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Some factors affecting colonization and distribution of bark-beetles within selectively logged areas Reid, Robert William 1953

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SOME FACTORS AFFECTING COLONIZATION AND DISTRIBUTION OF BARK-BEETLES WITHIN SELECTIVELY LOGGED AREAS by ROBERT WILLIAM REID A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS We accept this thesis as conforming to the standard required from candidates f o r the degree of MASTER OF ARTS Members of the Department of Zoology THE UNIVERSITY OF BRITISH COLUMBIA APRIL, 1953 AC KNOWLEDGMENTS A considerable portion of the design and experi-mental procedure f o r this investigation was drawn up by Mr., C-.R.Hopping, O f f i c e r i n Charge of the Forest Zoology Lab-oratory, Calgary, Alberta. I wish to express my sincere appreciation f o r this help and for his continued support and interes t during the course of the in v e s t i g a t i o n . I am deeply indebted to Dr. K. Graham f o r his d i r e c t i o n and encouragement during the analyses of the f i e l d data and f o r guidance i n the preparation of the manuscript. Grateful acknowledgment i s made to Dr. W.A.Clemens, Professor G.J. Spencer, and Dr. R.A.Larkin f o r t h e i r a s s i s -tance i n the f i n a l preparation of the manuscript. The project on which this thesis i s based was carried out under the auspices of the D i v i s i o n of Forest Biology, Science Service, Dominion Department of Agriculture. Dr. M.L. Prebble, D i v i s i o n Chief, has kindly allowed i t s use. TABLE OF CONTENTS Page INTRODUCTION ' 1 BIOLOGY OF IPS PINT SAY 4 D i s t r i b u t i o n and hosts 4 Description . . . 4 L i f e cycle 6 Gallery pattern and habita 8 MATERIAL AND METHODS H Description of region 11 Description of f o r e s t r y experiment 12 Sampling coverage 15 F i e l d techniques 13 S t a t i s t i c a l techniques 20 EXPERIMENTAL RESULTS , • 21 Slash diameter and number of attacks 21 Frequency d i s t r i b u t i o n of attacks . . . 22 Inter-block relationships 25 DISCUSSION 27 Relationship between number of attacks on the slash and the diameter class of the slash . . . 27 Frequency d i s t r i b u t i o n of attacks within the slash 34 Relationship between the abundance of bark-beetles and the method of cutting 4Q SUMMARY AND CONCLUSIONS . . . 4 7 LITERATURE CITED „ Q APPENDIX I 51 1 SOME FACTORS AFFECTING COLONIZATION AND DISTRIBUTION OF BARK-BEETLES WITHIN SELECTIVELY LOGGED AREAS INTRODUCTION Forest insect populations, l i k e many other animal populations, are not uniformly d i s t r i b u t e d throughout an area but are found i n various degrees of concentration r e g i o n a l l y and l o c a l l y . Bark-beetles constitute a major group of economically important forest insects and the causes of t h e i r variable concentrations are only p a r t i a l l y understood. Among the important circumstances with which variable bark-beetle populations are associated are those encountered i n forest stands undergoing cutting practices. In such stands, the conditions a f f e c t i n g bark-beetles vary according to diff e r e n t cutting methods which coincidentally produce d i f f e r e n t quantities of food i n the form of slash, and expose that food, as well as the environment generally to altered micro - and meso - climates. 2 The present i n v e s t i g a t i o n was undertaken to determine and explain some of the major factors underlying the v a r i a b i l i t y i n concentration of ce r t a i n bark-beetles i n a forest stand cut i n certa i n selected ways. An investigation of this' nature may be carried out i n an area chosen f o r this purpose alone, or may be coordinated with a programme already designed f o r s i l v i c u l t u r a l purposes. There are advantages and disadvantages either way. The requirements for entomological experimentation are not necessarily best provided by the experimental design which is adequate f o r s i l v i c u l t u r a l purposes. On the other hand, the results from such a coordinated study carry the weight of authenticity f o r representing an actual f o r e s t r y condition, .and not merely a hypothetical case. In addition, the use of the materials provided by a s i l v i c u l t u r a l study make possible an entomological study which would otherwise be too c o s t l y of time and e f f o r t . Indeed, one of the chief obstacles to this type of study, heretofore, has been the lack of s e l e c t i v e l y cut' stands. In 1952 the Dominion Forest Service i n i t i a t e d studies on selective cutting of lodgepole pine (Plnus contorta Dougl.) i n the f o o t h i l l s region of Alberta. The opportunity was here presented for getting the special f o r e s t r y conditions f o r the desired entomological study. 3 The entire entomological Investigation, of which this study i s a part, had a broad basis. Ultimately, i t i s desired to know something of the make-up of the insect com-plex associated with stands s e l e c t i v e l y cut i n di f f e r e n t ways, to learn something of the factors responsible f o r the vari a t i o n of concentration, and to observe the eff e c t of the insect population on the fo r e s t . The present investigation i s an i n i t i a l study to determine the manner'in which the bark-beetles disperse within newly logged regions, and to relate t h e i r type of dispersal with the factors common to the environment. The insect complex was made up c h i e f l y of Scolytids, Cerambycids, and Buprestids. Among the species, Ips p i n i Say. formed the most important component and the one which pro-vided the most suitable data for a n a l y t i c a l study. Accord-i n g l y the data concerning this species form the basis f o r the conclusions arrived at i n this study. ' 4 THE BIOLOGY OF IPS PINI SAY Di s t r i b u t i o n and hosts This species is widely d i s t r i b u t e d throughout the range of the Boreal Forest. It i s generally considered a secondary forest insect pest requiring that the host tree be previously weakened by some factor which reduces vigor and growth. The chief hazard ,from th i s bark beetle arises from population build-ups i n fresh slash and subsequent severe but shortlived attacks on trees i n the surrounding stand. Host trees are most commonly pines, but spruce and l a r c h have also been reported as being attacked. The host tree i n the region of this i n v e s t i g a t i o n was lodgepole pine. Description of Ips p i n i Say The egg, l a r v a l , pupal stages are described by Clemens (1916) as follows: "The egg is e l l i p t i c a l i n shape and about 0.75 mm. long. I t has a smooth, g l i s t e n i n g surface, pure white i n color." "The larva when i t hatches i s a small legless grub 1 mm. i n length. The mature larva reaches a length of 4 mm. The body i s pure white, often tinged with reddish 5 brown due to food i n the alimentary canal. The head is strongly c h i t i n i z e d and i s l i g h t brown i n color." Swaine (1918) describes the adults as; "Length, 3.5 mm. to 4.2 mm.; the. front convex and coarsely granulate; the pronotum s l i g h t l y but evidently longer than wide, f i n e l y punctured behind, the punctures smaller towards the middle l i n e , f i n e l y , closely, acutely, subconcentrically asperate i n front, the sides s l i g h t l y , arcuately narrowed on the basal three-fourths, emarginately narrowed on the cephalic fourth and narrowly rounded i n front; the e l y t r a l s t r i a e usually s l i g h t l y or not at a l l impressed, with the s t r i a l punctures small, the sutural s t r i a e u s u a l ly but l i t t l e more evident, the d e c l i v i t y with the 2nd and 3rd teeth acute and s i m i l a r . The male has the front more coarsely granulate, and the 3rd d e c l i v i t a l tooth longer, stout, and s l i g h t l y curved. There are frequent variations i n nearly a l l the external characters; the pronotal punctures vary from moderate i n size to small, and nearly obsolete on the middle l i n e ; the sides are sometimes d i s t i n c t -l y angled at the cephalic fourth; the sutural st r i a e and less often the other d i s c a l s t r i a e are sometimes d i s t i n c t l y impressed, and the , e l y t r a l punctures are sometimes moder-ate l y coarse." 6 L i f e Cycle Ips p i n i Say overwinter as old adults, young adults, and less commonly as pupae and larvae. The seasonal development i s i l l u s t r a t e d diagrammatically i n Figure 1. The old mature adults attack t h e i r new host .about the middle of May. These attacks are commonly referred to as " s t r i k e s " . They e s t a b l i s h one brood which develops to mature adults by the f i r s t of July. These new adults then e s t a b l i s h broods which require the remaining part of the sea-son to complete th e i r development, overwintering l a r g e l y as young adults. The o r i g i n a l parent stock dies during the summer while the progeny, parents of the July brood, over-winter as old adults. The young adults which have overwintered e s t a b l i s h two broods during the summer and i t is suspected they die soon a f t e r the second brood has been established. The f i r s t brood is established around the middle of May, adults emerg-ing by the end of June. These new adults then e s t a b l i s h a brood i n July and overwinter as old adults. The progeny require the remainder of the season to develop and pass the winter l a r g e l y as young adults, and a few pupae and larvae. The second brood established by the o r i g i n a l overwintering young adults, matures and spends the winter as young adults, with some larvae and pupae. SEASONAL DEVELOPMENT OF IPS PINI Fit*. I. O V E R W I N T E R I N G F O R M O V E R W I N T E R I N G F O R M O L D A D U L T S Y O U N G A D U L T S P U P A E ^ Y O U N G A D U L T S L A R V A E P U P A E Y O U N G A D U L T S > LARNAE P U P A E Y O U N G A D U L T S O L D A D U L T S L A R V A E > P U P A E Y O U N G A D U L T S O L D A D U L T S L A R V A E > P U P A E Y O U N G A D U L T S A D U L T S 8 The overwintering pupae e s t a b l i s h broods i n July. These broods develop, overwintering as young adults, pupae, larvae. The parents overwinter as old adults. The lower diagram i n Figure 1 i l l u s t r a t e s the pre-sence of various stages throughout the season. Gallery Pattern and Habits The method of ga l l e r y establishment of Ips p i n i has 'been described by Clemens (1916). The i n i t i a l entry hole into the bark i s made by' the male, who burrows a c y l i n -d r i c a l antry hole at an oblique angle through the bark to the sapwood surface and constructs a triangular to oval nuptial chamber. See Figure 2 and 3. When the nuptial chamber has been completed, several females enter and con-struct i n d i v i d u a l secondary or egg g a l l e r i e s . This species i s polygamous, the number of female g a l l e r i e s to each nuptial chamber varying from two to f i v e , the most frequent being three. Mating takes place within the nuptial chamber. The female g a l l e r i e s radiate from the nuptial chamber as indicated i n Figure 2. As the female elongates her gallery, she excavates minute egg niches, placing an egg i n each niche,, and then packs i n sawdust u n t i l the opening i s even with the wall of the ga l l e r y . The eggs are l a i d at c l o s e l y spaced i n t e r v a l s , commonly along both sides of the secondary ga l l e r y . F i g u r e 2 Bark sample showing p a r t i a l l y completed s e c -ondary g a l l e r i e s of Ips p i n i A. N u p t i a l chamber B. Secondary g a l l e r y w i t h egg n i c h e s 5'igure 5 Showing g a l l e r i e s of Ips p i n i upon the wooa s u r r a c e , l a r v a l g a l l e r i e s (c) a p p r o x i m a t e l y 14 days o l d . The nuptial chamber and female secondary-g a l l e r i e s are kept clear of frass and boring dust. The f e -males remove this material by rotating t h e i r bodies within the g a l l e r y and r e t r e a t i n g backward to the nuptial chamber. The male then pushes this material out the entry hole where the accumulating brown boring dust becomes conspicuous. The larvae, on hatching from the eggs, commence to mine at r i g h t angles from the secondary g a l l e r y . These l a r v a l mines may take a serpentine course, increasing i n size as the larvae develop, and winding through the subcortex and cambium, l i g h t l y engraving the sap wood. On completion of l a r v a l development pupal chambers are constructed at the ends of the l a r v a l galleries.. The pupal chamber i s sealed off with boring dust and generally^forms a s l i g h t cradle within the sap wood. • Young adults feed extensively under the bark, often o b l i t e r a t i n g the o r i g i n a l g a l l e r y pattern, often caus-ing the outer bark to shed i n large patches. Young adults change i n color from pale yellow to black as they reach maturity. Exact figures are not available on the duration of the egg, l a r v a l , , pupal or adult stages, but great d i f f -erences are known to r e s u l t from variations i n temperature and humidity within the g a l l e r i e s . Broods established i n 11 slash, i n warmer exposed locations mature more .rapidly than those i n slash which is located i n shaded, cooler locations. In New York State, Clemens (1916) records eggs hatching i n f i v e days at a temperature of 69° P. Pupae were found to mature i n f i v e days. Within the experimental area, i n the present investigation, pupae were observed on June 16th with-i n g a l l e r i e s established May 12th. The l a r v a l period varied from 20 - 30 days. The f i r s t young or teneral adults were observed June 25th and required fspom two weeks to a month to mature. The overwintering habits of Ips p i n i appear to vary i n d i f f e r e n t regions., In New York State, Clemens (1916) records the bulk of the population overwintering as adults under the bark while Dodge (1938) i n Minnesota reports that adults overwinter i n the l i t t e r at the base of brood trees. Duff samples and bark samples taken i n early spring during this investigation revealed overwintering adults, pupae, and a few larvae under the bark and adults i n duff at the base of the infested tree. The larger part of the population appeared to overwinter beneath the bark. MATERIALS AND METHODS Description of Region The experimental area of this study i s i n the 12 region termed by Halliday (1937), the »B. 19 or f o o t - h i l l s section" and is bordered on the west by the Sub-Alpine forests of the Rocky Mountains and on the east by the B. 18 or Mixed-wood section of the Boreal f o r e s t . The elevation of the whole F o o t - h i l l s section varies from 3000 to 5000 feet ele-vation; that of the experimental area is about 3,500 fe e t . Halliday (1937) describes the B. 19 region as presenting a rough and broken topography, descending eastward to the plains region i n a series of somewhat flat-topped plateaux, much dissected by sharply cut r i v e r v a l l e y s . The mature s o i l type is podsolic, overlying Mesozoic and Ter-t i a r y sedimentary bed-rock. The region i s an ecotone con-d i t i o n between' the Boreal and Sub-Alpine fo r e s t s , having been greatly influenced by f i r e which has encouraged the growth of lodgepole pine which i s subcliraax dominant, mixed with white and black spruce. The white spruce, i f not prevented by f i r e , eventually becomes the dominant i n the climax form-ation. Aspen and white bi r c h are next i n abundance with black spruce and tamarack dominating swampy areas. Balsam f i r i s replaced by alpine f i r . No'g;ackpine occurs. Description of Forestry Experiment The Calgary branch of the Dominion Forest Service established nine 10-acre blocks within the experimental area. 13 The design of the project i s i l l u s t r a t e d . i n Appendix I. The experimental area i s located approximately 20 miles south west of Rocky Mountain House, Alberta, i n a pure stand of even aged (84 years) lodgepole pine. This p a r t i c u l a r region i s very f l a t with no topographic b a r r i e r s . Each block was cut i n a d i f f e r e n t manner. A l l u t i l i z a b l e material down to a 3-g- inch, diameter -was removed and marketed, the object of the Forestry department being to determine what happens to the residual stand on each block regarding growth, regeneration, windthrow, insect attacks and disease. The i n d i v i d u a l blocks were treated as follows: Block I - Heavily thinned from below reducing the number of commercial stems from 664 to 300 per acre. Dom-inant trees remain. Block II - Heavily thinned from above reducing the number of commercial sterns from 698 to 300 per acre. Sub-dominant and suppressed trees remain. Block I I I - Sanitation cut - a l l dying, deformed, suppressed trees removed. Block IV - Merchantable trees cut to a diameter l i m i t of 6.5 inches, reducing the number of stems from 697 to 521. MAP SHOWING EXPERIMENTAL DESIGN SEE APPENDIX "lb-Block V - Uncut cont r o l . Block VI - A l l merchantable volume removed except 10 seed trees per acre. Block VII - Clear cut. Block VIII - Shelterwood cutting, 70 crop trees per acre removed. Block XX - Patch logging, c i r c u l a r areas, 50 foot diameter clear cut.' Sampling Coverage It was considered that the experimental procedure would be such that f i e l d data would y i e l d information on: (1) the endemic population of bark beetles prior to logging, (2) the concentration of attacks within each cutting area, (3) the t o t a l population of bark beetles produced i n each cutting area. Under the supervision of members of the Dominion porest Service, blocks I, I I , IV, VI, VIII, IX were logged i n the late f a l l and winter of 1951 by a private operator. Blocks III and VII were logged i n the spring and summer of 1952. It had been anticipated e a r l i e r that the entire nine blocks would be included i n the entomological investigation. However, the f i n a l study included only blocks I, I I , iv, VI, VIII: i t was found that block IX did not lend i t s e l f properly 16 to the sampling techniques employed so i t was not included. Blocks I I I and VIII were not f i n i s h e d i n time to he included. It was f e l t however, that the f i v e remaining blocks would s t i l l constitute a formidable area f o r the personnel avail-' able f o r study purposes and would y i e l d s u f f i c i e n t data to give some understanding of the factors involved i n the build-up of bark-beetle populations. One of the main d i f f i c u l t i e s encountered by a l l workers on populations i n b i o l o g i c a l communities, is the very large number of samples required, a point exemplified i n this current research where the enormous number of detailed records considered essential for the project, was a l i m i t i n g factor i n time and e f f o r t of the personnel involved. The most common and acceptable method of sampling bark beetle populations en t a i l s peeling the bark and expos-ing the insect g a l l e r i e s , a slow rather laborious procedure. A number of r e s t r i c t i o n s associated with this p a r t i c u l a r i n -vestigation fufcther slowed down the rate of sampling, these being: - (1) Necessity for a record of not only the s t r i k e s , but also a complete record of a l l insect stages and forms found under-the bark. (2) the need for complete records required that the bark be peeled very c a r e f u l l y so as not to destroy any of the insects. (3) Necessity f o r at least two population samples, one i n the early summer and the other i n the f a l l . (4) Shortness of the season and a v a i l a b i l i t y 17 of s u f f i c i e n t men to carry out the sampling. Because of the requirements as to d e t a i l , i t was necessary to r e s t r i c t the coverage to a minimum which would s t i l l meet the demands of s t a t i s t i c a l analysis. The endemic population was determined i n the early spring before the bark beetles became act i v e . This i n -volved sampling i n two environments; (1) the standing trees (2) the duff below infested trees. The endemic population overwintering under the bark of l i v i n g trees was determined as follows: Two 30-chain s t r i p s , running parallel-and 1 chain apart, were cruised using l/2 chain t a l l y s t r i p s . A l l green or fading infested trees were recorded i n f i e l d books. Each tree within the transect was examined f o r evidence of bark beetles. Ten of the known infested trees, 5 per s t r i p , were selected randomly f o r anal y s i s . To determine i f any bark beetles overwinter i n the duff at the base of infested trees, duff samples were taken from under these trees and also from below trees known to be non-infested. The populations within the experimental area were determined within permanent p l o t s . A l l blocks were handled i d e n t i c a l l y ; by using a s t a f f compass and a 100-foot s t e e l tape, ten c i r c u l a r plots 50 feet i n diameter were established 18 i n each block. Appendix I i l l u s t r a t e s the lo c a t i o n of the plots within each block. The plots are l e t t e r e d A to F and IF to 2 . F i e l d Techniques The survey of endemic populations required one week, being completed by May 19th. ,Ten inf e s t e d trees were examined. Bark was c a r e f u l l y peeled from one foot sections, • marked every three feet along the main stem. The following points were recorded: - Diameter of the 1-foot section; numbers of bark beetles by species and stages of each; number of old and new s t r i k e s . From each tree found i n the i n i t i a l cruise to contain bark beetles was recorded the Dbh, crown c l a s s i f i c a t i o n ( = suppressed, intermediate, co-dominant, dominant) and the condition of the crown. The duff samples, each one foot square, were collected as part of the endemic survey and were selected as follows once per month from infested and uninfested trees: A. 4 samples adjoining the base. B. 4 samples half way between base and v e r t i c a l projection of the crown. C. 4 samples at the v e r t i c a l projection of the crown. The bark beetle populations f o r each block were 19 sampled i n the middle of July and also again i n September. In each c i r c u l a r plot, ten separate foot-long sections of slash were marked, diameters recorded, and each piece record-ed i n t h e ' f i e l d book for that block; these pieces were selected randomly. In addition, on 6 plots i n each block, one tree-length piece of slash was marked every three' feet into 1 foot sections. To record populations i n the stumps, 5 were marked i n plots A to P i n c l u s i v e . The stumps i n each plot were marked and top and bottom diameters recorded. Therefore, i n each plot there were sampled 100 pieces of •slash, 30 stumps and 6 tree-length pieces of slash. The stumps were sampled only once, during the l a t t e r part of August. A l l pieces of slash and a l l stumps within each 50 foot diameter c i r c u l a r plot were measured f o r t o t a l surface area of bark. From each piece of slash and each stump the follow-ing information was recorded. (1) t Diameter (2) Bark thickness (3) Bark c h a r a c t e r i s t i c (4) D i r e c t i o n i n which slash was l y i n g (5) Position of slash, i;.e. a e r i a l or on ground (6) Shaded or exposed (7) Number of strikes by species on each side (8) Number of adults, larvae, pupae on each side by species (9) Number of predators and parasites. A l l insect material was preserved i n 70^ alcohol. 20 S t a t i s t i c a l techniques The problem of bark-beetle d i s t r i b u t i o n was approached from the aspect of determining the nature of the var i a t i o n i n population density on a l i n e a l foot basis. To determine i f each l i n e a l foot or unit of measurement was exposed to i n f e s t a t i o n i n a random manner, a single diameter class was selected. The 3.5 inch to 3.9 inch class was found to represent most consistently, both in,number of pieces and average s t r i k e s , the frequency d i s t r i b u t i o n within the area. As pointed out by Wadley (1950), there i s a gen-era l b e l i e f that i f a population distributes i t s e l f over a number of units at random, the d i s t r i b u t i o n of numbers per unit, w i l l approximate a Poisson s e r i e s . Deviations w i l l i n -dicate f a i l u r e of randomness. Because there i s nearly always a departure from the Poisson type of d i s t r i b u t i o n i n b i o l o g i c -a l data, due to excessive variance and dispersion, several other types of empirical d i s t r i b u t i o n s have been used. Three dis t r i b u t i o n s were tested: Poisson, negative binomial, and Meyman's contagious d i s t r i b u t i o n . In Neyman's contagious d i s t r i b u t i o n , the expected proportion of units with zeros, was f i r s t calculated. Succ-essive terms were then computed from the preceding ones. The expression f o r proportion of zeros was: Fi = e^'('-«"^0 21 A s i m p l i f i e d version f o r computing the expression f o r terms other than zero was; 5n n "n-K Kf In computing the values for the negative binomial d i s t r i b u t i o n a s i m p l i f i e d version was suggested by Dr. K. Graham. In place of working out each i n d i v i d u a l expression the s i m p l i f i e d expression was as follows: This describes a l l terms above P» The value f o r which was obtained from the following: Pm • ^  An analysis of the average number of strikes f o r each block was done to test the significance of the various means. This involved a test on the Analyses of Variance between a Group of Means, the group i n this case being composed of the means of the f i v e blocks. EXPERIMENTAL RESULTS Relationship of Slash Diameter to Strikes The mean number of strikes i n each diameter class and i n each block is i l l u s t r a t e d i n Table I, on a per square foot of bark surface basis. The percentage of pieces i n each 22 diameter which were attacked, the t o t a l percentage of a l l pieces attacked per block and the mean diameter of the slash i n each block i s also included. Frequency D i s t r i b u t i o n of Strikes Observed d i s t r i b u t i o n s are compared with three d i f f e r e n t t h e o r e t i c a l d i s t r i b u t i o n s i n the 5 blocks. These are presented i n Table H. " Distributions i n eachrblbck are si m i l a r . In a l l cases a great deviation from the Poisson type of d i s t r i b u t i o n indicates non-randomness i n the d i s t r i -bution. P r o b a b i l i t i e s of conformity are also given i n Table I I . While the p r o b a b i l i t i e s are a l l low, there does appear to be a consistent difference between the types of d i s t r i b u t i o n , the Neyman's contagious type of d i s t r i b u t i o n i n a l l cases giving the best estimate of the actual situation.-TABLE I Relation of Strikes Per Square Foot of Bark Surface to Diameter of Slash Diameter Class BLOCK 2.0-2.4 2.5-2.9 3.0-3.4 3.5-3 .9 4.0-4.4 4.5-4.9 Total % of a l l slash diameters attacked i n each block 1.97 3.68 4.05 3.62 4.45 10.50 70 I I 0.348 0.820 1.04 1.70 2.72 5.2 50 IV 0.198 0.645 0.876 26 VI 2.38 1.19 1.89 2.88 3.29 58 VIII 0.935 3.17 1.84 2.22 4.05 Mean 1.2 1.6 2.0 2.0 3.1 5.8 % of pes available to a t t a -ck which ¥i^ ere attacked 26.6 46.2 46.0 49.8 65.8 93.0 55 Mean diameter of slash 3.4-.209 3.4-.202 3.4-.114 3.7-.149 3.8-.119 to TABLE II D i s t r i b u t -ion Tested Actual H Neyman's ^ Contagious o Negative S Binomial m Poisson Total Nos . 34 Di s t r i b u t i o n of Frequency of Bark-Beetle "Strikes/Lineal f t . of Slash Frequency of Strikes • (Deviations)' Expected Remai- Deviation proba-i—i Actual H Neyman's Contagious o Negative ^ Binomial Poisson •> Actual H Neyman's M Contagious § Negative ^ Binomial CO Poisson Actual Neyman's Contagious Negative o Binomial CQ Poisson H Actual HJ Neyman's > Contagious w Negative o Binomial 51 Pois son 0 1 2 3 4 5 6 nder Expect- DF b i l i t y No. of • times this frequency < occurred ed 11 3 4 2 1 •: 4 1 8 10.71 2.15 3.2 3.56 3.18 2.61 2.18 6.41 4.24 5 .53 6.4 5.89 4.86 3.87 3.03 2.34 1.80 .5.71 9.39 5 •11 1.03 3.59 6.23 7.34 6.42 4.5 2.6 2.18 122.75 6 less than.GL 12 8 6 2 0 3 1 1 12.25 5.49 4.81 3.34 2.10 1.26 0.73 3.02 7.93 5 .17 11.48 8.22 5.27 3.24 1.95 1.16 .07 1.61 16.20 5 less than.01 6.42 10.51 8.61 4.69 1.92 0.33 0.09 0.43 54.19 6 w it 31 3 1 0 3 1 — 0 29.64 3.21 2.82 1.75 0.89 0.41 -- 0.5 8.85 5 .12 27.95 5.95 2.48 1.21 .63 .34 0.5 14.01 5 less than. 05 22.19 '12.52 3.53 .66 .09 .01 0. 202.5 6 " .01 22 2 5 5 3 4 0 2 20.41 4.51 5.19 4.33 3.06 2.03 1.61 , 1.86 3.57 5 .61 16.5 9.48 5.93. 3.81 2.47 1.62 1.06 2.13 13.04 5 less than .05 7.35 12.97 11.47 6.75 2.98 1.06 0.31 0.11 1309.66 6 B .01 25 4 4 5 7 3 1 2 21.57 7.11 7.17 5.48 3.71 2.38 1.45 " 2.13 6.82 5 .24 17.97 11.91 7.68 4.91 3.13 1.98 1.25 2.17 12 .48 5 less than.05 8.57 15.28 13.63 8.11 3.62 1.29 0.38 0.13 117.38 6 " .01 25 Inter-block Relationship and Mean Number,of Strikes The mean number of strikes i n each block is i l l u s t r a t e d f o r a single diameter class i n Table I I I , and f o r a l l diameters i n Table IV. TABLE III . Number of S t r i k e s / l i n e a l Foot Within a Single Diameter Class 3.5"-3.9a , , - —— _ t Block Mean Standard Deviation I 3.5 3.67 II 1.65 1.95 IV 0.56 1.23 VI 1.77 2.34 VIII 1.78 2.19 TABLE IV Frequency of St r i k e s / L i n e a l Foot Within A l l Diameters--2" to 5.4" Block Mean Per Standard Total Pieces Block Deviation of Slash I 3.46 3.3 100 II 1.65 1.9 100 IV 0.68 1.2 100 VI 2.00 2.1 100 VIII 2.12 2.3 100 The apparent differences i n concentration of bark beetles i n each block as presented i n Table i v were tested f o r significance as shown i n Table V. The high F value revealed that the differences were not due to chance. 26 TABLE V Analysis of Variance Between Mean Number of Strikes i n Each Block Source of Variation Sum of Squares Mean Degrees about Appro- Square of . priate Mean Freedom 7.19 Between Blocks 7.19 1.80 4 51.5 495 Random Variation 51.3 .01 495 within Blocks Total 58.5 499 p = Mean sq. between Blocks F _ Mean sq. within Blocks x 495 = 17.3 27 DISCUSSION Relationship between Number of Attacks and diameter class of the slash Table I indicates a r e l a t i o n s h i p between the dia-meter of the slash and the frequency of attacks by Ips p i n i Say. The diameter classes of the pieces of slash within each block are represented with s i m i l a r frequency, tis shown i n Table VI. Moreover, i n a l l blocks the frequency d i s t r i b u t i o n of d i f f e r e n t diameter classes approximates a' "normal" d i s t r i b u t i o n , i n the s t a t i s t i c a l sense, i . e . symmetrical, with the greatest frequency i n the intermediate classes. This reduces the l i k e l i h o o d that the greater density of attack i n the larger diameter class might have been due to a greater surface area and greater a c c e s s i b i l i t y . TABLE VI D i s t r i b u t i o n of Diameters of Marked Slash within the Experimental Area Diameter Block Number Class I II IV VI VIII Total Total Inches No. Pes. i n each Dia. Class Number Area 2.0-2.4 8 5 2 0 0 15 1,142 Sq. 2.5-2.9 20 19 7 3 3 52 5,299 « 3.0-3.4 19 23 48 26 8 124 15,390 w 3.5-3.9 34 33 40 43 51 201 28,393 n 4.0-4.4 14 14 3 22 36 89 14,098 » 4.5-4.9 3 5 0 5 2 15 2,660 R 5.0-5.4 2 1 0 1 0 4 785 » 28 A cer t a i n diameter preference, on standing trees, f o r brood establishment i s shown by many di f f e r e n t species of bark beetle. Hopping and Be a l l (1948) observed during the Banff park outbreak of the mountain pine bark-bee t i e (Dendroctonus raonticoloe), that there appeared to be a. r e l a t -ionship between tree s u s c e p t i b i l i t y and tree diameter. Trees under 6 inches i n diameter were r a r e l y attacked and the degree of i n f e s t a t i o n varied d i r e c t l y with increasing diameters. In Sweden, Tragardh (1938) found that attacks by the spruce bark-beetle (ips typographus) decreased i n proportion to de-crease i n diameter of the tree i n an arithmetic series. The same author observed that attacks by the pine beetle (Blastophagus piniperda)varied by less than 4% within dia-meters ranging from 32 to 12 cms. However i n diameters below 12 eras, the attacks decreased very abruptly. Graham (1952) i l l u s t r a t e s graphically the sequence of bark-beetle attacks frequently occurring on yellow pine (Pinus ponderosa) and shows the r e l a t i v e p o s i t i o n occupied by the several species involved. Ips spp. attacks are confined to the upper portion of the main stem and the crown while Dendroctonus attacks extend from the base to the lower portion of the crown. Many bark-beetles are associated exclusively with the thick-barked lower portion of the stem, mostly of the Dendroctonus group; while other species remain i n the thin soft barked regions of the crown and branches, i . e . Pityophthorus, Pityogenes. 29 In general, bark-beetles are rather s p e c i f i c not only i n respect to kind of host tree but also as to the port-ion of the tree attacked. For example, c e r t a i n species con-f i n e t h e i r attacks to the basal portion of the stem, others to the main stem, others to the upper stem and s t i l l others to the branches. This consistency i n s e l e c t i o n of p a r t i c u l a r portions of a tree was pointed out by Beal (1945), who stated that bark-beetles entering slash usually occupy the same anatomical regions of a tree as they do i n standing trees. The underlying factors i n this discrimination by the beetles are not c l e a r l y understood, but correlated with d i f f e r e n t portions of a tree there are gross observable c h a r a c t e r i s t i c s such as diameter and bark character. It i s not suggested that diameter differences as such are distinguishable to the beetles, but diameter happens to provide a convenient and measureable index of the s t i l l unknown factors which may be primarily involved. A bark-beetle susceptible tree, as a u n i t , offers a choice of environment and i t i s apparent that c e r t a i n species are adapted to certain sections of that u n i t . A number of differences occur i n the inner and outer bark, correlated with diameter, the most e a s i l y recognized being thickness and structure, surface c h a r a c t e r i s t i c , color, and possibly odour. It i s one or a combination of these which determines the s e l e c t i v i t y by the bark-beetles. 30 Zolk (1938) r e f e r r i n g to the pine bark beetle of Europe (Biastophagus piniperda) relates diameter and density of attack to the bark thickness. Infestations ordin-a r i l y occur only i n that part of the log which has thick bark, density of i n f e s t a t i o n being proportional to the thickness of the bark. Biastophagus minor, on the other hand, prefers sections with smooth bark, as does also the weevil Pissodes  piniphilus H l i s t . He concludes that the condition of the bark influences the time, place and amount of i n f e s t a t i o n as well as the species present. Diameters are c l o s e l y related to bark thickness which i n turn governs to a considerable degree temperature and humidity of the subcortical region. Thick-barked regions ret a i n the high moisture content of the cambium and inner bark, preventing excessive desiccation. Beal (1943) found bark thickness by far the most important single f a c t o r which determines the difference between subcortical and a i r temperatures. The'same author (1934) i n the southern pine region of the United States found su b c o r t i c a l temperatures reached a l e t h a l maximum of 112° P i n exposed regions when a i r temperatures were 70° F. The surface c h a r a c t e r i s t i c s of the bark on the main stem are quite d i f f e r e n t from those found on the bark i n the smaller diameter but more r a p i d l y growing upper crown 31 region. Figures 4 and 5 i l l u s t r a t e this i n two photographs, one taken of hark well down from the crown and the other from the upper regions of the crown. The bark from the lower, section is thicker, with large hard' curled flakes while the bark from near the top i s very soft with thin t i s s u e - l i k e small flakes . It i s known that odours from fermenting inner bark and sapwood are an attractant to bark beetles and i t can be assumed larger diameter slash would release a greater quantity of these odours than smaller diameters. Where large and small diameters are l y i n g i n close proximity to each other there i s a strong p o s s i b i l i t y that a i r currents would cause intermingling of odour so that the atmosphere immediately above the logs would be a homogenous mixture. The role of fermenting bark odours is discussed more f u l l y i n a l a t e r section. It is the opinion of the writer that the insects under discussion a l i g h t on'slash i n a random manner regard-less of diameter and the associated features involved with diameter. Unless the requirements of the bark-beetle are s a t i s f i e d however, they continue t h e i r search. Blackman (1931) describes the searching movement of the Black H i l l s ^ beetle (Dendroctonus ponderosae)and the careful examination of the bark surface before commencement of boring into the 32 * 35 bark. The beetles do not necessarily e s t a b l i s h entry holes i n the immediate v i c i n i t y of the spot where they a l i g h t . Ips p i n i were observed to behave i n a s i m i l a r fashion on slash. There i s a decided tendency f o r Ips p i n i beetles to make entry holes under large hard bark f l a k e s . Thomas (1952) found that Ips p i n i preferred the rough thicker bark i n the regions near the butt end of white pine. On lodgepole pine, the hard f l a k y character of bark on the main stem provides greater support and hence the beetles have greater success i n estab-l i s h i n g entry holes. In summary therefore, the preference, shown by Ips p i n i for the larger slash diameters i s apparently due mainly to the thickness and roughness of the outer bark. 34 Frequency D i s t r i b u t i o n of Attacks within the Slash Neyman (1939) has stated the problem of f i t t i n g t h e o r e t i c a l d i s t r i b u t i o n s to empirical data i n these words: "Mathetmatics i s always dealing with the con-ceptional sphere, which i s d i s t i n c t from the per-ceptual and, at most, admits the p o s s i b i l i t y of est a b l i s h i n g some correspondence. Therefore, how-ever hard we tr y , we can never produce anything l i k e , a r e a l mathematical explanation of any phenom-enon but only some int e r p o l a t i o n formula, some system of conceptions and hypotheses, the conseque-nces of which are approximately s i m i l a r to the observable f a c t s . " Table II records the actual frequency of attacks or s t r i k e s per l i n e a l foot i n each block and compares this with the t h e o r e t i c a l values of three empirical frequency d i s t r i b u t i o n s . By frequency d i s t r i b u t i o n i s meant the number of times (0,1,2,3, 17) strikes occur on a single 1-foot section of slash. To eliminate v a r i a t i o n due to size of the slash, a single diameter class, 3.5 inch - 3.9 inch, was selected. The frequency d i s t r i b u t i o n s in each block r e t a i n t h e i r r e l a t i v e positions even though great differences occur i n the population abundance of Ips p i n i between various blocks. In a l l blocks the Foisson type d i s t r i b u t i o n gave very high Chi square values and low p r o b a b i l i t y values. It may be interpreted from this that the bark-beetles do not dis t r i b u t e themselves even within a single diameter class i n a com-( 35 p l e t e l y random fashion but rather appear to have a selective tendency. The negative binomial d i s t r i b u t i o n gave much lower Chi square values but s t i l l low p r o b a b i l i t i e s . The negative binomial assumes a continuous v a r i a t i o n , unlike Neyman's contagious and the Poisson d i s t r i b u t i o n s which are character-is e d by discontinuous v a r i a t i o n s . In a l l blocks, Neyman's contagious d i s t r i b u t i o n gave consistently greater conformity with the actual d i s t r i -bution. Block VI i n p a r t i c u l a r gave a f a i r l y high probab-i l i t y f i g u r e . The contagious aspect of this type of d i s t r i -' bution implies that where one insect was found, there i s a l i k e l i h o o d that some more w i l l be found. In the case of Ips p i n i , the presence of one bark-beetle indicates that a piece of slash has s a t i s f i e d the requirements and is suitable f o r the establishment of a g a l l e r y . It follows that the requirements f o r other bark-beetles w i l l be s i m i l a r l y sat-i s f i e d by that piece of slash or an adjacent piece with the same favorable features. I f a l l the slash i n the 3.5 to 3.9 inch diameter class had s a t i s f i e d the bark-beetle re-sponses, then i t is assumed the d i s t r i b u t i o n would have been random. But 'as the d i s t r i b u t i o n i s not random, there must be variations within the slash s u f f i c i e n t to repel or a t t r a c t the i n s e c t s . I 36 The variations which exist between slash of dif f e r e n t diameters was discussed i n the f i r s t section but differences also occur between pieces of slash i n the. same diameter class. The differences, while consisting of the same features - i . e . bark thickness, roughness, hardness are not so apparent i n slash of the same diameter class but are nevertheless of s u f f i c i e n t magnitude to be important i n the s u i t a b i l i t y of the slash f o r Ips p i n i attack. The chief difference noticed in slash of the same diameter class concerned differences i n surface character-i s t i c s of the bark. Slash from trees i n the intermediate and suppressed classes generally have the outer bark composed of small, c l o s e l y adhering f l a k e s , very hard and b r i t t l e . More rapid growing trees have s o f t e r bark, larger flakes which tend to c u r l around the periphery. Trees i n exposed locations generally have smoother bark with fewer scales due to more rapid sloughing-off by wind action and from the drying out~ effect of the run. Slash i n the same diameter class may not necessarily be from the same region on the trees. One piece of slash may be from higher on the stem of a f a s t growing tree while another piece, i n the same diameter class may be from lower on the stem of a slow growing tree. Figures 6, 7, 8, i l l u s t r a t e v a r i a t i o n i n the bark common i n the same diameter c l a s s . 37 Figure 6 I l l u s t r a t i n g bark surface from a lodgepole pine section i n the 3.5-3.9 inch dia-meter class. Note smoothness Figure 7 I l l u s t r a t i n g bark surface from a lodgepole pine section i n the 3.5-3.9 inch diameter cla s s . Note. large f l a t c l o s e l y ad-hereing bark scales Figure 8 I l l u s t r a t i n g bark surface from a lodgepole pine section i n the 3.5-3,9 inch diameter c l a s s . Note, abundance of large hard bark scales.with c u r l i n g edges 38 The effect of bark surface c h a r a c t e r i s t i c s and' the reaction of the bark-beetle to this feature was discussed e a r l i e r . The eff e c t on beetle dispersal within the same diameter class affected s i m i l a r l y . The temperature of the bark surface varies con-siderably, depending mainly on degree of exposure to solar radi a t i o n . Graham (1952) reports that logs having thin dark colored bark and exposed to direct sunlight may have temper-t ature of 60° F above the ambient a i r temperature, f a r above the l e t h a l point f o r bark-beetles. Bark temperatures i n shaded' locations tend to follow the a i r temperature. Beal (1933) found bark temperatures of 45° C to be f a t a l within several hours to the southern pine beetle (Dendroctonus f o n t a l i s Zimm.) Chamberlain (1939) presents a table ( a f t e r Graham) which gives the minimum l e t h a l temperature, average l e t h a l temperature, ai d maximum l e t h a l temperature of Ips p i n i adults as 111.2° F, 118.4° F, 122° F respectively. Surface bark temperatures of from 100° F to 120° F are not uncommon with a i r temper-o atures above 70 F. That bark-beetles are sensitive to these temperatures i s pointed out by Graham (1952) who mentions the fact that the upper sides of logs l y i n g i n the sun are usually free of bark-beetles. The most important'factors a f f e c t i n g the d i s t r i -bution of Ips p i n i adults within diameter classes would 3 9 therefore appear to be the outer bark c h a r a c t e r i s t i c s i n -cluding the degree of exposure to which each piece of slash is subjected. 40 Relationship Between Abundance of Bark-Beetles and Method of Gutting The area i n which this i n v e s t i g a t i o n was carried out formed a small part of a larger region notable f o r i t s great s i m i l a r i t y of forest cover. P r i o r to logging operations the area was uniform throughout i n respect to s i t e conditions, stems per acre, and growth, so i t may be assumed that the bark-beetle populations vi/ere s i m i l a r as regards species present and t h e i r abundance. By spring however the environ, ment i n each block had been changed by selective logging carried out the proceeding winter. The condition of the slash i n the spring was the same, but d i f f e r e n t volumes were con-tained i n each block. Table VII shows the l i n e a l feet of slash i n each block. The differences i n the mean number of strikes among the blocks was shown to be highly s i g n i f i c a n t (Table V). The differences i n means between i n d i v i d u a l t blocks I and IV, I and I I , VI, VIII, IV; and between IV and I ' l l , VI, VIII, were found to be s i g n i f i c a n t . No s i g n i f i c a n t differences occur among blocks I I , VI, VIII. Table VII shows the -mean number of strikes per foot long section of slash i n each block and indicates the extent to which the abundance of Ips p i n i varied between blocks. 41 TABLE VII Block I 7474.7 3.46 Total l i n e a l feet Mean No. strikes by bark-beetles per l i n -eal foot Total No. strikes 25862.4 by bark-beetles Block II 9284.1 1.65 15315.8 Block IV 2503 0.68 Block VI 9836.5 2.00 1702.6 19673 Block VIII 10268.1 2.12 21770.4 It appears that the most important single f a c t o r a f f e c t i n g absolute abundance of Ips p i n i within an area can be correlated with the volume of slash l a i d down. Block IV with only 2503 l i n e a l feet of slash, contained fewer Ips  p i n i adults than did Block VIII with 10,268 feet of slash. This does not mean that block IV was carrying i t s f u l l capa-c i t y of bark-beetles, f o r as shown i n Table i : , only 28$ of the available slash was attacked. The method by which bark-beetles are attracted to favorable hosts has long been attr i b u t e d to an odour response. Person (1931) i n i t i a t e d an i n v e s t i g a t i o n into this phenomenon i n his work on determining why the black h i l l s bark-beetle, when attacking yellow pine, showed a tree 42 se l e c t i o n behaviour. A vigorous tree produces a copious flow of oleoresins which normally prevent bark-beetles from be-coming established, while the flow i n subnormal trees i s con-siderably reduced. Person's explanation of the a b i l i t y of bark-beetles to recognize susceptible trees i s as follows:-" i n i t i a l a t t r a c t i o n of beetles to a tree i s due to formation and escape of v o l a t i l e aldehydes or esters which are by-products of a respiratory fermentation r e s u l t i n g from abnormal enzyme a c t i v i t y i n subnormal trees." He states further that the inner l i v i n g bark i s the most a t t r a c t i v e major part of the tree while fermenting bark is the most a t t r a c t i v e of the substances tested. Person refers to work by J e f f r e y who found that when a tree i s f e l l e d or severely injured there i s an increase i n levulose and a decrease i n sucrose, in d i c a t i n g a sucrose hydrolysis which would probably lead to accelerated fermentation. The greater the volume of slash i n an area, the more intensive w i l l be the odours i n the atmosphere from the fermenting bark and sapwood. The distance 'this odour per-meates throughout the surrounding stand i n s u f f i c i e n t con-centration to a t t r a c t bark-beetles i s not known.. Bark-beetles f l i g h t over great distances i s considered to be a passive process i n which they are transported by p r e v a i l i n g winds. Chamberlain (1939) quoting F e l t , refers to new infestations 43 of Scolytus mult i s t r i a t u s (which acts as a vector f o r the Dutch elm disease,) observed up to distances of 125 miles from the nearest center of i n f e s t a t i o n and these new infestations l a y in the d i r e c t i o n of the general p r e v a i l i n g winds. Blackmore (1931) describing t h e . f l i g h t of the Black H i l l s beetle ob-served dispersal over long distances i n a d i r e c t i o n corresp-onding with the pr e v a i l i n g wind. It i s u n l i k e l y that the Ips p i n i population est-tablished within the experimental area was the r e s u l t of mass "invasion" from distant sources but undoubtedly due to i n f i l -t r a t i o n from adjacent stands, possibly from distances up to 5 miles. The pre v a i l i n g wind is mainly from the north-west but wind d i r e c t i o n not infrequently changes f o r short periods during the day. I f the bark-beetles entered the area by transport of the pr e v a i l i n g wind then i t would be expected that the largest population would be i n those blocks located near the north-west corner of the experimental area. It would further be expected that the plots within these blocks would show a gradation i n abundance of Ips p i n i from north-west to south-east, larger populations occurring i n the north-west d i r e c t i o n . This i s not the case, however, as the block with the largest population is i n the south-west corner. An analy-sis of mean values f o r populations i n in d i v i d u a l plots also f a i l s to give any ind i c a t i o n that the population entered mainly from a north-west d i r e c t i o n . If the bark-beetles entered the area s o l e l y by orientation into wihd-borne odours, the high population i n block I would thus be explained, i . e . odours from the bark of fermenting slash would permeate'throughout the region l y i n g to the south-west of the experimental area and this would a t t r a c t bark-beetles from this region.. Moreover, i t would also be expected that blocks IV and II would be heavily attacked. This i s not so, however, as these two blocks have the lowest populations i n the entire area. Also, i t would be expected there would be a gradation from heavier to l i g h t e r numbers of attacks i n block I, i n a south-east to north-west d i r e c t i o n . Plot analyses f a i l to reveal this type of disper-s a l . However this should not be interpreted as i n d i c a t i n g a lack of orientation on the part of bark-beetles into wind-borne odours. The greater part of the population may have come i n from the south-west due to p r e v a i l i n g winds, but may be influenced also by winds of short duration from other d i r -ections. Bark-beetles could, and probably did, enter the area i n varying numbers from a l l direc t i o n s , some even by passive f l i g h t over short distances with the wind. Once they arrived within the logged area however, orientation became less a result of odour and more a response to other environmental fa c t o r s . Hierholzer (1951), studying f l i g h t behaviour and host selection of Ips curvidens believes both scent and sight are involved, scent being more important over short distances while sight i s the more important over longer distances. 45 Block I, as shown i n the tables, appears to possess some s i g n i f i c a n t l y a t t r a c t i v e property which resulted i n the establishment of a much higher population than occurred i n the other blocks. The environment within this block most c l o s e l y simulated the untouched stand condition. The block was heav-i l y thinned from below, but a l l dominant trees remained; the normal upper crown conditions were least disturbed. Within this' block i t i s expected therefore that temperature and humidities of the atmosphere and of the slash would remain more constant and least l i k e l y to undergo the extremes found in the other blocks. Close vis u a l observations supported this view. Therefore within block I, there exists the least modified natural stand meso-and micro-climate. As reported e a r l i e r by S.A.G-raham, bark temperatures tend to follow a i r temperatures i n shaded slash while i n exposed slash they may rise above the l e t h a l maximum during the day. Heavily logged areas would therefore present much warmer bark temperatures to the bark-beetles, this temperature often being so high as to repel the beetle. Furthermore, atmospheric humidity is lower, ;.bark dries out more r a p i d l y i n the exposed situations and the entire environment i s less favorable as compared with the natural untouched stand. Bark beetle movement i s f a i r l y free over the entire experimental area, being li m i t e d only by the fermentation odours a r i s i n g therein. The o r i g i n a l entering population i n block I remained and became established 46 Many bark-beetles o r i g i n a l l y c i r c u l a t i n g throughout the other blocks by t h e i r chance haphazard f l i g h t entered block I, and also established g a l l e r i e s within this block. The f i n a l r e s u l t , by the time the spring f l i g h t was over, was that blo,ck I attracted and retained the largest population. The large volume of data which was coll e c t e d i n this i n v e s t i g a t i o n made a c o m p l e t e a n a l y s i s i n one winter season impossible. It i s anticipated that the following points w i l l be determined at a l a t e r date* population of bark-beetles on the basis of a square foot of bark surfaces; mortality occurring i n each block during the summer and winter; r e l a t i o n -ship of altered meso-and micro-climates to mortality within each block, parasite and predator complex associated with bark-beetles, relationship of slash s u s c e p t i b i l i t y to bark c h a r a c t e r i s t i c s ; additional data on the biologies of other bark-beetles found i n f e s t i n g lodgepole pine slash. 47 SUMMARY AND CONCLUSIONS During the summer of 1952, an investigation was carried out to determine bark-beetle d i s t r i b u t i o n s and populations associated with s e l e c t i v e l y cut stands of lodge-pole pine and to evaluate and explain some of the major factors underlying the va r i a t i o n s . The area involved was located i n the F o o t - h i l l Section of the Boreal Forest Region approximately 20 miles south-west of Rocky Mountain House, Alberta. The l i f e cycle and habits of Ips p i n i Say. have been determined f o r the Rocky Mountain region and are described. This species was found to overwinter i n the duff at the base of infested trees and also under the bark of infes'ted trees. Overwintering insects are found i n the adult, l a r v a l and pupal stages under the bark. Adults, under favorable con-ditions w i l l e s t a b l i s h two broods and i t i s suspected the l i f e of mature adults does not exceed two consecutive summers. A d e f i n i t e r e l a t i o n s h i p was found to exist between diameter of the slash and s u s c e p t i b i l i t y to attack by bark-beetles . Reasons for this s e l e c t i o n are not known at present but the p o s s i b i l i t y of variation of bark c h a r a c t e r i s t i c s between diameter classes i s considered to be important. 48 The d i s t r i b u t i o n of the bark-beetles within a single slash diameter class i n each block was found to be similar and conformed most c l o s e l y with Neyman's contagious d i s t r i b u t i o n , i n d i c a t i n g a lack of randomness. The factors Responsible for this selective behaviour include one or a combination of: bark texture, exposure, temperature and humidity, odour. The blocks, each cut under a d i f f e r e n t selective method, attracted varying numbers of bark-beetles into the area. The quantity of slash was the important i n i t i a l attractant, but when slash volumes were approximately equal, other factors became dominant. The area most c l o s e l y simulating natural conditions of the untouched stand attracted the largest population and the possible reasons f o r this are enlarged upon i n the discussion. 49 LITERATURE CITED Beal, J.A. "Temperature Extremes as a Factor i n the 1933 Ecology of the Southern Pine Beetle." Jour, f o r - Vol. 31, (3), March 1933. Beal, J.A. "Relation of A i r and Bark Temperature of 1934 Infested Ponderosa Pine during Subzero Weather" Journal Econ. Ent. Vol. 27, 6, December 1934. Beal, J^A., C.L. Massey, Bark-Beetles and Ambrosia 1945 Beetles (Coieoptera; Scolytoidea); B u l l e t i n #10 Duke Unive r s i t y School of Forestry, Durham, N.C. Blackman, M.W. "The ^Black H i l l s Beetle" (Dendroctonus 1951 ponderosae Hopk) Tech. Pub. 36, New York State College of Forestry, Syracuse University, Syracuse, N.y. Chamberlain, W.J. "The Bark & Timber Beetles of North 1939 America" Oregon State College Co-operative Assn. Corvalis, Oregon. Clemens, W.A., "The Pine Bark Beetle," B u l l e t i n 585, 1916 Cornell University A g r i c u l t u r a l Experimental Station, I t h i c a , New York. Dodge, H.R. "The Bark Beetles of Minnesota," 1938 (Coieoptera: Scolytidae) Technical B u l l e t i n 132, U n i v e r s i t y of Minnesota A g r i c u l t u r a l Experimental Station Graham, S.A.,Forest Entomology, 1952 McGraw-Hill Book Co. New York, Toronto Halliday, W.E.D., "A Forest C l a s s i f i c a t i o n of Canada." 1937 Forest Service B u l l e t i n 89, Dominion ' Department of Mines and Resources, Ottawa, Canada'. Hierholzer, 0. "Die Bedeutung der Sinnesphysiologie i n der 1951 Schadlingsbekampfung-erklart an Untersuehungen uber die Orientierung des grossen Krummzahnigen Tannenborkenkafers, Ips curvidens Germ." r e f . i n For. Abstracts, 13 (1): 75 entry 498 September 1951 i 50 Hopping, G.R. G. B e a l l , The r e l a t i o n of diameter of Lodgpole 1948 Keen, F.P. 1936 Ne.yman, J . 1939 Person, 1931 H »L • Snedecor, G.W. 1937 Swaine, 1918 J.l Thomas, J.B, 1952 Tragardh, I, 1930 Tragardh, 1938 Wadley, F.M., 1950 pine to incidence of attack by the bark-beetle, Dendroctonus monticolae Hopk. For. Chron, 24 (2) "Relative S u s c e p t i b i l i t y of ponderosa pines to bark-beetle attack". Journal Forestry 54: 919-927, October. "Contagious D i s t r i b u t i o n s , " Ann. Math. Stat. 10:35 - 57. "Theory i n explanation of the Selection of Certain Trees by the Western Pine Beetle" Journal Forestry 29, 696-699, 1931 S t a t i s t i c a l Methods, Collegiate Press, Ames, Iowa. "Canadian Bark-Bee t i e s , " B u l l e t i n 14, Part I I , Dominion Department of A g r i c u l t u r e . "Bark-beetle Development and Associated Insects i n White and Red Pine Logging Slash" Unpublished Thesis f o r M.Sc. McGill Univer-s i t y , May, 1952. ' • "Studies on the Galleries of the Bark-beetie" Reprinted from B u l l , of Ent. Research, Vol. XXI Pt. 4, December 1930. V. Butovitach, "Some Forest Entomological Methods and Conceptions". Entomological Department, Royal Swedish Insti t u t e of Experimental Forestry, Experi-mentalfaltet, Sweden) Reprinted from the B u l l . Ent. Res. Vol. 29, Pt. 2, July 1938. Notes on the form of D i s t r i b u t i o n of Insect and Plant Populations, Ann. Ent. Soc. Amer. 43:581 - 86 APPENDIX iP ILLUSTRATING DESIGN OF EXPERIMENT BLOCK I - Heavily thinned from below reducing the number of commercial stems from 664 to 300 per acre. Dominant trees remain. II - Heavily thinned from above reducing the number of commercial stems from 698 to 300 per acre. Sub-dominant and suppressed trees remain. I l l - Sanitation cut - a l l dying, deformed, suppressed trees removed. IV - Merchantable trees cut to a diameter l i m i t of 6.5 inches, reducing the number of stems from 697 to 521. V - Uncut control. VI - A l l merchantable volume removed except 10 seed trees per acre. VII - Clear cut. VIII - Shelterwood cutting, 70 crop trees per acre removed. IX - Patch logging, c i r c u l a r areas, 50 foot diameter clear cut. Plot centers are indicated i n each block and i d a n t i f l e d as i n Block 5 on Map. BLOCK 9 • • • • • • • • • BLOCK 6 • • • • • • • • • BLOCK 3 • • • • • • • • • BLOCK 8 • • • • t • • • • BLOCK 5 * A • B Z- -Y W- -X •E •F BLOCK 2 • • • • • • • • • BLOCK 7 • • • • • • • • • BLOCK 4 • • • • • • • • • BLOCK I • • • • • • • • • 

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