvae were found on a single 3~inch new  growth t i p (Denton, 1 9 5 8 ) .  larvae hibernated  This was  not observed  There-  (7.7cm)  in this study as  the  in a variety of s i t e s , such as, under or on lichens on  most main branches, at the base of spurs, and on or under bark of branches. It  is l i k e l y that larvae cease feeding by mid-September in response to  decreasing  photoperiod  either d i r e c t l y or i n d i r e c t l y as a result of the  host tree responding to photoperiod  prior to leaf  fall.  Eidmann (1965) in Sweden, marked prewinter larvae and migration  had  found  taken place in both directions to the periphery of the branch  as well as to the stem, with the majority of larvae migrating one year growth section.  This  toward the  is in agreement with the results of this  study. The prewinter larvae are p o s i t i v e l y phototactic and geotactic shortly before dormancy. Eidmann (1965) showed  negatively  experimentally  using s t i c k s that most of the active larvae migrated upwards. the few  that wandered downwards covered a greater distance.  However, Therefore,  the slope of the substratum seems to influence the d i r e c t i o n of and may  account for migration  migration,  towards the stem on branches at an angle  -  greater  t h a n 90° t o t h e s t e m  towards  t h e main branch Spring  turned, tip. on  a t room t e m p e r a t u r e s  The l a r v a then f a s t e n e d  i f measuring itself  t h e needle u s u a l l y took . about majority  before attaching  can cover c o n s i d e r a b l e experiments.  Loos  (1892)  s p u r was met and  the distance  from t h e needle this  o b s e r v e d marked  f o r more t h a n 3 h o u r s  Even w i t h o u t f e e d i n g  a v e r a g i n g h cm p e r m i n u t e  found c a s e b e a r e r s i n t h e f i e l d  migrating for  normal  distance larvae  larvae  the larvae  i n the laboratory that  i n the f i e l d  and e s t a b l i s h e d  wandered  b e f o r e p u p a t i o n , Eidmann  (1965)  I t was a l s o f o u n d  that  n u t r i e n t d e f i c i e n c y and h u n g e r  ( t h i s may a c c o u n t  and Eidmann  i n 20 m i n s .  stimulated,  f o r some o f t h e d i f f e r e n c e s  b e t w e e n Webb  I965)•  Although the larvae a r e capable o f t r a v e l l i n g i sunlikely that,  travel  a total  in his orientation  1 l a r v a w a n d e r e d 6 3 cm down a 15° s l o p e  1953  Webb  o f b e t w e e n 28 and 32 cms. ( d a i l y a v e r a g e was 4.8 cms)  experiments found  migration  operation  10 m i n u t e s .  l e a s t 5 m e t e r s , a n d saw some t h a t c o v e r e d k cms i n a m i n u t e .  (1953)  it  (22C and  t o t h e n e e d l e and r e s t e d ,  to a needle.  distance  behaviour  i t reached', t h e t i p , t h e n  o f t h e l a r v a e wandered about  themselves  branches.  On a s l o p i n g  a branch  a n d upward a l o n g a n e e d l e u n t i l i t s body'as  side  larval  plants or f r e s h l y c u t larch twigs.  stretching  The  at  O b s e r v a t i o n s on p o s t w i n t e r  s e c t i o n t h e l a r v a moved u p w a r d s u n t i l  then outward  branches) o r  i f l a r v a e a r e on downward s l o p i n g  larvae:  RH) o n p o t t e d  branch  ( i . e . downward s l o p i n g  1 9 7 5 w e r e made i n l a b o r a t o r y  in A p r i l 10%  112 -  in light  beyond a b r a n c h .  and m o d e r a t e  some  i n f e s t a t i o n s , they  distance would  - 113 -  It has been reported young female s t r o b i l i  that the casebearer also feeds on  in the spring (Loos, 1892 and Eidmann, 1 9 6 5 ) .  This was not observed in B r i t i s h Columbia but is worth bearing as i t could affect  in mind  insect counts, d i s t r i b u t i o n or s u r v i v a l .  Loos (1892) mentioned a spring migration of casebearers to the interior of the crown.  In contrast, Webb (1953) described a  tendency to migrate to the t i p of the twig. migration  to the outer  This study showed a  third of the main branch and to the side branches.  Orientation Experiment:  Ten larvae were placed one at a time in a 2 cm  diameter 20 cm long glass tubing, blackened for half i t s length and held at an angle of 30°.  Each larva was placed  in the blackened section on a  s t r i p of paper with a rough surface and the tube stoppered.  The larvae  were stationary for a while and when responding did so slowly, about 2 hours on the average to travel against gravity.  taking  H cm to the lighted section  This indicated that the larvae were more strongly  phototactic than geonegative. Compet i t ion: competition  In the spring insect density becomes important. between larvae.  If more than one larvae per needle (per  spur in the laboratory, Quednau ( 1 9 7 5 ) , personal is present  the larvae w i l l  kill  each other.  communication)  When insects come together  they spin s i l k threads tying their cases together and eventually the cases. preventing  This larval competition overpopulation  There is  leave  gives a density-control factor  and starvation.  This also explains some of the  reasons for the movement of the early spring larvae towards the side branches and the outer third of the main branch where the numbers of needle f a s c i c l e s are dense.  - 114 -  The Pupal Stage  Vertical  Distribution  For the pupal stage in 1974 the number of insects per f a s c i c l e was s i g n i f i c a n t l y higher in the mid crown level than in the upper but no s i g n i f i c a n t difference was found between the lower and levels.  level,  upper  There was no s i g n i f i c a n t difference between crown levels for  the pupae in 1975, but, on the average, the density of pupae was highest in the mid crown l e v e l .  When the 15~cm  branch section was  taken as the  sampling unit instead of the f a s c i c l e , the r e l a t i v e d i s t r i b u t i o n of pupae (1975)  conformed with that of the i n i t i a l egg  (1974)  d i s t r i b u t i o n in the  crown (lower < mid < upper) see Table 19-  Horizontal Crown Position  In general, i t was concluded that the pupal population density on the branch section close to the stem was  the lowest and increased  toward the outer part of the crown (Table 2 0 ) .  However, this trend was  inconsistent from tree-to-tree for the open grown trees. In both years, the average number of pupae per f a s c i c l e and per branch section was 5 0 percent or more, greater for the outer sections of both main and side branches than for the inner sections, as shown in Table 2 0 .  -  Table 19-  115 -  Densities of pupae by crown levels in 1974 and 1 9 7 5 .  Level - 1 9 7 4 Lower  Mid  0.269  0.368  1.233  11.39  Level - 1 9 7 5 Upper  Lower  Mid  Upper  0.298  0.080  0.108  0.091  1.611  1.378  O.767  1.167  1.607  12.21  15-12  11.90  13-73  16.26  Pupae per f a s c i c l e per  15-cm section  Fasc i c l e per 15-cm section  Table 2 0 .  Densities of pupae by horizontal crown position in 1974 and 1 9 7 5 .  Main  Branch  Side Outer  Inner  Branch  Inner  Mid  Mid  Outer  (1)  0.058  0.070  0.121  0.111  0.114  0.190  (2)  0.069  0.082  0.105  0.044  0.091  0.165  (0  0.467  0.689  1 .522  1.37-8  1.544  2.840  (2)  0.400  0.511  1 .289  0.633  1.489  2.700  (1)  9.45  10.93  13.52  13.5  14.07  15.95  (2)  9.93  11.91  14.00  14.63  16.23  16.73  Pupae per  fascicle  per 15-cm  Fasc ic1e per section  (.1) = 1 9 7 4  (2) = 1 9 7 5  - 116 -  Exposure  Although the pooled values of pupal counts per f a s c i c l e on the exposed and shaded sides of trees in 197** were not s t a t i s t i c a l l y  different,  there were more pupae on the shaded side than on the exposed side of the trees.  This was especially so on the edge trees where a strong d i s -  t i n c t i o n in exposure could be made.  The 1975 pupal counts showed the  reverse trend with a s i g n i f i c a n t l y higher number of insects on the exposed branches than on the shaded ones (Table 21). and  Here again, a l l of the edge  i n t e r i o r stand trees showed a marked difference between exposed  and shaded branches (Table 21). The results indicated a switch in the density of pupae from the shaded to the exposed branches or vice versa from year to year.  This  probably occurs when one side is defoliated more than the other and results in few or poor oviposition sites later on in the season.  Factors Affecting Pupal  Distribution  Just before pupation the larva attaches the front-end of i t s case firmly to a needle.  Pupal cases are found mostly in the center of a  needle f a s c i c l e attached to the base of needles, less frequently on the outer portion of needles, and on or among lichens on the branches. They also pupate in other locations on the branches in instances of high population densities or other unfavourable conditions.  -  It appears  117  -  that the casebearer pupates mainly in the  neighbourhood of i t s last feeding place.  However, i t is not uncommon  to find pupae on sections of twigs which have no damaged needle mentioned by Eidmann  Table 21.  (also  1965).  Average No. of pupae per f a s c i c l e by year, position of trees in the stand and exposure. Pupae  Stand  1974  1975  Pos i t ion  Exposed  Shaded  Exposed  1nter ior  0.,106  0. 118  0. 137  0. 101  Edge  0.,161  0. 202  0. 156  0. 067  Open  0.,079  0. 091  0. 110  0. 076  C1usters  0.,043  0. 052  0. 034  0. 030  Average  0.,101  0. 120  0. 114  0. 072  Shaded  The d e f o l i a t i o n rating was recorded for the pupal stage and was correlated index.  with the number of pupae per f a s c i c l e and the d e f o l i a t i o n  The correlation  is s i g n i f i c a n t s t a t i s t i c a l l y , meaning that the  d e f o l i a t i o n p a r a l l e l s the density of pupae, but the relationship explains 2 2 only 7.14 percent (r = 0.0714) and 18.04 percent (r = 0.1814) of variation of the d e f o l i a t i o n  index respectively  in 1 9 7 4 and 1 9 7 5 -  Although pupal populations were low on most trees, i t appears that the larvae had some mutual attraction for each other just before pupation. Up to 5 pupae per f a s c i c l e were observed  in this study.  - 118 -  Larch Foliage  Distribution of Larch Foliage in the Crown  Distribution of the larch casebearer or d e f o l i a t i o n can be misinterpreted or wrongly estimated i f not considered in relation to d i s t r i b u t i o n of f o l i a g e . The d i s t r i b u t i o n of foliage (fascicles per 15~cm branch section) approaches normality as i l l u s t r a t e d from branch samples collected for postwinter larval counts in Appendix 5, F i g . T.  This is confirmed  when variance is plotted over the mean (Appendix 5, Fig. II) which shows the variance and mean largely independent.  It was therefore possible to  apply analysis of variance and other s t a t i s t i c a l  tests on the untransformed  data, of f a s c i c l e counts.  Fasc i cles  1.  Tree-to-Tree Variation For a l l 6 sampling dates in 1974 and 1975 the average number  of f a s c i c l e s per 15~cm branch section was s i g n i f i c a n t l y d i f f e r e n t (0.01 probability level) from tree-to-tree (Tables 22,  23a,  23b and 2 4 ) .  Thus  the total number was d i f f e r e n t from tree-to-tree, but this would also depend on branch length and branches/tree.  However, the averages (Appendix 4,  Table 25) showed that the variation was due to differences between trees within the edge and open grown positions in the stand.  The open grown  trees also had more f a s c i c l e s per branch section than the edge and stand trees.  interior  -  Table  22.  119  -  Analyses of variance of numbers of f a s c i c l e s per 15-cm branch section. May ' 7 4 (pupa)  Source  DF  Mean Sq.  F  June ' 7 5 (pupa) Mean Sq.  F  Tree  T  14  213.5  23.2**  275.4  30.8**  Level  L  2  692.6  75.1**  831.4  93.0**  Exposure  E  1  2.1  Main & Side Branch M  1  1388.8  150.6**  2072.9  Parts, within M  4  264.8  28.7**  240.2  T x L  28  37.2  4. 0 * *  15.8  1.8*  T x E  14  20.0  2.1*  13.6  1.5  T xM  14  10.1  1.0  13.1  1.5  T xP  56  7-4  0.8  17.4  1. 9*-  L x E  2  6.9  0.7  14.0  1.6  L xM  2  3.1  0.3  82.1  9.2**  L xP  8  7-2  0.7  11 . 6  1.3  E xM  1  4.6  0.5  27.6  3.1  E xP  4  25.6  2.8*  7.6  0.8  T x L x E  28  12.1  1.3  12.6  1.4  T x L xM  28  9.1  1.0  21.6  2. 4 * *  T x L xP  112  12.6  1.4*  12.5  1.4*  T x E xM  14  14.3  1.5  14.5  1.6  T x E xP  56  7-5  0.8  12.8  1.4  L x E xM  2  6.6  0.7  4.7  0.5  L x E xP  8  4.8  0.5  13.0  1.5  28  16.2  1.7*  15.8  1.8*  112  9-2  TLEM ERROR TOTAL Significant  P  0.2  1 .2  .1 232.0** 26.9""'  8.9  539  within the 0 . 0 5 l e v e l . ** Significant  within the 0 . 0 1 l e v e l .  -  Table 2 3 a .  120  -  Analyses of variance of numbers of f a s c i c l e s per 15 cm branch section collected for egg counts in 1974 and 1 9 7 5 . -  July 1 9 7 4 DF  Source  Mean Sq.  July 1 9 7 5 F  DF  Mean Sq.  F 8.7**  Tree  T  8  212.2  20.1**  7  88.9  Level  L  2  4 3 1 .1  40.8**  2  304.7  Exposu re  E  1  18.8  1.8  1  16.5  Main & Side Branch M  1  1418.8  I34.3**  1  1148.0  112.4**  P  4  147.7  14.0**  4  51.7  5.1**  T x L  16  28.6  2.7**  14  26.0  2.5**  T x E  8  26.6  2.5*  7  18.1  1.7  T xM  8  40.6  3.8**  7  35-1  3.4**  T x P  32  10.5  1.0  28  12.5  1.2  L x E  2  1 .7  0.2  2  28.4  2.8  L xM  2  5.1  0.5  2  51.9  5.1**  L x P  8  14.4  1.4  8  7.0  0.7  E xM  1  0.2  0.0  1  0.0  0.0  E x P  4  3.6  0.3  4  6.1  0.6  T x L x E  16  17.7  1.7  14  5-9  0.6  T x L xM  16  19.8  1 .9*  14  33.6  T x L x P  64  5.8  0.5  56  9.6  0.9  T x E xM  8  6.1  0.6  7  5-9  0.6  T x E x P  32  7.1  0.7  28  10.0  1.0  L x E xM  2  11.9  1.1  2  14.8  1.4  L x E x P  8  3-5  0.3  8  10.5  1.0  TLEM  16  9.4  0.9  14  7.3  0.7  ERROR  64  10.6  56  10.2  TOTAL  323  Parts, within M  Significant within the 0 . 0 5 level S i g n i f i c a n t within the 0.01 level  287  29.8** 1.6  3.3**  -  Table  121  -  23b. Analyses of variance of f a s c i c l e s per 15"*cm branch section from samples collected for larva and larva Nov.'74  DF  Sou rce  Mean Sq.  Apr.'75  <L > 3  F  DF  Mean Sq.  F  Tree  T  1 1  299.2  43.7**  14  256.0  25.5**  Level  L  2  602.3  88.2**  2  404.5  40.2**  Exposure  E  1  21.3  3.1  1  60.7  Main S Side Branch  M  1  1548.9  226.7**  1  1968.4  195.8**  Parts, within M  P  4  109-0  15-9**  4  236.2  23.5**  T x L  22  27.0  4.0**  28  108.7  10.8**  T x E  1 1  23-3  3.4**  14  14.4  1 .4  T xM  1 1  17.2  2. 5 * *  14  27.6  2.7**  T xP  44  1 1.0  1.6  56  13.9  1.4  L x E  2  0.6  0.1  2  11.9  1 .2  L xM  2  27.9  4.1*  2  4.2  0.4  L xP  8  10.5  1 .5  8  6.1  0.6  E xM  1  0.0  0.0  1  26.2  2.6  E x P  4  11 . 4  1 .7  4  19.8  2.0  6.0*  T x L x E  22  10.4  1.5  28  18.7  1.9*  T x L xM  22  8.5  1 .2  28  13.4  1 .3  T x L xP  88  11.6  1.7**  112  17.6  1.7**  T x E xM  1 1  20.2  2.9**  14  14.1  1.4  T x E xP  44  5-5  0.8  56  8.3  0.8  L x E x M  2  1.9  0.3  2  20.8  2.1  L x E xP  8  6.9  1.0  28  10.0  1.0  TLEM  22  14.0  2.0*  28  12.6  1.3  ERROR  88  6.8  112  10.0  TOTAL  431  539  * S i g n i f i c a n t l y within the 0.05 l e v e l . ** S i g n i f i c a n t l y within the 0.01 l e v e l .  -  2.  122 -  Crown Level Variation There were s i g n i f i c a n t differences (P < 0 . 0 1 ) between the  three crown levels in the number of f a s c i c l e s per branch section (Tables 2 2 , 2 3 a , 2 3 b ) .  The number of f a s c i c l e s per branch section  was s i g n i f i c a n t l y higher in the upper  ( 3 8 % ) than in the mid  ( 3 3 % ) and  lower ( 2 9 % ) levels, and s i g n i f i c a n t l y higher in the mid level than in the lower l e v e l .  The above conclusions can be drawn from the averages  (Table 2k) but they are not true for every tree.  In fact there were  s i g n i f i c a n t interactions between tree and crown level for a l l sampling dates, indicating a different trend from tree-to-tree.  For example,  tree No. 5 was attacked by bark beetles on a few branches, and tree No.15 was heavily attacked by the larch casebearer for a number of years, resulting  in branch die-back and the number of f a s c i c l e s produced varied  greatly.  Also, flowering in the upper and mid crowns and heavier shoot  production in the upper levels affected  the number of f a s c i c l e s per branch  section on some trees, especially the open grown ones.  Table 2k.  Density's percentage d i s t r i b u t i o n of needle f a s c i c l e s per 15~cm branch in 3 crown levels of western larch at Thrums,B.C.  Source 1nterior  *  Edge  *  Open  *  Mid  9.0 30%  10.6 36%  3k%  7.3 26%  8.7 30%  kk%  13-4 33%  15-2 38%  (40.5)  11.7  13.9 37%  (37.2)  32%  11.1  12.9  (33.8)  33%  38%  11.9 29%  CIuster  *  11.6 31%  Average  *  9.9 29%  *  -  Upper  Total  Lower  10.2  12.5  Average dens i t ies of needle f a s c i c l e s per branch section  (29.8)  (28.5)  - 123 -  Crown level variation of f a s c i c l e s in relation to egg depos i t ion:  Most of the v e r t i c a l d i s t r i b u t i o n of the casebearer in the  tree takes place during egg deposition on the needle.  Therefore, egg  counts were compared with f a s c i c l e d i s t r i b u t i o n in the three crown levels (Table 25).  There was a strong correlation between number of f a s c i c l e s  and eggs per crown level.  However, the figures indicate that a much  higher number of eggs are laid  in the upper crown than could be attributed  to the higher density of f a s c i c l e s alone.  It is suggested that the adult  behavioural preference for the more lighted upper level of the tree also plays an important part in the d i s t r i b u t i o n of eggs in the tree crown.  Table 25-  Number of f a s c i c l e s and eggs per 15cm section by year and crown level •  branch  _  No.of fascicles/branch section Year  Lower  Mid  1974  11.39  12.21 15.12  1975  11.90  13-73  Upper  16.26  No.of eggs/branch section Lower  Mid  Upper  5.74  8.39  10.46  5.50  10.21  11.77  Although there are more f a s c i c l e s per 15cm _  branch section in  the upper levels of the crown, the proportion of total foliage by volume or weight in the upper crown level due to the shape of the crown.  is less than the mid and lower levels,  Therefore, total number of insects per  unit area or volume of f o l i a g e would be greater in the upper levels than in the mid or lower levels.  -  3.  124 -  Exposure The number of f a s c i c l e s per 15~cm  branch section did not,  on the average, d i f f e r s i g n i f i c a n t l y between the exposed and shaded branches (Table 2 6 ) .  However the tree-to-tree variation between exposed and shaded  branches indicated that the trend toward higher or lower numbers of f a s c i c l e s per 15-cm was  branch section between exposed or shaded branches, respectively,  not consistent from one tree to another.  This was  attributable mainly  to the open grown trees. A s i g n i f i c a n t l y higher deposition of eggs on the exposed than on the shaded branches bears out observations  that the moths prefer the  more lighted sections of the crown Table 2 7 .  However, the reverse may  true when the exposed side is more heavily defoliated and no new  be  adventitious  needles are formed. 4.  Main and Side Branches Highly s i g n i f i c a n t l y  (P = 0 . 0 1 ) more f a s c i c l e s per branch  section occurred on the side branches ( 5 8 % ) than on the main branches ( 4 2 % ) (Table 2 7 ) .  Table 27 shows that proportionately more eggs were deposited  on the main branches than on the side branch in 5.  197**  and  1975.  Horizontal Crown Position Table 2 8 gives the average number of f a s c i c l e s per branch  section by horizontal crown position from stem to periphery. dates highly s i g n i f i c a n t differences (P = 0 . 0 1 ) occurred  For a l l sampling  in densities of f a s c i c l e s  for a l l horizontal crown positions,with the lowest density close to  the stem, and numbers increased for the mid and outer part of the crown.  This difference was  were considered.  not so pronounced when only side branches  The d i s t r i b u t i o n of f a s c i c l e s did not appear to  125  -  affect  insect density which was  consistently higher on the outer  except eggs which were scattered  Table 2 6 .  -  sections,  over the entire branch (Table 2 8 )  •  Average number of f a s c i c l e s per 15 cm branch sect ion by c o l l e c t i o n period, crown level, exposure and branch type. -  Col 1ect i on Period  Crown Level Lower  Mid  Exposure Upper  Exposed  Branch  Shaded  Ma i n  S i de  1974  May  (P)*  12.2  15.1  13.0  12.8  11.3  14.5  10.4  12.6  14.4  12.7  12.2  10.4  14.6  9.5  11.5  13-6  11.8  11.3  9.6  13.4  9-9  11.1  12.9  11.6  1  9.4  13-2  June (P)  11.9  13.7  16.3  13-9  13.9  11.9  15.9  July (E) .  10.4  12.9  13.8  12.6  12.2  10.4  14.4  Average  10.6  13.3  14.4  12.6  12.2  10.5  14.3  Percent  28.4  33.1  38.5  50.7  49-3  42.3  57.7  July  (E)  Nov.  (L )  11  .4  1975  April  (L ) k  L i f e stage of larch casebearer present at that  1.0  period.  -  Table 2 7 .  -  Average number of f a s c i c l e s and eggs per 15-cm branch section by year, exposure and branch type. Fasc icles/branch sect ion  Eggs/branch section  Exposure  Exposure  Year  Exposed  1974  12.71  1975  126  Shaded  Exposed  Shaded  12.23  9.14  7.25  51%  49%  56%  44%  12.65  12.17  8.99  9-33  51%  49%  49%  51%  Branch  Branch  Year  Main  Side  1974  10.38  14.56  7.46  8.93  41 .6%  58.4%  46%  54%  10.41  14.40  8.85  9.47  42%  58%  48%  52%  1975  Ma i n  S ide  -  Table 2 8 .  127  -  D i str i but ion of insects and appropriate fasc ic1es per 15-cm branch section by horizontal crown pos i t ion. Ma in  Unit/  1 nner  Sect ion  Branch  Side  Branch  Mid  Outer  Inner  Mid  Outer  0.5  0.7  1 .5  1 .4  1 .5  2.8  9.4  10.9  13-5  13.5  14.1  15-9  Hk  4.8  8.0  9.6  7.6  9.8  9-3  Fascicle  8.9  10.1  12.1  13.2  14.1  16.4  2.5  4.0  3.5  2.2  2.7  4.5  8.4  9.4  11.1  12.4  13.2  14.6  0.6  1.2  2.2  1.4  2.2  3.4  8.1  9.4  10.6  11 . 2  13.3  15.0  0.4  0.5  1 .3  0.6  1.5  2.7  9-3  11.9  14.0  14.6  16.2  16.7  8.3  9.9  8.4  10.0  9.4  9.0  10.4  12.2  13.1  14.3  15.5  13.9  16.3  17.6  19.3  20.9  Pupa '7k Fasc i c l e Egg  Larva^ Fasc i c l e Larva,  k  Fasc i cl e Pupa ' 7 5 Fasc i c l e Egg  '75  Fascicle Average Percent  8.9 11.9  Other Factors of Foliage a f f e c t i n g 1nsect Di str i but ion  Foliage variation was also studied under the following headings: number of needles per f a s c i c l e , and needle weight per f a s c i c l e derived by using the regression equation of Ives ( 1 9 5 5 ) > completely  as i t was not possible to obtain  sound (undamaged) needle f a s c i c l e s .  Several factors could  -  128  -  influence the number or weight of needles per f a s c i c l e . were thought important for study include:  Those that  location of the f a s c i c l e  within the branch, location within the v e r t i c a l crown levels, d e f o l i a t i o n and position of trees in the stand.  Number  of Needles per Fascicle  The sizes of f a s c i c l e s varied between different sections of the same branch.  Therefore, 10 f a s c i c l e samples were selected from d i f f e r e n t  parts of the branch for each crown level and exposure, to obtain an average number of needles per f a s c i c l e . the  1975  pupal c o l l e c t i o n  (June  15,  The sampling date was  that of  1975).  On the average, the numbers of needles per f a s c i c l e increase with the height in tree crown levels (Table 2 9 ) , with the edge trees having s l i g h t l y higher numbers per f a s c i c l e than the interior stand trees.  Table 2 9 .  Average number of needles per f a s c i c l e by tree and crown levels. Crown Level  Tree  Lower  Mid  Upper  Range  1  26  31  33  9-45  3  2k  37  39  5-52  6  35  36  38  19-51  7  32  kO  k3  11-54  -  129  -  Needle Length and Fascicle Weight  There is considerable variation in needle length (Table 3 0 ) . There is a s l i g h t increase with height in the crown, and the open grown and edge trees (average 3 . 4 0 cm in length) had longer needles than the interior stand trees (average 2 . 3 5 cm in length). An examination of needle length provides information on,foliage variation, d e f o l i a t i o n effects on needle length coupled with effects on loss in photosynthesis and oviposition s i t e s .  Table 3 0 .  Average needle length (cm) for samples - •• taken from 4 trees in 1 9 7 5 .  Tree  Crown  No.  Lower  Level Mid  Upper  Average  1  2.10  .2.39  2.60  2.36  3  2.23  2.41  2.39  2.34  2.16  2.40  2.49  6  3-31  3.63  3.52  3.49  7  3.01  3.34  3.26  3.34  3.16  3.48  3-39  Average  Average  From a few preliminary samples i t appeared  that the regression  equation of Ives (1955) for calculation of f a s c i c l e weight could be used. The formula i s : Y = 2.988 +  0.04658X  where y = weight of foliage in mg x = total needle length per f a s c i c l e in mm  -  Table 3 1 .  130  -  Average weight of f a s c i c l e as calculated with the use of Ives ( 1 9 5 5 ) formula for an interior ( 1 ) and an edge ( 6 ) tree.  Average Weight of f a s c i c l e (based on hO Tree  Crown  No.  Lower  6  fascicles/level)mg  Level  Mid  Upper  Average  22  32  38  31  51  56  60  56  Intra-branch Variation  in Fascicle Size  Therewas an indication that the f a s c i c l e size i.e. the number or weight of needles per f a s c i c l e increased to the basal  from the d i s t a l  (periphery)  section of the branch, but this trendwas not consistent.  Inter-and Intra-tree Variation  The variation in f a s c i c l e sizes between trees was s i g n i f i c a n t (P >  0.01).  This  indicates that there may  be considerable  variation in  f a s c i c l e size or number between trees, even when the trees appear s i m i l a r . However, this difference is small  between trees  in the same stand positions.  Table 31 shows that the weight of needles per f a s c i c l e varies s i g n i f i c a n t l y with crown level  (lower < mid < upper) and  being lighter in weight on the interior stand tree tree  (56mg).  (31mg)  stand position, than on the edge  - 131 -  Discussion on Needle Fascicles  As was expected the results of the needle f a s c i c l e  analyses  have shown that the top levels, which receive more light and are younger, have more f a s c i c l e s per unit of branch surface than the lower crown levels. Also the upper levels produce more new shoots, and although not the choice oviposition s i t e s , the current shoots would provide good feeding for the f i n a l  sites  instar larvae the following spring.  There is a similar variation in the horizontal d i s t r i b u t i o n of foliage, with f a s c i c l e s per unit branch section increasing from the basal part to the d i s t a l part of the branch.  The differences between the various  sections of side branches was not so pronounced, with the side branches having s i g n i f i c a n t l y more f a s c i c l e s than the main branch. Analyses of the data have therefore indicated that branches should  be sampled from a l l crown levels, because the amount of f o l i a g e  per linear unit of branch d i f f e r s for each l e v e l .  However, to reduce  the amount of work that would be involved, the mid crown level, which is about average, should  be sampled.  A l t e r n a t i v e l y , the side branches  contain about the same number of f a s c i c l e s per unit branch length regardless of crown level and horizontal crown position, and could be used for sampling. The above data and analyses of f a s c i c l e s  provided  quantitative information on the number of eggs in relation to the number of f a s c i c l e s per unit of branch size. of suitable :  This indicated that the a v a i l a b i l i t y  dviposition s i t e s ( i . e . Fascicles)  may actually  have a limiting e f f e c t on the size of insect population.  But both the  searching a b i l i t y of the insect and the s u i t a b i l i t y of available needles w i l l a f f e c t the number of needle f a s c i c l e s u t i l i z e d for o v i p o s i t i o n ,  - 132 -  when f a s c i c l e s are sparse in relation to the number of adults.  The  female moths, as observed in the f i e l d , have s u f f i c i e n t searching to find any f a s c i c l e .  However, a l l of the sites may  not be suitable for  oviposition at the time the insects are laying eggs. may  ability  For example, needles  be heavily damaged (as shown e a r l i e r the insect prefers sound  adventitious needles may shoots may  needles),  not be produced after heavy d e f o l i a t i o n , or  new  not be s u f f i c i e n t l y developed early in the season.  Insect Morta1?ty  Insect Mortality and  Effects on Distribution  As often occurs in sampling, mortality factors can be only by measuring insect population  evaluated  reduction at successive intervals  during various developmental stages.  In this study mortality is assessed  by subdividing the l i f e stages into 4 periods: Period  1: Eggs to third  total mortality of  51  instar or prewinter larvae.  percent  is usually not very high.  for this period  in  197**.  reported  Mortality  due to the unusually  percentage (2k%) of empty eggs, contents of which had (Webb 1953  shows a  Mortality of eggs  No egg parasites were discovered.  of 29 percent of the eggs examined in 1 9 7 4 was  a hemipterous bug.  Table 32  high  been sucked out  by  that k-kO% of the eggs were sucked  out by Deraeocovis nubilis Knight with a mean of 10-15% in eastern Canada). The f i r s t and  second instar larvae l i v e in needle mines, and  cause of mortality is i n t r a s p e c i f i c competition caused by dry weather conditions. eggs are frequently deposited  the chief  in the mines and desiccation  At moderate or high densities, several  per needle, up to 5 eggs/needle in this  -  study.  133 -  If there are several larvae in a needle, those in the t i p portion  which is desiccated e a r l i e r , usually die. The third instar larvae prepare cases, and as free casebearing insects they feed a l i t t l e before dormancy, and as such, are subjected to death by predators. parasite was needle f a l l  Predators are so few as to be negligible, and no  reared or has been reported as k i l l i n g this stage. in autumn may  have some effect  Premature  i f the casebearers are s t i l l  attached to them, or i f the larva is unable to complete i t s case. Period 2:  From third  this period for  instar to fourth instar larvae.  1974-75  was  41 percent  is due to cold or predation by birds.  (Table  32).  Mortality during  Overwintering mortality  Table 33 shows the number and per-  centage of desiccated or empty cases found  in early spring.  for 1^8 percent mortality; the majority of this was  This accounted  larvae whose cases  consisted of needle-tips. Period 3' for  From fourth instar larvae to pupae.  this period was 4 2 percent (Table 3 2 ) .  (including birds and  The mortality of casebearers  This is due mainly to predators  insects) a flock of siskins (Spinus pinus Wilson)  observed on the 19 April  was  1974 at Sheep Creek feeding on casebearers for  about 10 minutes in the mid crown area.  Poor synchronization of the larvae  emerging from dormancy in relation to the budding of the larch has been reported as contributing to mortality.  Parasites play only a very minor  role in mortality at this stage. Period 4:  Pupae to Adults.  the pupal to the adult stage.  Table 32 shows a mortality of 20 percent from This is based on the rearings of pupae collected  on 14 June 1975 just at the time of adult emergence. Therefore, mortality was due to hymenopterous parasites, mainly Spilochalcis sp. and Dicladocerus sp.  -m Table  32.  S u r v i v a 1 o f C. 1 a r i c e l l a through one c o m p l e t e n e a r T h r u m s , B.C • 1 9 7 4- 1 9 7 5 .  S t a g e! O f D e v e l opinent Egg Larva-  .6365 L  l  Larva  2  ( S p r i ng)'  Pupa  1 1  C C  No.  51.1  .1265  40.6  .0788  42.5  .0218  20.4  24. 5  • 1855  .0849 Number o f 1 a r v a e by  33.  • 3250 • 3115  .1067  Adult  T r a p  50  S L ... (Fall)  Larva  Table  S u r v i v a l o f an a v g e g g c o m p l e m e n t o f 50  '0  Morta1i ty  X  p o s t w i n t e r l a r v a e and crown 1 e v e l , 1975Crown  Lower No. D e s i c .  generation  14. 6 8. 4 6. 7 desiccated  Level  Mid No . D e s i c •  Upper No . D e s i c .  Totals L i v e Des i c•  1  0  3  3  77  6  2  1  5  4  45  10  3  4  -  -  38  4  4  8  7  13  62  28  13  15  20  222  48  5  16  4  3  67  23  6  6  12  10  71  28  7  1  20  4  35  25  8  7  3  3  220  13  30  39  20  393  89  9  2  -  1  50  3  10  2  -  1  82  3  11  10  13  9  98  32  12  1  1  -  43  2  15  14  11  273  40  13  2  5  6  34  13  14  1  1  -  36  2  15  8  9  13  49  30  11  15  19  119  ^5  27%  69  83  70  1007  222  18%  Grand T o t a l s  18%  18%  13%  -  Spatial Difference  135  -  in Mortality  Spatial difference in mortality depends mainly on occurrence and  behaviour of b i o t i c and a b i o t i c agents.  particular parts of the crown?.. s p a t i a l l y or females may aggregated.  the  Birds prefer  Parasites can be unevenly distributed  not lay their eggs evenly, but  Weather influences may  frequently  d i f f e r between the various  stand  positions (edge, interior and open trees).  Vertical Distribution of Mortality  Total mortality based on the number of insects per was  greatest  in the upper crown for the egg  to prewinter larval stages  (Per iod 11) , as shown i n Append ix! 4, Tabl es 1 0 , 1 1 and or overwintering  stage, mortality was  than in the lower crown. (Period 3) mortality was  greater  Horizontal  Fig. 1 2 .  For Period  2,  in the mid and upper levels  For the 4 t h instar larval to pupal stages greatest  in the lower and upper crown levels.  Pupal mortality by parasites was crown (Table  fascicle  greatest  in the lower tree  34).  Distribution of Mortality in the Crown  Although variation in the d i s t r i b u t i o n along the branch is due mainly to migration  or the a v a i l a b i l i t y of needle f a s c i c l e s , variation  in mortality could also play an  important part ( T a b l e ^ 3 6 ) .  lower mortality is caused by birds on the twig t i p s .  For example,  This is attributable,  either to higher insect density or possibly because birds do not prefer to s i t on the thin ends of twigs.  Jagsch  (1973)  noticed that bird  -  predation of larvae was  136  -  usually more pronounced on thick branches which  hang down from old trees. Table 36 shows that mortality due to parasites was on the outer section of both the side and main branches.  greatest  This is  probably due to the higher density of larvae on the outer crown section, or the preference of the parasites for this crown section.  This  would account for the non s i g n i f i c a n t difference in parasitism to exposure (Table  between egg and  larva^ to pupa. occurred  Population  i l l u s t r a t e s the seasonal  larch casebearer in the study areas. population  due  35).  Seasonal Fluctuation in Casebearer  Fig. 21  theory  fluctuations in population  Significant declines occurred  larva^, the overwintering  period  of  in  (L^-L^) and  Very l i t t l e decline in numbers from pupa to adult stage  due to low percentage parasitism.  -  Table  34.  137  -  Average number of pupae, adults and parasites per f a s c i c l e by crown l e v e l , 1 9 7 5 -  L e v e l Lower  Mid  Pupae  0.080  0.108  0.091  Adults  0.071  0.100  0.083  Parasites  0.009  0.008  0.008  Table  35-  Upper  Average number of pupae, adults, parasites per f a s c i c l e by exposure and branch type, 1 9 7 5 .  Exposu re  Branch  Exposed  Shaded  Main  Side  Pupae  0.114  0.072  O.O85  0.101  Adults  0.105  0.065  0.079  0.091  Parasites  0.009  0.007  0.006  0.010  Table  36.  Average number of pupae, adults and parasites per f a s c i c l e by horizontal crown position, 1 9 7 5 Main  Branch  Inner  Mid  Pupae  0.069  Adults Parasites  Side  Branch  Outer  Inner  Mid  Outer  0.082  0.105  0.045  0.091  0.165  0.066  0.079  0.090  0.041  0.085  0.148  0.003  0.003  0.015  0.004  0.006  0.017  -  May  June -  Fig.  21.  1  July 9  7  4  138  Nov -  -  Apr  May 1  June 9  7  5  Ju 1 y  —  Casebearer population per f a s c i c l e from May 1 9 7 4 to June 1 9 7 5 .  - 139 -  Recommendations for Sampling  The development of a sampling A l l stages of the larch casebearer  technique is straight-forward.  inhabit the same universe, namely  the tree crown, and population densities of the d i f f e r e n t stages can be estimated by a suitable sampling unit (the needle f a s c i c l e ) taken at appropriate times.  There is one generation per year and no overlapping  of the d i f f e r e n t stages.occur. The Egg Stage:  Eggs are laid singly usually on the underside near the  t i p of the needle.  The evacuated egg skins persist on the foliage for  about 6 weeks or until the third case.  instar larva begins constructing i t s  Therefore, sampling can be delayed until nearly a l l of the eggs  have hatched and thereby provide an estimate of: 1.  the number of s t e r i l e eggs  2.  the number of egg chorions from which the contents were sucked out by predators  3.  the number of f i r s t  instar larvae  Egg samples, however, do present some d i f f i c u l t i e s . Eggs are very small ( 0 . 3 mm),  almost transparent when  hatched, widely, scattered, and r e l a t i v e to the number of needles that must be searched, they;are few in numbers at light population densities. Searching for eggs on foliage by microscopic examination is tedious and slow.  This can be speeded up by rotation of f a s c i c l e s with  the underside of needles exposed under the microscope or magnifier before needles f a l l o f f .  Extreme care in checking is required.  - 140 -  The numbers of eggs are usually high enough to warrant the use of only of few sample trees.  The Larval  Stage  Egg hatch may  be determined  by removing the empty egg and  looking for a mine entrance below i t , survival of the larva in the mine may  be determined  by s l i t t i n g open the mine and teasing out the larvae.  Mortality of this stage is usually low, so that therefore, the d i s tribution in the crown would be similar to that of the egg stage. Prewinter Larvae:  The overwintering larval stage is probably the  easiest to sample because: (a)  the timing is not c r i t i c a l  (b)  i t is easy to count the number of insects (after  (c)  the population is the most stable  (d)  the frequency d i s t r i b u t i o n of the number of larvae per  leaf-fall)  spatially  f a s c i c l e (Table 1) is not as skewed as for the pupal stage There are disadvantages to sampling of this stage: (a)  the degree of d e f o l i a t i o n cannot be estimated, but damage can be estimated at the time of pupal samples  (b)  i f not kept in cold storage, larval a c t i v i t y can commence again on warming up.  The overwintering stage is recommended as the easiest stage to sample.  jnsect  Sampling of the spring larval stage requires c r i t i c a l  timing because of larval a c t i v i t y , the egg stage is very d i f f i c u l t  and time  consuming to count, and sampling of the pupal stage also requires c r i t i c a l t imi ng.  - 141 -  Early Spring larvae: stage.  After the adults, this is the most active  If c o l l e c t i o n is required just before a c t i v i t y commences,  timing can be very c r i t i c a l .  Also, i f larvae are active, some  might be lost during c o l l e c t i o n . Pupa Pupal cases are usually firmly anchored with s i l k strands attached to foliage, at the base of needle f a s c i c l e s , or under lichens, and thus persist for 2 weeks before adult emergence and for 6 weeks, or longer after emergence.  Their aggregating habits makes the straw-brown  cases easy to spot. Late larval populations can be estimated from samples of early pupae. Emergence of adults from pupae may be estimated by samples taken at  the commencement of emergence (on the 14 and 1 5 t h June at Thrums in  1974  and 1975) and provides an estimate of the female and male moth popu-  lation as well as those destroyed by parasites, predators and other causes. Also, adult emergence can be estimated by counting empty pupal cases collected well after adult emergence is completed. Defoliation can be estimated most accurately at this stage. The major disadvantage of this stage is that timing is very c r i t i c a l . The pupal stage is the most important  i f i t is required to  study the parasites affecting the casebearer, as a l l parasites reared to date emerged at the mature larval or pupal stages of the casebearer.  - 142 -  A General  Sampling Design  A practical sampling design for estimating the population density of a l l l i f e stages of the larch casebearer would be a three-stage-'- sampling.  The f i r s t  in a given stand  stage would be the tree,  the second stage would be the crown level within a tree, and the third stage the branches within each crown l e v e l .  The variable to be  estimated should be the number of insects per f a s c i c l e .  In order to  make this design p r a c t i c a l , the number of samples to be taken second and third stage has to be fixed.  in the  Therefore, i t is recommended  that two crown levels should be sampled, the lower and the middle of  the trees, partly because the upper third  third  is very d i f f i c u l t to sample  and partly because the insect population was not s i g n i f i c a n t l y higher in the upper third of the crown than in the middle t h i r d , for any of the stages sampled. For the third stage, two branches should be taken randomly from each of the lower and mid crown levels.  The present study didtnot  indicate the necessity of s t r a t i f y i n g the branches into two groups to  represent shaded and exposed conditions (Appendix 4, Tables 12 S 13) when  s u f f i c i e n t samples are included.  From each branch three 15~cm  lengths  should be cut for observations of the number of insects and number of fascicles.  The pooled sum of the number of f a s c i c l e s per three  samples should constitute one observation.  *  -  This way, one observation  per branch w i l l be the basic observation in the sample. 15-cm  15cm  The three  branch lengths should be randomly selected from the outside  Three-stage sampling is a s t a t i s t i c a l term, and i t should not be confused with the different insect stages. Stage is underlined, when i t is referred to sampling in this thesis.  - 143 -  two-thirds of the branch, since the insect population stem was very low.  close to the  Main and side branches should be given equal  chance to be selected for the 15 cm length. -  Three 1 5 cm sections _  are recommended instead of one 18-inch (45 cm) section f o r easier handling  and for better representation  of the whole branch.  The sum  of these three counts should be used in the analysis of the data to avoid the very large number of zero observations  which would result  in a very skewed frequency d i s t r i b u t i o n . Selection of two branches per crown level and two crown levels per tree w i l l  result in a fixed number of 4 observations  per tree.  The only sample size which has to be calculated in this three-stage sampling design is the number of trees to be sampled.  The sample size  can be calculated from either a p i l o t study or a previous analysis carried out under similar conditions.  The data have to be analyzed  by the following analysis of variance model:  Table 37.  Analysis of variance  for three-stage sampling.  Source of  Components of  Variation Tree  DF n-1  SS  MS  Variance  SS,  MS  n(Z--l)  SS.  M S  Samples within level  nZ(r-l)  SS,  MS  nZr-1  $  2 2 2 +ra +Za L  2  Level within tree  Total  a  T  L  S  a  S a  + r a  s  T  2 L  -  ]hk  -  where n = number of trees in the sample I = number of levels within each tree r = number of samples (branches) within each level 2 0"^  = component of variance for samples within levels and 2 = component of variance for levels within trees 2  o"  = component of variance for trees  T  Sample Size From the information above the required number of trees can be calculated-'- as: MS  T  n  1  =  rl  D  where n D  1  2  = required sample size (number of trees) = desired standard error of the mean in the units of observations  The procedure above was  used to c a l c u l a t e the required number of trees  to be sampled for the three d i f f e r e n t  *  (not in per cent)  stages:  More complicated formula based on the components of variance (Table 3 7 ) is available in texts on sampling techniques, but i t is not warranted here because the number of trees to be sampled in a given stand can be considered very large.  - 145 -  Table 38.  The calculated required number of trees to be sampled by insect stage and sampling precision.  L i f e Stage  Sampli ng  Prec i s ion  of Insect  10%  20%  Pupa  61  16  Egg  14  4  Larva^  40  10  -  ...a-  The sampling precisions were calculated as the per cent of mean obtained from the present study. in untransformed  The analysis in Table 37 has to be calculated  data, because the variances have to be estimated for  the actual observations.  Analysis based on transformed data may under-  estimate the number of trees to be sampled. The three-stage sampling design suggested above w i l l give a r e l i a b l e estimating system for the level of population density of the larch casebearer for a l l the stages covered  in this study.  The data  obtained from the design should be analysed by the analysis of variance model given in Table 37  after using the exponential transformation  ind icated e a r l i e r . The mean  per third stage unit for a stand can be calculated as:  X  =  n 1 Z E E 1 =1 j=l nZ-r  r X k=l  '  J l <  - 146 -  th th X... = an observation from the i tree, j level and k  branch  n = number of trees sampled t = number of levels (2) sampled r = number of branches (2) sampled  The standard error of the mean* is defined as:  MS.J., n,Z and r are from Table 11 for untransformed  data.  From these  s t a t i s t i c s the confidence limits can be computed:  X  +  t Sx  t = student's t with nt (r-1) degrees of freedom for the desired probability l e v e l .  For the present study the mean and the standard error of the mean are given in Table  39 .  A more complicated formula is available for data when the number of trees in a stand is not very large.  - 147 -  39-  Table  Mean (X) and Standard error of the mean (S-) f o r the x various l i f e stages sampled in numbers of insects per f a s c i c l e . Parameter  L i f e Stage of Insect  1974  Pupa  0.1106  0.0170  Egg  0.6365  0.0613  Larva, L„  0.3115  0.0220  Larva, L^  0.1795  0.0122  Pupa  0.0930  0.0084  Egg  0.7492  0.0329  1975  - 148 -  SUMMARY AND CONCLUSIONS  The study was carried out in immature western larch stands infested with the larch casebearer at Thrums near Castlegar and near Salmo in the Nelson Forest D i s t r i c t , of B r i t i s h Columbia,  Canada.  The  sites are typical of the areas of larch casebearer infestations in B r i t i s h Columbia  as reported by the Canadian  Forest Insect and Disease Surveys  since 1966. The stands offered v a r i a b i l i t y in habitat types and permitted the investigation of several factors within one general s i t e .  The investigations  were based on two 1-year generations of the larch casebearer. Sampling  by r e p l i c a t i o n and s t r a t i f i c a t i o n was conducted  in relation to: position of trees in the stand ( i n t e r i o r , edge and opengrown trees); d i f f e r e n t crown levels (lower, middle and upper); d i f f e r e n t branches at the same level based on exposure to sky light  (exposed or  shaded); d i f f e r e n t 15~cm segments (6) of a branch throughout  i t s length;  different stages in the insect's l i f e cycle (egg, larva and pupa). Individual subsamples taken to study insect d i s t r i b u t i o n and to develop a sampling design included: (1)  the pupal stage, May 197**, 540 subsamples from a total of 15  (2)  trees (754*pupae);  the egg stage, July 1 9 7 4 , 3 2 4 subsamples from a total of 9 trees ( 2 , 6 5 0 eggs);  (3)  the i n i t i a l  larval stage, Nov. 1 9 7 4 , 4 3 2 subsamples from  a total of 12 trees ( 1 , 4 0 0 larvae); (4)  the f i n a l  larval  stage, April  1975, 540 subsamples from a  total of 1 5 trees (1,007 larvae,,)  - 149 -  (5)  the pupal stage, June 1 9 7 5 , 540 subsamples from a total of 15 trees ( 6 4 2 pupae); and  (6)  the egg stage, July 1 9 7 5 , 2 8 8 subsamples from a total of 8  trees  (2,624  eggs).  Of the theoretical d i s t r i b u t i o n s tested (normal, binomial, Possion and negative binomial) the negative binomial gave the best f i t to the observed data for a l l l i f e stages except the egg stage which approached the normal d i s t r i b u t i o n . The variance of the number of insects per needle f a s c i c l e , calculated for each tree sampled, was  related to the mean.  Therefore,  approximate normality of the data was achieved by the application of Taylor's power transformation. The results of this study indicated that for a l l insect stages the number of insects per f a s c i c l e was to-tree.  s i g n i f i c a n t l y different from tree-  The averages showed s l i g h t l y more insects per f a s c i c l e on the  edge trees than on the interior or open-grown trees.  This inter-tree  variation indicates that several trees are required in sampling edge or open-grown and suggests that sampling based on interior stand trees alone will  reduce this variation. The 3 crown levels showed s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s in  insect population densities for a l l stages, but the trends were~ different from tree-to-tree.  The differences in crown levels however were, on the  average, highly s i g n i f i c a n t for eggs in 1 9 7 4 and 1 9 7 5 The number of larvae (L^ and L^) and pupae per f a s c i c l e did not, on the average, d i f f e r s i g n i f i c a n t l y between exposed or shaded However, the number of  eggs per f a s c i c l e was  branches.  s i g n i f i c a n t l y higher on  - 150 -  exposed branches than on shaded branches in 1974, whereas the reverse was evident in 1975.  This may be interpreted as owing partly to the lower  intensity of needle d e f o l i a t i o n on exposed branches in 1974, as well as to the greater amount of light along the stand margins or openings. In 1975,  higher infestation on exposed branches reduced the number of  oviposition s i t e s , so that more eggs were deposited on the shaded  branches.  S i g n i f i c a n t l y , more pupae per f a s c i c l e occurred on the side (lateral) branches than on the main branches.  More overwintering larvae  per f a s c i c l e occurred on the main branches than on the side branches  because:  (1) greater number of needles were damaged by larval feeding on the side branches, thereby, leaving less food for the new  larvae to eat; and/or  (2) some i n t r i n s i c behaviour pattern whereby the insect sorts out the better overwintering shelter (under lichens, bark, etc.) offered by the main branch.  This could also account for the fact that the sampling of the  outer 18-inch (45cm) tips of branches by the Canadian Forest Insect and Disease Survey indicated a sharp decline in postwinter population in 1969. The cause of the decline was attributed to the severe winter (-40C in certain areas).  The reason for the subsequent  increase in populations  (1970) was previously given as due to the release of the great potential of the insect to increase when climatic factors became favourable. As a result of this study, i t is proposed that the apparent decline in 1969 and subsequent  increase of casebearer populations was due.to the s h i f t in  densities from the side branches and branch tips to the main branches. The side branches are more subjected to the effects of severe winters than the main branches.  Therefore, heavy mortality of the overwintering  stage in 1969 did occur but mainly on the smaller side branches and tips  - 151  than on the main branch.  -  This therefore indicates a need for a sampling  design that would incorporate representation from both main and side branches in any sampling of the overwintering The egg population was branch positions.  larval  stage.  not s i g n i f i c a n t l y d i f f e r e n t on the  two  Therefore, any portion of the branch can be sampled  for eggs. In general, the population density close to the stem is low for a l l stages, and  increases toward the outer part of the crown.  This is  p a r t i c u l a r l y so for the larvae (and therefore the pupae), as the number of needle f a s c i c l e s (food) per linear unit increases with distance from the stem to periphery and on side branches.  This finding indicates the need  for sampling from the entire branch or making adjustment for the v a r i a t i o n in insect d i s t r i b u t i o n .  However, in heavy infestations the d i s t r i b u t i o n  of eggs w i l l follow that of the undamaged needles ( i f no r e f o l i a t i o n occurs). The female adults deposit eggs singly and scattered over the tree crown with the result that, assuming that s u f f i c i e n t numbers of eggs are available, most needle f a s c i c l e s receive some eggs.  This represents a degree  of randomness, which is important i f mortality through competition needle-mines is to be avoided. d i s t r i b u t i o n of eggs are:  in the  Other habits of the adults responsible for  their tendency to concentrate  oviposition in the  most illuminated zones of the habitat, with the result that egg density is d i r e c t l y related to both position of trees in the stand had more eggs) and height  in the tree.  by i r r e g u l a r i t y or heterogeneity  (open grown trees  Spatial d i s t r i b u t i o n is dominated  of habitat, as the female adult seeks out  undamaged needles to deposit her eggs.  - 152 -  Eggs are laid over the entire branch, and not only on the current shoot growth as reported by Sloan (1965) in Michigan, U.S.A. Egg-deposition s i t e preferences f o r egg laying as found study  were:  infestation.  in the present  (1) Adventitious needles, by r e f o l i a t i o n after heavy However, after 3 years of continuous r e f o l i a t i o n the stand  of trees would stop producing adventitious needles; (2) Undamaged old growth foliage;  (3) Current shoot, which probably do  not develop in  time for egg laying, and the short spike-like needle shapes are not conducive to oviposition.  Sloan also mentioned that adult females preferred current  shoots of about 5"10 cm. in length. The mid-section of the branch had the greatest density of pupae. This indicates that most of the feeding by larvae commenced on the outer section in early spring. the natural  The pupal stage is the stage from which most of  insect parasites emerges.  are, Dicladocerus westwoodii  The most common indigenous parasites  (Eulophidae) and Spilochalcis albifrons  ( Cha1cididae). Dicladocerus adults appeared  to lay eggs on nearby casebearer  larvae on the same branch and on a l l portions of the tree crown.  Spilochalc i s  parasitizes casebearer larvae mainly in the lower crown level and on the two outer portions of the crown.  This indicates the need for sampling  mature larvae or pupae for parasites by taking samples from many d i f f e r e n t branches  in the d i f f e r e n t v e r t i c a l and horizontal positions in the tree  crown. F i n a l l y , a sampling method which considers s h i f t s in populations in the tree crown has been developed for the larch casebearer on western  larch.  -  153  -  LITERATURE CITED  Andrews, R.J., E.V. Morris and N. Bauman. 1 9 6 7 - Larch casebearer, Coleophora lar i c e l l a (Hbn.) p p . 1 3 5 1 3 7 - J_n, Annual D i s t r i c t Reports Forest Insect and Disease Survey B r i t i s h Columbia 1966. For.Res.Lab. V i c t o r i a , B.C. Inf.Rep. 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Estimation of egg populations of the larch sawfly, Pristiphora erichsoni i (Htg.); Can.J. Zool. 33_: 370-388. Ives, W.G.H. 1959- A technique for estimating tamarack foliage production. A basic detailed population study of the larch sawfly. Can. Entomol. 91=513-519. Jagsch, A. 1973- Population dynamics and parasite complex of the larch casebearer moth European larch. App. Entomol. 73_: 1-42. Jung, W.  1942. Contributions to the knowledge of the larch casebearer (Coleophora l a r i c e l l a Hbn.). Z. ang. Entomol. 29_:475_517. (Trans 1 at ionJT  K a t t i , S.K. and J. Gurland. 1962. Efficiency of certain methods of estimation for the negative binomial, and the Neyman type-A d i s t r i b u t i o n s . Biometrika 35:6-15. Kozak, A. and D.D. Munro. I963. An I.B.M. 1620 computer program to f i t frequency d i s t r i b u t i o n s . Forestry Chron. 39= 337 338. -  Kozak, A. and J.H.G. Smith. 1965- A comprehensive and f l e x i b l e multiple regression program for electronic computing. Forestry Chron.  4j_: 438-443.  Krajina, V.J. 1965- Ecology of forest trees in B r i t i s h Columbia. Ecol. of Western N.A. 2: 1-146. Legay, J.M. 1963 - A propos de la repartition de la cecidomyie du Hetre, Mi kiola fag i . Un exemple de d i s t r i b u t i o n binomiale negative. Ann. Epiphyt. Cl4:49~56.  -  156  -  LeRoux, E.J. and C.Reamer. 1959Variation between samples of immature stages, and of mortalities from some factors, of the eyespotted bud moth, Spilonota ocellana (D. & S.) (Lepidoptera: 01ethreutidae), and the pistol casebearer, Coleophora s e r r a t e l l a (L.) (Lepidoptera:Coleophoridae), on apple in Quebec. Can.Entomol. 9]_: 428-449. Loos, C.  1891-92. Einige Beobachtungen uber Coleophora l a r i c e l l a auf dem Schluckenauer Domanengebiete. Centralbl. f.d. Forstwesen. 17:375~379; 18:425"531 (from Webb, 1953).  McGuire, J.U., T.A. Brindley and T.A. Bancroft. 1957The d i s t r i b u t i o n of European corn borer larvae, Pyrausta nubi1 a 1i s (Hbn.) in f i e l d corn. Biometrics 1 3'• 65~78. Morris, R.F. 1955The development of sampling techniques for forest insect d e f o l i a t o r s , with particular reference to the spruce budworm. Can.J.Zool. 33:225-294. Moriuti, S. 1972. Two new economically important species of Microlepidoptera infesting larch in Japan (Lepidoptera: Coleophoridae and T o r t r i c i d a e ) . Kontyu 40:254-262. Neyman, J.  1939On a new class of 'contagious' d i s t r i b u t i o n s , applicable in entomology and bacteriology. Ann.Math. Stat. J_0: 35-57-  Oakland, G.B.  1953-  Determining  sample size.  Can.Entomol. 85:108-113. Bull.No. 5 Maine  Peirson, H.B. 1927Manual of forest insects. Forest Service. 13PPPiatt, R.B.  and J.F. G r i f f i t h s . 1964. Environmental Measurement and interpretation. Reinhold Pub. Corp. N.Y. 22.  Quednau, F.W. 1967. Notes on mating, oviposition, adult longevity, and incubation period of eggs of the larch casebearer, Coleophora l a r i c e l l a (Lepidoptera:Coleophoridae), in the laboratory. Can.Entomol. 99j397~401. Quenouille, M.H. 1950. Introductory S t a t i s t i c s . London. 248pp. Ratzeburg, J.T.C. I869. Die Wa1dverderber und 160-162. Berlin, (from Webb, 1953). Reissig.  1869(Tin.  Pergamon Press,  ihre Feinde  6^72,  Die Larchenmotte, Coleophora l a r i c e l l a Hb., 1ar ic i nel1 a Bchst.) Z e i t . f . Forest-und Jagdwesen. 1:129-137. (from Webb, 1953).  - 157 -  Roe, A.L., R.C. Shearer and W.C. Schmidt. 1970. Management of western larch. (Manuscript in preparation). From, Management of western 1 arch.... Northern Region. U.S.D.A. For.Service Handbook FSH2471.15RI. Rojas, B.A. 1964. La binomial negativa y la estimacion de intensidad de plagas en el suelo. Fitotecnia Latinamer. J_:27~36. 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Biotic factors affecting populations of the larch casebearer, Coleophora l a r i c e l l a Hbn., in Wisconsin. Ph.D. Thesis, Univ. of Wis., Madison, Wisconsin. 193PPSouthwood, T.R.E. 391pp.  1966.  Ecological Methods.  Methuen Co., London.  Taylor, L.R. 1961. Aggregation, variance and the mean. 189:732-735.  Nature Lond.  Taylor, L.R. 1965A natural law for the spatial disposition of insects. Proc. XII. Int. Congr. Entomol. pp.396-397. Tunnock, S., R.E. Denton, C.E. Carlson and W.W. Jansen. 1969Larch casebearer and other factors involved with deterioration of western larch stands in northern Idaho. USDA Forest Serv. Res. Pap. lnt-68. 10pp.  - 158 -  Waters, W.E. and W.R. Henson. 1959- Some sampling attributes of the negative binomial d i s t r i b u t i o n with special reference to forest insects. Forest S c i . 5_:397"4l2. Webb, F.E. 1953. An ecological study of the larch casebearer Coleophora l a r i c e l la Hbn. (Lep idoptera : Col eophor idae) . (Unpublished") Ph.D. Thesis, Univ. of Michigan. 212pp. Webb, F.E. 1957- Sampling techniques for the overwintering stage of the larch casebearer. Can. Dep. Agr. Bi-Monthly Prog. Rep. 1 3 00:1-2. Webb, F.E. and F.W. Quednau. 1971. Coleophora l a r i c e l l a (Hubner), larch casebearer (Lepidoptera:Coleophoridae). In Biological control programmes against insects and weeds in Canada 1959-1968. Tech. Comm. No.4, Comm. Inst. B i o l . Contr. 266pp. Williams, C.B. 1964. Patterns in the balance of nature. In, Theoretical and experimental biology Vol. 3, Academic Press, New York. 325pp. Van Poeteren, N. 1933- Verslag over de werksaamheden van den Plantenziekten kundigen Kienst in het jaar 1932. Versl . PI. Ziektenk. Dienst. 72. Wageningen.  -  Appendix 1.  159  -  Pupal data sheet and sampling  notes.  -  LARCH  Tree No.  Crown I  Branch  CASEBEARER  Length  PUPAL DATA SHEET  Date C o l l e c t e d :  Branch  No.  of  Exposure Level  159a -  Sect ion  1  2 3  It  5 6 1 2 3 *» 5 6 1 2 3  k 5 6 1 2 3 1> 5 6 1 2 3 5 6 1 2 3 5 6  Fascicles  Area:  %  Damage Q Vol  No.of Pupae,  Crown Class:  No.Emerged Casebearer Tot  J  Emergence Remark: Date  - 160 -  LARCH CASEBEARER —  TREE  SAMPLING NOTES  Nos. 1 -  k  Interior stand trees  5 -  8  Edge trees  9-12 13  CROWN LEVEL  -  15  near Thrums, B.C.  Open grown trees near Sal mo,  Open clusters  B.C.  U = Upper M = Middle L = Lower  EXPOSURE  S = sampled branch shaded e.g. by other tree(s) L = sampled branch not shaded e.g. facing out from stand  BRANCH SECTION (15-cm or 6-inch length) Nos. 1, 2, 3 for main branch.starting from the stem k,  5, 6 for side branch starting from the stem  DEFOLIATION RATING (see Text) 0 = Negligible -- no v i s i b l e d e f o l i a t i o n 2 = Light -- up to 2 5 % d e f o l i a t i o n k = Moderate —  26 to 5 0 % d e f o l i a t i o n  6 = Heavy -- 51 to 7 5 % d e f o l i a t i o n 10 = Severe -- over 7 5 % d e f o l i a t i o n  -  Appendix 2.  161  -  Form used for egg counts.  - 161a -  EGG COUNTS —  JbATL  «J  Ul  COLLECT£bi  P lis  VI  BL 1  AfiEA ••  11  M UJ  1  S  LARCH CASEBEARER  CL. VOL.  s 1  >u  5 EGG  a: S v: i % s:  e  vl  NO. Of L&C/FAS. . I l l  I i  4  r  (,  BS 1  I I  $ £  ML I  1 3  f  S (,  us/ z 3  f c  out I 3  * C I 3 S  (,  •  + 5"  PQRWN DF NECbLB  AP.  Mm. BASE  NEEDLE NtRbLE  1 *  SURFACE  vi. ^j  a,  - 162 -  Appendix 3«  Form used for larval counts.  - 162a -  LARCH CASEBEARER — JiATB  AREAi  COLLECTED ••  TAtE  NO.  CAOIV/V T/\tB  «a 5:  LARVAE DATA CLASS:  NO.  VJ  Q  Vj  "  5  VO  5  VJ ;  HI •  Hi  Appendix k.  Tabl  Table 1.  Observed and expected frequencies for pupae per f a s c i c l e per 15-cm branch section. Frequency Di str i but ions  CI ass  -  Middle  Obs.  0.025  255  0.075  0.175  79 58 30  0.225  33  0.275 0.325 0.375 0.425  0.125  0.475 0.525 0.575 0.625  1974 -  Neg. Binom.  Obs.  Neg.Binom.  Chi-sq.  260.8  0.13  316  323.4  94.8  2.64  74  72.0  0.17 0.05  56.0  0.07 1.30  47 25  39.1 25.4  1.59 0.01  1.80  17  17.9  0.04  23  36.9 26.1 18.8  0.91  14  13.1  14  13.8  0.00  10  9 11 8  10.3 7.9 6.0^) 4.8 y 3.6  0.17 1.22  3 9 4  9.9 7.7 6.0  0.05 0.00  13 7  12.94  0.675 0.725 0.775 0.825  5 4 2 2 0 3 0 0  0.875 0.925 0.975  0  c  c  0  J  1.475 Total: Significant  - 1975 "  Chi-sq.  540  (P = 0.01)  540  ) 2 21.21 * df 7  540  4.7 3.8 3.1 2.5 2.0 1.6^ 1.4  2.85 1.47 0.12 0.37 0.27 0.10 0.00  1.1 0.9 0.8 r*  vl  0.15  7.25 12  df  Table  2.  O b s e r v e d and e x p e c t e d  frequencies  Class  Frequency -  Middle  f o r pupae p e r 1 5 c m  Obs.  1974  -  1975  -  Chi-sq.  section.  Distributions  -  Neg. Binom.  branch  Obs.  Neg.  ~  Binom.  Chi-sq.  0  250  252  0.01  301  302  0.00  1  116  119  0.08  111  105  0.38  2  62  67  0.41  49  54  0.44  3  42  40  0.09  23  31  1.94  4  29  25  0.82  27  18  3.95  5  13  15  0.31  8  11  0.98  6  14  10  2.08  5  7  0.62  7  4  6  0.65  2  5  1.39  8  5  4  0.37  3  3>  9  5  2  2.70  5  2  5  1  10  Total :  540  7.54 7  df  2.89  12.59 6  df  Table 3 -  frequencies for eggs per f a s c i c l e per 15 cm branch section.  Observed and expected  -  Class  Frequency 1Di str ibut ions  Middle  Obs.  0.05  1974  -  -  Normal  Neg.Binom.  23  11.2  12.0  0.15  27  15.7  24.7  0.25  26  20.6  0.35  30  0.45  Chi-sq  Obs.  Normal  1975  Chi-sq.  Neg.B inom.  Chi-sq.  24  8.6  0.20  12  11.6  1.6  33.7  1.77  26  15.0  8.0  24.1  0.14  25.4  38.1  1.72  22  18.4  0.6  28.3  1.42  23  29.4  38.1  5.97  20  21.5  0.1  29.7  3.17  0.55  47  31.9  36.3  3.14  25  23-9  0.0  28.9  0.53  0.65  27  32.5  31.5  0.65  18  25.3  2.1  26.6  2.82  0.75  25  31.0  26.7  0.11  20  25.4  1.1  23.6  0.56  0.85  20  27.8  21.9  0.17  20  24.4  0.7  20.3  0.00  0.95  12  23.5  17.3  1.66  10  22.2  6.7  17.0  2.92  1.05  20  18.5  13.9  2.62  21  19.3  0.1  14.0  3.46  1.15  7  13.8  10.4  1.13  13  15.9  0.5  11.3  0.24  1.25  8  9.6  8.0  0.00  6  12.5  3.4  9.0  1.02  1.35  4  6.3  5.9  0.62  10  9.4  0.00  7.1  1.16  1.45  25  3.8  5.1  37  6.7  Total:  324  High values excluded from t o t a l .  19.77  288  7.8  16.9  0.05  5.5  25.6  17.53  Table 4.  Observed and expected frequencies for larvae per f a s c i c l e per 15 cm branch section -  Frequency Distributions  r l  L  1974-75.  I3  S S  Prewinter Larvae  Postwinter Larvae  Middle  Observed  Ne§. Binom.  0.025  103  104.7  0.02  0.075 0.125  42  4.85  31  58.9 43.4 34.0 27.8  0.275 0.325 0.375 0.425  34  23.2  24  19.5  13  16.4  14  14.1  0.475 0.525  13 9 8  12.1  0.175 0.225  49 31  Chi-sq.  0.73 0.26  7  0.13 0.10  0.675 0.725  5 4  6.9 6.0  0.51 0.66  0.775 0.825  6  5.3 4.6\  0.10  0.875 1.475 Total:  ' 432  V 32.3  1.0J  Chi-sq.  0.03 O.65 3.00 1.05 0.03  19  29.9 23.3 19.5  0.07 0.01  14  14.9  0.05  8 6 16 6  12.1 9.9 8.3 6.8  1.39 1.55 7.05 0.10  7  5-7  0.29  2>v  4.7^ 3-9  3 2  i  1 30 2f  4.0/ 39  85.5 55.1 39.4  33  1.05 0.71 0.00  9.1 7.9  'A  78 68 29 22  10.5  Neg. Binom.  206.7  204  0.37 5.00  0.05 0.20  0.575 0.625  Observed  3.3 2  2  -  8  -  k  1.39 •  16.13  % 540  1.3J 16.91  Table  5.  Observed and e x p e c t e d  f r e q u e n c y f o r l a r v a e p e r 15-cm  Frequency  Class Prewinter Middle  Obs.  Neg.  section  Postwinter Chi-sq.  1974-75.  Distributions  Larvae  Binom.  branch  Obs.  Neg.  Larvae  Binom.  Ch i - s q .  0  101  101 .4  0.00  199  199.1  0.00  1  90  80.6  1 .08  141  119.5  3.88  2  54  62.0  1 .03  74  76.0  0.05  3  54  47.2  0.97  39  49.3  2.15  4  37  35.7  0.04  23  32.3  2.67  5  22  26.9  0.90  21  21.3  0.00  6  24  20.3  0.68  10  14.0  1.16  7  10  15.2  1.78  8  9.3  0.18  8  8  11.4  1 .02  5  6.2  0.22  9  1  8.5  6.65  5  4.1  0.19  10  5  6.4  0.31  1  2.7  1.10  11  5  4.8  0.01  3  1.8  0.76  12  5  3.6  0.55  1  1.2  0.03  13  2  2.7  0.17  3  0.8  5.88  14  4  2.0  1.95  2  0.5  3.91  15  1  1.5  0.16  1  0.4  1.12  16  1  1.1  0.01  3  0.2  -k /V  17  1  0.8  0.03  0  0.2  0.16  18  8  0.6  Total: ** H i g h v a l u e e x c l u d e d f r o m  17.35 total.  23.50  168 -  -  Table 6.  Analyses of variance of eggs per f a s c i c l e by tree, crown l e v e l , exposure, branch type and horizontal crown position. Egg - 1974 DF  Source  MS  F  Egg DF  1975  MS  F  6.8**  Tree  T  8  0.332  5.0**  7  1.229  Level  L  2  0.899  13.5**  2  2.560 14.2**  Exposure  E  1  0.167  2.5  1  0.513  2.8  Main & side branch  M  1  0.004  0.1  1  2.664  14.8**  Parts, within M  P  4  0.437  6.6**  4  0.298  1.6  0.081  1.2  0.428  2.4*  T x L  16  14  T x E  8  0.073  1.1  7  0.125  0.7  T x M  8  0.070  1.1  7  0.149  0.8  T x P  32  0.063  0.9  28  0.335  1.9*  L x E  2  0.013  0.2  2  0.010  0.1  L xM  2  0.149  2.2  2  0.480  2.7  L x P  8  0.052  0.8  8  0.350  1.9  E x M  1  0.052  0.8  1  0.434  2.4  E x P  4  0.057  0.9  4  0.030  0.2  T x L x E  16  0.073  1.1  14  0.675  3.7**  T x L x M  16  0.091  1.4  14  0.263  1.5  T x L x P  64  0.062  0.9  56  0.180  1.0  T x E x M  8  0.119  1.8  7  0.086  0.5  T x E x P  32  0.040  0.6  28  0.211  1 .2  L x E x M  2  0.071  1.1  2  0.087  0.5  L x E x P  8  0.016  0.2  8  0.171  0.9  1.6  14  0.134  0.7  56  0.180  TLEM  16  0.109  ERROR  64  0.066  TOTAL  323  * S i g n i f i c a n t within the 0.05  287 l e v e l . ** S i g n i f i c a n t within the 0.01  level.  -  Table 7.  169  -  Analyses of variance of prewinter and postwinter larvae by tree, crown 1evel, exposure, branch type and horizontal crown pos i t ion. Larvae^  Source  Larvae^  DF  MS  F  DF  MS  F  TREE  T  11  0.158  4. 5**  14  0.561  4.2**  LEVEL  L  2  0.502  14.4**  2  0.825  6.2**  EXPOSURE  E  1  0.047  1.4  1  0.472  3-5  MAIN & SIDE BRANCH  M  1  0.460  13.2**  1  1.193  8.9**  PARTS, within M  P  4  0.053  1.5  4  1.230  9. 2**  T x L  22  0.032  0.9  28  0.305  2.3**  T x E  11  0.061  1.7  14  0.200  1.5  T xM  11  0.062  1.8  14  0.152  1.1  T xP  44  0.028  0.8  56  0.180  1.3  L x E  2  0.045  1.3  2  0.670  5.0**  L xM  2  0.023  0.7  2  0.087  0.6  L x P  8  0.050  1.4  8  0.136  1.0  E xM  1  0.002  0.1  1  0.062  0.5  E xP  4  0.021  0.6  4  0.235  1.7  T x L x E  22  0.043  1.2  28  0.140  1.0  T x L xM  22  0.024  0.7  28  0.169  1.3  T x L x P  88  0.040  1.2  112  0.186  1. 4*  T x E xM  11  0.031  0.9  14  0.081  0.6  T x E xP  44  0.035  1.0  56  0.109  0.8  L-x E x M  2  0.030  0.8  2  0.012  0.1  L x E x P  8  0.022  0.6  8  0.211  1.6  TLEM  22  0.039  1.1  28  0.145  1.1  ERROR  88  0.035  112  0.134  TOTAL  431 Significant within the 0.05 level Significant within the 0.01 level  539  -  Table 8 .  170 -  Analyses of variance of pupae per f a s c i c l e by tree, crown l e v e l , exposure, branch type and horizontal crown position. Pupae  Source  '75  Pupae  '74  DF  MS  F  MS  14  0.126  4.5**  0.518  7.9**  F  Tree  T  Level  L  2  0.057  2.0  0.183  2.8-  Exposure  E  1  0.330  11.7**  0.163  2.5  Main S side branch  M  1  0.155  5.5*  2.282  34.9**  Parts, wi thin M  P  4  0.351  12.5**  0.445  6.8**  T x L  28  0.053  1.9*  O.O83  1.3  T x E  14  0.038  1.3  0.019  0.3  T xM  14  0.079  2.8**  0.137  2.1*  T x P  56  0.054  1.9**  0.074  1.1  L x E  2  0.024  0.8  0.010  0.1  L xM  2  0.234  8.3**  0.000  0.0  L x P  8  0.033  1.2  0.026  0.4  E xM  1  0.001  0.0  0.242  3.7  E x P  4  0.020  0.7  0.026  0.4  T x L x E  28  0.062  2.2**  0.086  1.3  T x L x M  28  0.034  1.2  0.061  0.9  T x L x P  112  0.031  1.1  0.057  0.9  T x E xM  14  0.022  0.8  0.032  0.5  T x E x P.  56  0.039  1.4  0.057  0.9  L x E xM  2  0.000  0.0  0.067  1.0  L x E x P  8  0.043  1.5  0.052  0.8  28  0.044  1.6  0.052  0.8  TLEM ERROR  111  TOTAL  538  Significant within the 0.01  0.028  0.065  l e v e l * Significant within the 0.05  level.  -  Table 9 .  171  -  Average number of insects per f a s c i c l e by tree and position in the stand. N  1  Tree  1 9  No.  Pupa  1  0.041  2  0.107  3 4  S 7  E  C  T  S  T  4  A G E 1  9  7  Larva^  Larva,  0.414  0.312  0.102  -  0.424  0.338  0.106  0.075  0.814  0.143  0.470  0.203  0.124  0.153**  0.470  0.155  0.576  0.233  0.180  0.142  0.615  0.112  0.485  0.297  0.180  0.118  0.633  5  0.345  0.566  0.275  0.282  0.158  0.783  6  0.173  0.603  0.358  0.199  0.075  0.692  7  0.148  0.748  0.211  0.189  0.109  0.867  8  0.060  -  0.754  0.513  0.108  -  Edge+  0.181  0.639  0.399  0.296  0.112  0.779  9  0.085  0.607  0.399  0.156  0.128  1.103  10  0.099  0.922  0.251  0.187  0.134  -  1 1  0.078  0.812  0.147  0.151  0.095  -  12  0.078  -  0.155  0.072  0.018  0.649  0pen+  0.085  0.783  0.238  0.142  0.093  O.876  13  0.034  -  -  0.063  0.038  -  14  0.037  -  -  0.082  0.029  -  15  0.071  -  -  0.073  0.029  -  C1 uster+  0.047  -  -  0.073  0.032  -  Stand Avg.  0.122  0.636  0.311  0.185  0.107  0.713  1nter ior+  Egg  4  No samples taken. New trees selected in 1 9 7 5 +  Average f o r position of trees in the stand.  Pupa  5  Egg**  -  172 -  Table 1 0 . Average No.of insects per f a s c i c l e by tree and crown position, 1 9 7 4 . p T  r  e  e  upa  Egg  Crown Position  Larva,  Crown Position  Crown Position  No Lower  Mid  Upper  Lower  Mid  Lower  Mid  Upper  -  -  0.267  0.668  0.308  1  0.023  0.036  0.066  2  0.129  0.081  0.111  0.170  0.552  0.551  0.293  0.323  0.398  3  0.129  0.155  0.145  0.534  0.459  0.417  0.212  0.163  0.235  4  0.118  0.135  0.214  0.409  0.523  0.795  0.288  0.196  0.217  0.100  0.102  0.134  0.371  0.511  O.588  0.265  0.337  5  0.282  0.486  0.268  0.541  0.523  0.635  0.043**0.209**  0.572  6  0.220  0.189  O.lio'  0.570  0.592  0.645  0.305  0.561  0.207  7  0.125  0.184  0.137  0.570  0.800  0.873  O.I85  0.265  0.183  8  0.121  0.044  0.018  -  0.902  1.023  0.337  0.187  0.226  0.132  O.56O  O.638  0.718  0.359  0.514  0.325  9  0.076  0.117  0.063  0.436  0.753  0.633  0.365  0.501  0.332  10  0.056  0.181  0.061  0.620  0.855  1.290  0.139  0.218  0.395  11  0.064  0.115  0.057  0.696  0.901  0.842  0.112  0.170  0.160  12  0.094  0.072  0.070  -  0.118  0.119  0.229  0pen+  0.072  0.121  0.063  0.584  O.836  0.922  O.I83  0.252  0.279  13  0.027  0.060  0.016  -  -  -  -  14  0.058  0.025  0.028  15  0.065  0.101  0.074  -  -  -  -  Cluster+  0.050  0.062  0.039  0.132  0.094  lnterior+  Edge+  Stand Avg. 0 . 1 0 6  -*  Upper  0.505  0.662  *  No samples taken.  **  Shaded branches attacked by bark beetles.  +  Average for position of trees in the stand.  -  0.742  0.269  O.368  0.289  O.298  -  Table 1 1 .  173 -  Average No. of insects per f a s c i c l e by tree position in stand and crown position, 1 9 7 5 -  Tree Crown Position  Crown Position  Crown Position  No Lower  Mid  Upper  Lower  Mid  1  0.279  0.278  0.378  0.061  0.184  0.0604  -  2  0.103  0.129  0.088  0.068  0.063  0.0927  3  0.064  0.123  0.184  0.139  0.212  4  0.297  0.101  0.143  0.198  0.158  O.I98  lnterior+ 0 . 1 8 6  Lower  Mid  Upper  0.520  0.758  1.163  0.108*  0.444  0.432  0.535  0.195  0.031  0.476  0.519  0.849  0.116  O.I63  0.073  0.480  0.570  0.849  5  0.279  0.384  0.184  0.279  0.104  0.091  O.58I  0.663  1.104  6  0.266  0.177  0.153  0.061  0.107  0.057  0.368  1.012  O.696  7  0.308  0.121  0.139  0.094  0.075  0.159  0.955  0.800  0.846  8  0.653  0.571  0.316  0.053  0.107  0.164  -  0.376  0.313  0.198  0.122  0.098  0.118  0.635  0.825  0.882  0.206  0.108  0.161  0.079  0.251  0.053  0.927  1.251  1.132  10  0.162  0.144  0.255  0.048  0.130  0.222  0.239  0.901  0.808  11  0.018  0.113  0.322  0.052  0.090  0.144  12  0.027  0.063  0.127  0.031  0.007  0.015  "  0.103  0.107  0.216  0.052  0.119  0.108  O.583  1.076  0.970  13  0.050  0.098  0.042  0.000  0.061  0.052  -  14  0.059  0.085  0.101  0.017  0.013  0.058  -  15  0.135  0.073  0.012  0.013  0.017  0.056  -  -  0.081  0.086  0.052  0.010  0.030  0.055  -  -  -  0.171  0.174  0.080  0.108  0.091  0.564  0.792  O.89I  Edge+ 9  0pen+  "  Cluster+  Stand A v g . 0 . 1 9 4  * +  Upper  New larch trees selected in 1 9 7 5 Average for positions in the stand  - 174 -  Table 12.  Average No. of insects per f a s c i c l e by tree position in stand and exposure, 1974.  Tree  Pupa Exposed  Shaded  1.  0.026  0.056  — /V  2  0.097  0.117  0.387  3  0.139  0. 148  4  0.161  1 nter ior+ 0.119  No.  Larva  Egg Exposed  Shaded  Exposed  Shaded  0.242  0.586  0.462  0.207  0.469  0.574  0.366  0.312  0.094  0.150  0.701  0.451  0.299  0.168  0.157  0.554  0.426  0.265  0.329  -  5  0.337  0.353  0.546  0.587  0.284  0.265  6  0.141  0.205  0.587  0.618  O.38O  0.336  7  0.128  0.169  0.795  0.700  0.133  0.289  8  0.040  0.081  1 .074  0.434  0.161  0.202  0.643  0.635  0.468  0.331  0.087  0.084  0.653  0.563  0.484  0.315  10  0.080  0.118  1.000  0.844  0.271  0.231  11  0.077  0.080  0.903  0.727  0.158  0.136  12  0.073  0.084  0.184  0.126  0.079  0.091  0.274  0.202  13  0.030  0.038  -  -  -  -  14  0.018  0.057  -  -  -  -  15  0.080  0.062  -  -  -  -  0.043  0.052  -  -  -  -  Stand Avg,.0.101  0.120  0.336  0.287  Edge+  9  0pen+  CI uster+  * +  -  0.852  0.683  No samples taken Average for position of trees in stand  -  0.711  0.590  - 175 -  Table 13- Average No.of insects per f a s c i c l e by tree and exposure,  Larva  Tree No.  Pupa  Egg*  Exposed  Shaded  Exposed  Shaded  Exposed  Shaded  1  0.260  0.364  0.117  0.087  0.744  0.884  2  0.081  0.132  0.102  0.047  0.410  0.531  3  0.099  0.149  0.165*  0.142  4  0.155  0.205  0.163  0.127  0.598  0.631  0.212  0.137  0.101  0.584  0.682  I nter ior+ 0.149  — /V ~i\  -  5  0.453  0.112  0.235  0.081  0.882  0.684  6  0.227  0.171  0.090  0.059  0.603  0.780  7  0.236  0.142  0.154  0.065  -  -  8  0.472  0.555  0.144  0.072  0.789  0.945  Edge+  0.347  0.245  0.156  0.069  0.755  0.803  9  0.193  0.123  0.182  0.073  1.048  1.160  10  0.265  0.109  0.196  0.071  -  -  11  0.105  0.198  0.054  0.137  -  -  12  0.068  0.077  0.009  0.026  0.575  0.723  0pen+  0.158  0.127  0.110  0.076  0.811  0.941  13  0.077  0.049  0.038  0.038  -  -  14  0.086  0.077  0.037  0.022  -  -  15  0.069  0.077  0.026  0.031  -  -  Clusters-  0.077  0.068  0.034  0.030  -  -  Stand Avg.  0.190  0.169  0.114  0.072  0.706  0.792  A  New  j- j -  No samples taken.  +  Average for position of trees i n the stand.  trees selected in  1975-  1975-  - 176 -  Table 14. Average No.of insects per f a s c i c l e by tree and branch type, Pupa  1974.  La rva  Egg-  Tree  Ma i n  S i de  Main  S ide  Ma i n  Side  No.  Branch  Branch  Branch  Branch  Branch  Branch  1  0.045  0.038  -  -  0.537  0.291  2  0.049  0.166  0.367  0.481  0.418  0.258  3  0.146  0.140  0.330  0.609  0.232  0.174  4  0.193  0.117  0.638  0.514  0.233  0.234  0.108  0.115  0.445  0.535  0.355  0.239  5  0.260  0.431  0.634  0.499  0.406  0.143  6  0.145  0.201  0.607  0.598  0.461  0.254  7  0.092  0.205  0.725  0.770  0.253  0.168  0.063  0.058  -  -  1.005  0.503  Edge+  0.140  0.224  0.655  0.622  0.531  0.267  9  0.063  0.108  0.662  0.554  0.623  0.176  10  0.058  0.140  0.949  0.894  0.240  0.261  11  0.037  0.120  1.021  0.604  0.143  0.151  12  0.033  0.124  -  -  0.160  0.150  0pen+  0.047  0.123  0.877  0.684  0.291  0.184  13  0.026  0.043  -  -  -  -  14  0.007  0.068  -  -  -  -  15  0.026  0.116  -  -  -  -  Cluster+  0.020  0.076  -  -  -  -  Stand Avg  0.083  0.138  0.659  0.614  0.393  0.230  1nter ior+  8  +  \  Average for position of trees in the stand.  - 177 -  Table 15- Average No.of insects per fasc i c l e by tree and branch type - 1975.  Tree  Larva  - 1975  Pupa  - 1975  Egg -  1975*  No.  Ma i n Branch  S i de Branch  Ma i n Branch  S ide Branch  Ma i n Branch  S i de Branch  1  0.367  0.257  0.092  0.112  0.970  0.658  2  0.093  0.120  0.053  0.097  0.538  0.403  3  0.097  0.149  0.230  0.077*  0.707  0.522  4  0.159  0.202  0.171  0.118  -  -  1nter ior+  0.179  0.182  0.136  0.101  0.738  0.527  5  0.318  0.246  0.208  0.108  0.784  0.781  "6  0.244  0.154  0.023  0.126  0.768  0.615  7  0.248  0.130  0.065  0.154  0.997  0.737  8  0.445  0.582  0.052  0.164  -  -  Edge+  0.314  0.278  0.087  0.138  0.850  0.711  9  0.191  0.125  0.171  0.085  1.165  1 .042  10  0.134  0.240  0.062  0.205  0.870  0.429  11  0.097  0.212  0.073  0.118  -  -  12  0.043  0.102  0.003  0.032  -  -  0pen+  0.116  0.170  0.077  0.110  1.017  0.735  13  0.053  0.072  0.022  0.054  -  -  14  0.105  0.058  0.024  0.035  -  -  15  0.058  0.088  0.029  0.028  -  -  C1 uster+  0.072  0.073  0.025  0.039  -  -  Stand Avg  0.177  0.182  0.085  0.101  0.850  0.648  ;  * +  New tree Average for position of trees in stand  - 178 -  Table 16.  Average No. of pupae per f a s c i c l e by tree, branch type and horizontal crown position, 1974.  Tree  Main Branch  Side Branch  No.  1 nner  Mid  Outer  1 nner  Mid  Outer  1  0.000  0.039  0.096  0.008  0.031  0.075  2  0.000  0.000  0.146  0.082  0.097  0.319  3  0.042  0.116  0.281  0.167  0.031  0.222  4  0.164  0.199  0.217  0.093  0.133  0.127  0.051  0.088  0.185  0.087  0.073  0.186  5  0.133  0.264  0.382  0.271  0.387  0.635  6  0.111  0.166  0.157  0.258  0.136  0.210  7  0.054  0.078  0.144  0.039  0.192  0.385  8  0.049  0.056  0.086  0.026  0.070  0.079  0.087  0.141  0.192  0.148  0.196  0.327  9  0.102  0.036  0.050  0.098  0.142  0.085  10  0.042  0.025  0.106  0.133  0.065  0.223  11  0.033  0.031  0.046  0.100  0.135  0.127  12  0.045  0.024  0.031  0.139  0.101  0.131  0.055  0.029  0.059  0.117  0.111  0.141  13  0.048  0.000  0.030  0.063  0.035  0.029  14  0.000  0.000  0.021  0.059  0.089  0.055  15  0.043  0.010  0.025  0.125  0.069  0.154  C1uster+  0.030  0.003  0.025  0.082  0.064  0.079  Stand Avg.  0.058  0.070  0.121  0.111  0.114  0.190  1nter ior+  Edge+  0pen+  +  Average for position of trees in stand  - 179 -  Table 17-  Average No. of eggs per f a s c i c l e by tree, branch type and horizontal crown position,  Tree  Main  Branch  197*+ -  Side  No.  Inner  Mid  Outer  1  —*v  -  -  2  0.243  0.375  0.484  0.622  0.440  0.381  3  0.236  0.260  0.49**  0.591  0.5**6  0.693  4  0.502  0.890  0.521  0.446  0.817  0.280  0.327  0.508  0.500  0.553  0.601  0.451  5  0.499  0.798  0.605  0.521  0.627  0.3*»9  6  0.292  0.627  0.902  0.401  0.706  0.689  7  0.451  0.813  0.91 1  0.644  1.030  0.637  Edge+  0.414  0.746  0..806  0.•  0.788  0. 558  9  0.630  0.798  0.•  0. 566  0.435  0.663  10  0.686  1.065  1..096  0..558  1. 106  1.020  11  0.822  1.186  1..054  0.•  0. 613  0. 599  0pen+  0.713  1.016  0..902  0..574  0.718  0.761  Stand Avg.  0.485  0.757  0..736  0..550  0.702  0. 590  1nter ior+  Inner  Branch  -  Mid  -  Outer  -  8  556  No samples taken. +  Average for position of trees in the stand.  552  598  - 180 -  Table 18.  Average No. of prewinter larvae per f a s c i c l e by tree, branch type and horizontal crown position, 1974.  Tree  Main  No.  1 nner  1  0.749  2  Branch Mid  Side  Branch  Outer  1 nner  Mid  Outer  0.254  0.608  0.274  0.235  0.365  0.407  0.371  0.475  0.184  0.280  0.310  3  0.345  0.120  0.232  0.151  0.129  0.243  4  0.169  0.271  0.258  0.169  0.193  0.339  0.417  0.254  0.393  0.194  0.209  0.314  5  0.618  0.252  0.347  0.126  0.038  0.266  6  0.153  0.979  0.252  0.126  0.451  0.186  7  0.168  0.479  0.113  0.131  0.228  0.147  8  0.579  0.627  0.808  0.333  0.436  0.741  Edge+  0.379  0.584  O.38O  0.179  0.288  0.335  9  0.912  0.451  0.506  0.189  0.088  0.250  10  0.197  0.210  0.314  0.131  0.260  0.393  11  0.038  0.241  0.150  0.122  0.169  0.162  12  0.071  0.131  0.378  0.129  0.057  0.266  0pen+  0.304  0.258  0.337  0.143  0.143  0.205  Stand Avg.  0.367  0.449  0.362  0.172  0.214  0.306  1 nter ior+  +  Average for position of trees in the stand.  - 181 -  T a b l e 19-  A v e r a g e No. o f p o s t w i n t e r l a r v a e p e r f a s c i c l e by t r e e , b r a n c h t y p e and h o r i z o n t a 1 c r o w n p o s i t i o n , A p r i l 1975.  Tree  Main  No.  1 nner  1  0.465  2  Branch  Mid  Side Outer  1 nner  0.219  0.417  0.289  0.265  0.216  0.049  0.065  0.164  0.057  0.159  0.143  3  0.024  0.157  0.114  0.068  0.118  0.250  4  0.021  0.204  0.252  0.231  0.121  0.253  0.140  0.161  0.237  0.161  0.166  0.215  5  0.055  0.343  0.556  0.282  0.076  0.381  6  0.149  0.293  0.292  0.151  0.169  0.141  7  0.000  0.133  0.610  0.070  0.169  0.152  8  0.209  0.523  0.604  0.368  0.692  0.685  Edge+  0.103  0.323  0.515  0.218  0.276  0.340  9  0.079  0.102  0.393  0.076  0.245  0.052  10  0.103  0.078  0.221  0.065  0.243  0.411  11  0.000  0.045  0.227  0.153  0.211  0.271  12  0.020  0.054  0.055  0.041  0.076  0.189  0pen+  0.050  0.070  0.224  0.084  0.194  0.231  13  0.071  0.056  0.034  0.076  0.096  0.044  14  0.137  0.104  0.074  0.026  0.067  0.081  15  0.056  0.040  0.078  0.070  0.071  0.124  C1 u s t e r +  0.088  0.067  0.062  0.057  0.078  0.083  Stand Avg.  0.096  0.161  0.273  0.135  0.185  0.227  1 nter ior+  +  Average f o r p o s i t i o n o f trees  i n the stand.  Mid  Branch Outer  - 182 -  Table 20.  Average No. of pupae per f a s c i c l e by tree, branch type and horizontal crown position, June 1975•  Tree  Main  Branch  Side Branch  No.  1 nner  Mid  Outer  1 nner  Mid  Outer  1  0.085  0.065  0.124  0.126  0.050  0.160  2  0.071  0.074  0.013  0.051  0.230  0.216  3  0.232  0.139  0.318  0.030  0.085  0.115  4  0.165  0.250  0.099  0.040  0.115  0.187  0.138  0.132  0.138  0.062  0.120  0.169  5  0.000  0.458  0.167  0.073  0.086  0.164  6  0.000  0.012  0.058  0.098  0.059  0.221  7  0.052  0.100  0.042  0.000  0.273  0.189  8  0.032  0.040  O.O83  0.084  0.102  0.305  Edge+  0.021  0.152  0.087  0.063  0.130  0.220  9  0.365  0.035  0.111  0.031  0.030  0.192  10  0.000  0.037  0.149  0.057  0.129  0.430  11  .0.000  0.01 1  0.208  0.026  0.286  0.040  12  0.000  0.000  0.009  0.000  0.026  0.071  0pen+  0.091  0.021  0.119  0.028  0.117  0-183  13  0.000  0.000  0.066  0.007  0.093  0.061  14  0.000  0.000  0.072  0.023  0.008  0.072  15  0.033  0.000  0.055  0.022  0.005  0.055  C1 uster+  0.01 1  0.000  0.064  0.017  0.035  0.063  Stand Avg.  0.069  0.082  0.105  0.045  0.091  0.165  1 nter ior+  +  Average for position of trees in the stand.  -  Table 21 .  183 -  Average No. of eggs per f a s c i c l e by tree, branch type and horizontal crown pos it ion,  Tree  Main  Branch  1975. Side  No.  1 nner  Mid  Outer  1 nner  1  0.803  1.108  0.999  2  0.460  0.758  4  0.863  Branch Mid  Outer  0.729  0.575  0.669  0.397  0.484  0.264  0.460  0.551  0.706  0.544  0.599  0.424  0.709  0.806  0.701  0.586  0.478  0.518  5  0.553  0.635  1 .185  0.833  0.529  0.982  6  0.553  0.946  0.807  0.550  0.477  0.819  8  1.272  0.848  0.876  0.906  0.721  0.584  Edge+  0.793  0.808  0.956  0.763  0.576  0.795  9  1.312  1.266  O.9I7  1.181  1.013  0.930  12  1.095  1.380  0.134*  0.536  0.472  0.277  Open+  1.203  1.323  0.525  O.858  0.742  0.603  Stand Avg.  0.861  0.936  0.753  0.720  0.582  0.643  1nter ior+  *  Low counts as this contained current year shoots.  +  Average for position of trees in the stand.  - 184 -  Table 22. Average No. of insects per  f a s c i c l e by crown level and exposure.  Exposed Crown  Shaded  Lower  Mid  Upper  Lower  Mid  Upper  Pupa (1974)  0.095  0.112  0.096  0.117  0.152  0.092  Egg  0.537 0.301  0.705 0.429 0.206  0.806  0.619  0.678  0.277  0.473 0.236  0.140  0.165  0.307 0.136  0.319 0.207  0.115  0.119 0.862  0.051  0.091  0.610  0.846  0.071 0.921  Stage:  Larva^  Larva^O'975) 0.222 Pupa 0.108 0.518  Egg  0.738  Table 23. Average No.; of insects per f a s c i c l e by crown level and branch type. Main Branch Crown  Side  Branch  Lower  Mid  Upper  Lower  Mid  Upper  Pupa (1974)  0. 078  0. 097  0. 074  0. 134  0.,167  0. 114  Egg  0. 480  0. 672  0. 826  0. 531  0.,652  0. 659  Larva^  0. 323  0. 538  0. 316  0. 215  0.,198  0. 279  La 1 ^ ( 1 9 7 5 ) 0. 218  0. 177  0. 134  0. 169  0.,165  0. 213  Pupa  0. 091  0. 113  0. 047  0. 068  0..093  0. 143  Egg  0. 630  0. 842  1. 077  0. 498  0..742  0. 705  Stage:  Table 2 4 . Average^No. of insects per f a s c i c l e by branch type and exposure. Main  Branch  Side  Branch  Stage  Exposed  Shaded  Exposed  Shaded  Pupa (1974)  0.083  O.O83  0.119  0.158  Egg  0.709  0.609  0.657  0.571  0.418  O.367  0.253  0.208  0.193  0.186  0.160  0.179  Pupa  0.108  0.062  0.120  0.080  Egg  0.767  0.933  0.645  0.652  Larva Larv  3  ait  (1975)  - 185 -  Table  Average number of f a s c i c l e s per 15 cm branch section by tree and c o l l e c t i o n period.  25.  -  Tree No.  Average No. of Fascicles/15~cm branch section at P  (1974)  E '  (197^)  L  P (1975)  3  Avg.  9.9  9.8  12.3  10.6  12.7  10.5  10.1  12.1  11.3  10.7  12.5  10.2  9.4  11.2**  10.8  4  11.6  11.1  10.2  10.5  11.7  11.0  5  11.1  9.4  8.1  7.6  10.0  9-2  1  10.4  2  11.3  3  6  8.7  9-9  7.9  10.6  12.9  10.0  7  13-9  12.8  13.2  7-5  11.7  11.8  8  14.2  -  14.4  14.1  9  12.6  13.7  9.9  9.5  12.0  11.4  10  12.1  12.5  11.2  12.3  13.8  12.4  11  15-9  17.7  16.1  16.0  16.3  16.4  12  15.4  -  15-9  16.2  17.8  16.3  15  17.1  -  -  13.2  16.7  15.7  16  12.5  -  -  10.4  16.1  13.0  17  16.0  -  -  13.8  19.5  16.4  Avg.  12.9  12.5  11-5  11.3  12.4  12.1  *  No samples taken  **  Different tree  15.2  12.6  - 186 -  Appendix 5.  Fig. I.  Frequency d i s t r i b u t i o n of f a s c i c l e s per 15-cm  Fig. II.  branch section.  Relationship between variance (S ) and mean (x) of f a s c i c l e per 15 cm branch section by tree. -  - 186a  2  i*  6  8  1 0 1 2  Frequency d i s t r i b u t i o n  _..  ,1 9  :  15-cm  1 6 1 8  section  by  per  22  2 6 2 8  2 k  15"cm  branch  ' 15  1  13  between v a r i a n c e  branch  2 0  of f a s c i c l e s  • 11  Relationship per  14  -  (S ) and  tree.  section.  — 17  mean  (x) o f  X  fascicle  

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