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Ecological studies of Hylobius radicis Buch., H. Pales (HBST.) and Pissodes approximatus Hopk. (Coleoptera:… Finnegan, Raymond Rene Joseph 1958

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©lie Pmtarsti|j of r^tttsij (Eolomdbia Faculty of Graduate Studies PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY "t RAYMOND JOSEPH FINNEGAN B.Sc.F. New Brunswick 1948 M.Sc.F. New Brunswick 1950 IN ROOM 187A BIOLOGICAL SCIENCES BUILDING Saturday, November 8, 1958 9:30 a.m. COMMITTEE IN CHARGE DR. F. H. SOWARD, Chairman K. GRAHAM G. S. A L L E N I. McT. COWAN J. E. BIER P. A. LARKIN V. KRAJINA DEAN W. H. G A G E External Examiners of Thesis JOHN MacSWAIN (Univ. of California) JULIUS A. RUDINSKY (Oregon State College) W. G. WELLINGTON (Division of Forest Biology) ECOLOGICAL STUDIES OF HYLOBIUS RAD1C1S BUCH., H. PALES (HBST.) AND PISSODES APPROXIMATUS HOPK. (COLEOPTERA: CURCULIONIDAE) IN SOUTHERN ONTARIO. ABSTRACT Three native weevils have become increasingly important in recent years in stands of planted pines in southern Ontario. The pine root collar weevil, Hyldbius radicis finch., breeds in the root collar of healthy pines, killing over 90% of the trees in some plantations. The pales weevil, H. pales (Hbst.), and the northern pine weevil, Pissodes approximates Hopk., are important because the adults, feeding on the tender bark of twigs and small branches of healthy pines, kill the branches or even the whole tree. The life histories and bionomics of the three species were determined from natural populations in the field and colonies in the insectary. These studies were facilitated by a special technique devised for rearing the weevils permitting continuous observation's of larval and pupal development and periodic measurement of body size and larval feeding. Stand density is the chief factor regulating populations: of H. radicis, fostering high populations in the dense stands of plantations, and excluding the insect from sparser natural stands. Scots pine is evidently more susceptible than red pine to H. radicis where the two tree species grow together, but the presence of Scots pine increases the infestation in red pine. Availability of suitable breeding material in the form of numerous stumps left after cutting is the factor governing the number of H. pales and P. approximates. The implications for forestry consist of recom-mendations to avoid pure dense stands especially of exotic species, and to practice forest sanitation in cutting operations. PUBLICATIONS STEWART, K. E., R. J. FINNEGAN AND C. S. KIRBY. Control of Fletcher scale, Lecanium fletcheri Ckll., on Japanese yew. Can. Dept. Agr., For. Biol. Div., Bi-Monthly Prog. Rept. 9 (2): 3. 1953. FINNEGAN, R. J. Weevils attacking pines in southern Ontario. Can. Dept. Agr., For. Biol. Div., Bi-Monthly Prog. Rept. 12(2): 3. 1956. FINNEGAN, R. J. Elm bark beetles in southern Ontario. Canad. Ent. 89 (6): 275-280. 1957. FINNEGAN, R. J. The pine weevil, Pissodes approximates Hopk., in southern Ontario. Canad. Ent. 90(6): 384-354. 1958. Faculty of Graduate Studies PROGRAMME OF THE FINAL ORAL EXAMINATION FOR THE DEGREE OF DOCTOR OF PHILOSOPHY RAYMOND JOSEPH FINNEGAN B.Sc.F. New Brunswick 1948 M.Sc.F. New Brunswick 1950 IN ROOM 187A BIOtOGICAL SCIENCES BUILDING Saturday, November 8, 1958 9:30 a.m. COMMITTEE IN CHARGE DR. F. H. SOWARD, Chairman K. GRAHAM G. S. A L L E N I. McT. COWAN J. E. BIER P. A. LARKIN V. KRAJINA DEAN W. H. G A G E External Examiners of Thesis JOHN MacSWAIN (Univ. of California) JULIUS A. RUDINSKY (Oregon State College) W. G. WELLINGTON (Division of Forest Biology) ECOLOGICAL STUDIES OF HYLOBWS RADICIS BUCH., H. PALES (HBST.) AND PISSODES APPROXIMATUS HOPK. (COLEOPTERA: CURCULIONIDAE) IN SOUTHERN ONTARIO. ABSTRACT Three native weevils have become increasingly important in recent years in stands of planted pines in southern Ontario. The pine root collar weevil, Hylobius radicis Buch., breeds in the root collar of healthy pines, killing over 90% of the trees in some plantations. The pales weevil, H. pales (Hbst.), and the northern pine weevil, Pissodes approximatus Hopk., are important because the adults, feeding on the tender bark of twigs and small branches of healthy pines, kill the branches or even- the whole tree. The life histories and bionomics of the three species were determined from natural populations in the field and colonies in the insectary. These studies were facilitated by a special technique devised for rearing the weevils permitting continuous observations of larval and pupal development and periodic measurement of body size and larval feeding. • Stand density is the chief factor regulating;.;populations; of H. radicis, fostering high populations in the dense stands of plantations, and excluding the insect, from sparser natural stands. Scots pine is evidently more susceptible than red pine to H. radicis where the two tree rspecies* grow together,. but the presence of Scots pine increases the infestation in red pine. Availability of suitable breeding material in the form of numerous stumps left after cutting is the factor governing the number of H. pales and P. approximatus. The implications for forestry consist of recom-mendations to avoid pure dense stands especially of exotic species, and to practice forest sanitation in cutting operations. PUBLICATIONS STEWART, K. E., R. J. FINNEGAN AND C. S. KIRBY. Control of Fletcher scale, Lecanium fletcheri Ckll., on Japanese yew. Can. Dept. Agr., For. Biol. Div., Bi-Monthly Prog. Rept. 9 (2): 3. 1953. FINNEGAN. R. J. Weevils attacking pines in southern Ontario. Can. Dept. Agr., For. Biol. Div., Bi-Monthly Prog. Rept. 12(2): 3. 1956. FINNEGAN, R. J. " Elm bark beetles in southern Ontario. Canad. Ent. 89 (6): . 275-280. 1957. FINNEGAN, R. J. The pine weevil, Pissodes approximates Hopk., in' southern Ontario. Canad. Ent. 90(6): 384-354. 1958. ECOLOGICAL STUDIES OF HYLOBIUS RADICIS BUCH., H. PALES (HBgT.) AND PISSODES APPROXIMATUS HOPK. (COLEOPTERA : CURCULIONIDAE) IN SOUTHERN ONTARIO. lay RAYMOND JOSEPH FINNEGAN B. Sc. (F.) 1948, U n i v e r s i t y of New Brunswick. M. Sc. (P.) 1950, U n i v e r s i t y of New Brunswick. A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Zoology We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September, 1958. ABSTRACT Three native weevils have "become i n c r e a s i n g l y important i n recent years i n stands of planted pines i n southern Ont-a r i o . The pine root c o l l a r weevil, Hylobius r a d i c i s Buch., breeds i n the root c o l l a r of healthy pines;, k i l l i n g over SO<fo of the trees i n some p l a n t a t i o n s . The pales weevil, H. pales. (Host.), and the northern pine weevil, Pissodes  a-p-proximatus Hook.» are important because the adults, feeding on the tender bark of twigs and small branches of healthy p i n e s t k i l l the branches or even the whole t r e e . The l i f e h i s t o r i e s and bionomics of the three species were determined from natural populations i n the f i e l d and colonies i n the i n s e c t a r y . These studies were f a c i l i t a t e d by a s p e c i a l technique devised f o r r e a r i n g the weevils permitting continuous observations of l a r v a l and pupal development and p e r i o d i c measurment of body s i z e and l a r v a l feeding. Stand density i s the c h i e f f a c t o r r e g u l a t i n g popula-t i o n s of H. r a d i c i s , f o s t e r i n g high populations i n the dense stands of plantations, and excluding the insect from sparser natural stands. Scots pine i s evidently more susceptible than red pine to H. r a d i c i s where the two tree species grow together, but the presence of Scots pine increases the i n f e s -i i i t a t i o n i n red pine. A v a i l a b i l i t y of s u i t a b l e breeding m a t e r i a l i n the form of numerous stumps l e f t a f t e r c u t t i n g i s the f a c t o r governing the number of H. pales and P. approximatus. The implications f o r f o r e s t r y consist of recommendations to avoid pure dense stands e s p e c i a l l y of exotic species, and to p r a c t i c e f o r e s t s a n i t a t i o n i n c u t t i n g operations. In presenting t h i s thesis i n p a r t i a l 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 s h a l l make i t f r e e l y available for reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by his representative. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. The University of B r i t i s h Columbia Vancouver 8, Canada. Department of i v CONTENTS Page INTRODUCTION 1 TAXONOMY 4 METHODS 10 Study of Insect B i o l o g i e s 10 Measurment of Damage 15 HYLOBIUS RADICIS BUCK 19 H i s t o r y 19 D e s c r i p t i o n of L i f e H i s t o r y Stages 21 D i s t r i b u t i o n and Hosts 29 Seasonal History 50 Habits • 34 L i m i t i n g Factors 42 E f f e c t on the Tree 46 HYLOBJJJS PALES (HBST.) 56 History 57 D e s c r i p t i o n of L i f e H i s t o r y Stages 59 D i s t r i b u t i o n and Hosts 64 Seasonal History 67 Habits 71 L i m i t i n g Factors 74 E f f e c t on the Tree 77 V PISSODES APPROXIMATUS HOPE 78 H i s t o r y . .. 78 D e s c r i p t i o n of L i f e H i s t o ry Stages t . 1... 79 D i s t r i b u t i o n and Hosts 83 Seasonal History 84 Habits t- i. 85 L i m i t i n g Factors *... i ... 91 E f f e c t on the Tree' 94 DISCUSSION AND ^ CONCLUSIONS .. ..; : 95 BIBLIOGRAPHY 103 FIGURES F i g . 1. Method,;.of r e a r i n g pine weevils i n the insec t a r y from the egg to the adult stage showing, (a) pouring the sa'nd over the * inner bark and screen; (b) a s e c t i o n a l view of the rea'ring u n i t 12 F i g . 2. Larvae of Hylobius r a d i c i s i n rear i n g (a) Feeding l a r v a , (b) Prepupa i n pupal - r c e l l 14 F i g . 3. Caged pine trees used i n studying the bionomics of Hylobius r a d i c i s 17 F i g . 4. Hylobius r a d i c i s . (a) Egg x24; (b) Larva x6; (c) Pupa i n earthen c e l l x6; (d) Adult x6 22 F i g . 5. Dorsal view of (a) Hylobius r a d i c i s and (b) H. pales, showing the* scattered spots'' on the e l y t r a of H. r a d i c i s i n contrast to the barred p a t t e r n on the e l y t r a of H. pales .. ..... 23 v i P i g . 6. (a) Hind t i b i a l uncus of Hylobius r a d i c i s males; (b) Hind t i b i a l uncus of H. -pales males; (c) Hind t i b i a l uncus °f H» r a d i c i s and H. pales females and (d) Abdominal impressions found on H. r a d i c i s and H. pales males. .. . 26 P i g . 7. D i s t r i b u t i o n of head capsule measurments of 84 Hylobius r a d i c i s larvae reared i n the insectary from the egg to the adult.. The cross-hatched areas represent the overlap between adjacent i n s t a r s 27 Pi g . 8. D i s t r i b u t i o n of head capsule measurments of Hylobius r a d i c i s , representing (a) 476 larvae c o l l e c t e d i n Jthe f i e l d V (b) 84 ' " larvae reared i n the ins e c t a r y . ......... 28 Pi g . 9. Seasonal h i s t o r y of Hylobius r a d i c i s i n southern Ontario. ... 31 Pi g . 10. Section through the root c o l l a r of a s i x - i n c h Scots pine showing t y p i c a l wounds caused by Hylobius r a d i c i s l a r v a e . This tree had been in f e s t e d f o r at l e a s t t h i r t e e n ye%rs. 35 p i g . 11. Hylobius r a d i c i s damage to. the root c o l l a r of Scots pine, (a) Root c o l l a r of i n f e s t e d tree with the p i t c h - i n f i l -t r a t e d s o i l p a r t l y removed to show a l a r v a i n the outer bark; (b)stump of in f e s t e d tree with s o i l completely removed to show swelling at the root c o l l a r due to l a r v a l damage; (c) Stump of i n f e s t e d tree wi'th bark removed from the root c o l l a r to show extent of damage to the wood. 36 Pi g . 12. D i s t r i b u t i o n of Hylobius r a d i c i s larvae and pupae i n the s o i l around the root c o l l a r of i n f e s t e d Scots pines i . . . . 39 p i g . 13. Emergence of Hylobius r a d i c i s adults from twenty trees during the summer of 1955 40 v i i P i g . 14. Hylobius r a d i c i s damage, (a) A hea v i l y i n f e s t e d twenty-year-old Scots pine pl a n t a t i o n ; (b) Two i n f e s t e d trees broken at the root c o l l a r and blown over by wind. .48 P i g . 15. Growth curves of 20 red pines and 20 Scots pines, h e a v i l y i n f e s t e d with .-•- Hylobius r a d i c i s , and 10 healthy white pines growing i n a mixed stand. The trees were a l l 22 years old 51 P i g . 16. Hylobius r a d i c i s damage, showing a l i e r -nate rows of l i v i n g i n f e s t e d red pines •• and dead Scots pines 54 P i g . 17. Hylobius pales adult xlO 60 P i g . 18. D i s t r i b u t i o n of head capsule measurments of 75 Hylobius pales larvae reared i n the insectary from the egg to the adul t . The black area represents the measurments of the f i f t h i n s t a r larvae that continued development to a s i x t h i n s t a r before pupat-i n g . 62 P i g . 19. Relationship between the head capsule s i z e of prepupae and adults of Hylobius  pales. The regression l i n e Y = 0.413X + 0.889 has been f i t t e d to the data. 65 P i g . 20. Seasonal h i s t o r y of Hylobius pales i n southern Ontario * 68 P i g . 21. Pissodes apprdximatus • adult x l 2 . 80 P i g . 22. D i s t r i b u t i o n of head capsule measurments of Pissodes approximatus larvae.. .......... 81 P i g . 23. Seasonal h i s t o r y of pissodes approxi-matus in., southern Ontario. 84 P i g . 24. Larva of Pissodes approximatus i n re a r i n g . Note l a r v a l mines parallel'' to the g r a i n of the bark V... 88 P i g . 25. "Chip cocoons M of Pissodes approximatus showing, (a) one c e l l i n t a c t and (b) another opened to reveal the prepupa i n -s i d e . Note the e x c e l s i o r - l i k e covering v i i i , of the c e l l s 90 F i g . 26. Stem of a three-inch red pine i n f e s t e d with pissodes approximatus (pupal stage). 92 F i g . 27. Four-inch Scots pine stump i n f e s t e d with Pissodes approximatus and Hylobius  pales (pupal stage). The lack of pupal c e l l s above ground l e v e l i s due to com-p e t i t i o n from bark beetles. 93 TABLES TABLE I The duration of the immature stages of Hylobius r a d i c i s reared i n an un-heated insectary during the summer-season. 33 TABLE II M o r t a l i t y of immature Hylobius r a d i c i s c alculated from populations on 60 red pines and 78 Scots pines and expressed as a percent of the i n i t i a l egg popula-t i o n . 46 TABLE III Growth r a t i o s f o r 20 Scots pines and 20 red pines h e a v i l y i n f e s t e d with Hylo- bius r a d i c i s 52 TABLE IV Comparison between observed head capsule widths of Hylobius pales larvae and those estimated by using Dyar's Rule 63 TABLE V The duration of the immature stages of Hylobius pales reared i n an unheated i n -sectary during the summer season 70 TABLE VI Comparison between observed head capsule* widths of Pissodes approximatus larvae by using Dyar's Rule and on the basis of a l i n e a r regression r e l a t i o n s h i p . 82 TABLE VII The duration of the immature stages - of pissodes approximatus reared i n an un-heated insectary during the summer months. 86 ACKNOWLEDGEMENT S I wish to express my indebtedness to Dr. K. Graham, Professor of Porest Entomology, and Dr. I. McTaggart Cowan, Head of the Department of zoology, U n i v e r s i t y of B r i t i s h Columbia, f o r t h e i r guidance, encouragement and advice during t h i s study. Much of the f i e l d work was made p o s s i b l e only by the frequent assistance and guidance of Dr. R. M. Belyea, Officer-in-Charge, Porest Insect Laboratory, Sault Ste. Marie, Ont. Permission to use data obtained while i n the employ of the Federal Government was granted by Dr. M. L. Prebble, Chief, Porest Biology D i v i s i o n . I wish to thank Drs. R. M. Belyea and M. L. Prebble f o r t h e i r c r i t i c i s m s of the manuscript. The photographic work was done by Mr. D. C. Anderson, B i o -photographer, Porest Insect Laboratory, Sault Ste. Marie, Ont. ECOLOGICAL STUDIES OP HYLOBIUS RADICIS BUCH., S. PALES (HBST.) AND PISSODES APPROXIMATUS HOPE. (COLEOPTERA t CURCULIONIDAE) IN .SOUTHERN ONTARIO. INTRODUCTION In recent years, weevil damage to pine trees grown i n county f o r e s t s and i n Christmas tree p l a n t a t i o n s has increased remarkably i n southern Ontario as well as i n the eastern United States. Several species of weevils are i n -volved, sometimes attacking i n d i v i d u a l l y , but mostly i n as s o c i a t i o n with one another. The complex includes the pine root c o l l a r weevil, Hylobius r a d i c i s Buch., the pales weevil, H. pales (Hbst.), the white pine weevil, Pissodes s t r o b i (Peck), the northern pine weevil, P. approximatus Hopk., and the strawberry root weevil, Brachyrhinus ovatus ( L e e ) . Although the importance of P. s t r o b i as a fo r e s t pest has been known f o r over a century i n North America, that of the other weevils i n the complex has not been f u l l y appreciated u n t i l more re c e n t l y . Two of them i n f a c t , have only been described as species since the turn of the century (P. app-roximatus and H. r a d i c i s ) • I t was the sudden r i s e from an unknown existence to economic importance of H. r a d i c i s i n southern Ontario i n 2 1.954 that l e d to the present i n v e s t i g a t i o n . A. b r i e f app-r a i s a l of the i n f e s t a t i o n i n Simooe County e a r l y i n 1955 showed that not only had H. r a d i o i s reached epidemic pro-portions i n the area, but that two other weevils of the complex (H. pales and P. approximatus) were also present i n s u f f i c i e n t numbers to contribute appreciably to the t o t a l damage of pine stands. The purpose of t h i s i n v e s t i g a t i o n has been to extend the present knowledge of the i n t e r r e l a t i o n s h i p s between the three weevils and t h e i r host p l a n t s ; of t h e i r economic importance; and of the e f f e c t of the environment on t h e i r reproductive p o t e n t i a l . H. pales and P. approximatus both breed i n dead or decadent pines and cause l i t t l e or no damage as l a r v a e . The adults, however, feed on the tender bark of coniferous seed-l i n g s and may cause serious damage where outbreaks occur. H. r a d i c i s , on the other hand, causes only s l i g h t damage by i t s adult feeding. However, i t s habit of attacking and breeding i n the root c o l l a r of healthy pines, often causing the death of the tree, makes t h i s weevil one of the more serious f o r e s t pests i n eastern North America. Although the three weevils are native to North America, i t i s only during the l a s t f i f t y years that they have been considered as important f o r e s t pests. This change of t h e i r 5 economic importance, as a d i r e c t r e s u l t of increase i n nunri' bers, has been due l a r g e l y to the actions of man by making a v a i l a b l e large q u a n t i t i e s of breeding m a t e r i a l e i t h e r by c l e a r c u t t i n g or by p l a n t i n g pure stands of pines. TAXONOMY The genus Hylobius belongs to the t r i b e H y l o b i i n i , sub-family Curculioninae, family Curculionidae. I t contains about 50 species, f i v e of which are native to North America; H. -pales (Hbst.)„ H. congener (Delia Torre) (-confusus Kby.), H. p i n i c o l a (Couper), H. r a d i c i s Buch,, and H. warreni Wood. Although these f i v e species are r e a d i l y separated i n t o two groups, the i n d i v i d u a l s within each group are very s i m i l a r and may be e a s i l y confused. H. pales, H. congener^and H. r a -d i c i s ^ on the average, are smaller than H. p i n i c o l a and H. warreni> and d i f f e r i n general appearance from them. The shape of the femora and the presence or absence of teeth on i t , as i s indi c a t e d i n the following key, are also important d i s t i n g u i s h i n g characters of the two groups. In 1934 Buchanan (16) described H. r a d i c i s as a new species and presented a synoptic key f o r H. pales, H. con- gener, and the new species H. r a d i c i s . These three weevils constituted a l l the North American species of the genus Hylobius known at that time. Recently, Wood (125) i n a r e -view of the North American a l l i e s of the Eurasian species Hylobius piceus (DeGeer), eliminated the genus Hypomolyx of Leconte by separating the single h o l a r c t i c species i n the genus, Hypomolyx piceus (DeGeer), into two separate species and transferring them to the genus Hylobius under the names H. piceus (palaearctic) and H. pinicola (nearctic). In the same paper he described a new North American species, H. warreni, which i s apparently closely related to H. pinicola. He also presented a key separating the three species involved, i . e . H. -piceus, H. pinicola, and H. warreni. In view of the excellent work done on these weevils by Leeonte (75), Buchanan (16) and Wood (125), the author pre-fers to present the following key synthesized from the work of the above taxonomists rather than attempt the construction of an independent key: , , Key to Species of North American Hylobius I. Femora club-shaped, strongly toothed 2 Femora feebly club-shaped, not toothed 4 2. Scutellum v i r t u a l l y glabrous; anterior face of at least the hind femur almost always with a narrow, shallow, median groove i n about basal third; inner edge of fore t i b i a of male with a fringe of white hair, the length of some of the longer hairs equal to width of t i b i a . Length 5,8 to 9.0 mm. congener (Delia Torre) Scutellum normally covered by a dense coating 6 of seta-like scales; hind femur rarely with even a trace of a groove; male without t ib ia l fringe as above 3 3 . Size smaller, 5 .8 to 11 .3 mm.; head normally with a spot or line of coarser seta-like scales on vertex or on front; punctures immediately behind inter-ocular puncture more or less strongly coalescent to form short, irregular rugae; hind t i b i a l uncus of male broad, parallel-sided, very broadly rounded at apex pales (Hbst.) Size larger, 9 .4 to 1 3 . 0 mm.; head without a line or spot of scales on front :<3f vertex; punctures behind interocular puncture generally separated by narrow intervals, or at most only feebly coalescent; hind t i b i a l uncus of male narrow, sides generally convergent to the sub-acute apex radicis Buch. 4. Rostrum rather stout, less than 2.6 times as long as wide, noticeably wider dist-al ly; apical umbones of the elytra obscure or entirely undefined; meta-7 •thoracic wings short, not extending "beyond the p o s t e r i o r margin of f i r s t v i s i b l e abdominal sternum; male geni-t a l i a with apex of aedeagus blunt, the anterodorsal margin of gonocoxites conspicuously bisinuate, and l a c k i n g a darkly pigmented median area w i t h i n the aedeagus warreni Wood Rostrum slender, more than 2.9 times as long as wide, not wider d i s t a l l y ; a p i c a l urn-bones of e l y t r a prominent; metathoracic wings long extending well beyond e l y t r a l apex; male g e n i t a l i a with apex of aedeagus acutely pointed, the anterodorsal margin of the gonocoxites evenly rounded; and a pigmented median t r i a n g u l a r or Y-shaped area within the aedeagus v i s i b l e from the v e n t r a l aspects p i n i c o l a (Couper) The genus Pissodes belongs to the t r i b e p i s s o d i n i , sub-family Curculioninae, family Curculionidae. I t i s a large and cosmopolitan genus with about 30 species i n North America alone (71). Several of the eastern North American species are so s i m i l a r morphologically, that i t has been found impossible to separate them on t h i s b a s i s . Since the s i m i l a r i t y between the species often extend to t h e i r b i o -nomics as w e l l , i t i s suggestive that perhaps the group i s experiencing an active period of evolution and that several populations p o s s i b l y e x i s t , at the sub - s p e c i f i c l e v e l . From personal communications with Dr. G. K. Manna 1 2 and Dr. S. G. Smith i t has been learned that a close i n t e r -r e l a t i o n s h i p e x i s t s among weevils of the genus Pissodes. Manna has found that P. s t r o b i (peek), P. engelmanni Hopk., and P. s i t c h e n s i s Hopk. a l l possess 34 chromosomes, while p. a f f i n i s Rand., P. radiatae Hopk., and P. f a s c i a t u s Rand, a l l possess 30 chromosomes. P. approximatus Hopk. and p. canadensis Hopk. on the other hand, possess from 30 to 34 chromosomes, there being a more or l e s s gradual change from 30 chromosomes i n weevils c o l l e c t e d i n southern Ontario to 32 chromosomes i n weevils c o l l e c t e d along the north shore of the Great Lakes, to 34 chromosomes i n weevils c o l l e c t e d i n c e n t r a l Manitoba. 'Science Service Postdoctorate Fellowship Holder, Forest Insect Laboratory, Sault Ste. Marie, Ont. Head* Section of Cytology and Genetics, Forest Insect Laboratory, Sault Ste. Marie, Ont. 9 Marina i s of the opinion that there i s no ground f o r separating t h i s population i n t o two species (P. approximatus i n the south and P. canadensis i n the north) as done by Hopkins (71). I t has been learned at a l a t e date that Manna and Smith have recently published t h e i r f i n d i n g s as discussed above. vide: MANNA, G. K. AND S. G. SMITH. 1958. Adaptive chromo-somal polymorphism and inter-relationships,, among bark weevils of the genus -Pissodes Germar. Proc. Inter. Congr. Genetics, p.178. METHODS The i n v e s t i g a t i o n s of H. r a d i c i s , H. pales, and P. approximatus were c a r r i e d out i n Simcoe County i n southern Ontario, during the 1955, 1956, and 1957 growing seasons. F i e l d observations were made i n several widely separated plantations of mixed eastern white pine, pinus strobus L., red pine, P. resinosa Ait.,, jack pine, P. banksiana Lamb., and Scots pine, P. s y l v e s t r i s L., and i n nursery s e e d l i n g beds at Angus and Midhurst, Ont. The laboratory observations were conducted at a f i e l d s t a t i o n at Angus, Ont. i n the summer, and at the U n i v e r s i t y of B r i t i s h Columbia and the Porest Insect Laboratory at Sault Ste. Marie, Ont. during the winter. Study of Insect B i o l o g i e s t In i n v e s t i g a t i n g the seasonal h i s t o r y and habits of the weevil complex, insect populations were kept under observation both i n natural breeding m a t e r i a l i n the f i e l d and i n cages i n the i n s e c t a r y . The weevils reared i n the insec t a r y consisted of the progeny of twelve p a i r s (male and female) of young H. r a d i c i s ; twelve p a i r s of young H. pales.; and twelve p a i r s of young p. approximatus. Each p a i r was kept separately i n glass v i a l s and permitted to feed and o v i p o s i t f o r two growing seasons on sections of pine 11 branches (four inches long and ^ inch i n diameter), placed i n the v i a l s . Since the females sometimes dropped t h e i r eggs away from the pine m a t e r i a l , the glass v i a l s were placed with t h e i r open ends down on a wire screen so that the loose eggs f e l l through the screen onto a watch glass placed under-neath. Fresh pine branches were added to the v i a l s d a i l y , while the branches of the previous day were c a r e f u l l y peeled and examined f o r eggs. The twelve H. r a d i c i s females l a i d 380 eggs during the two summers, but only 84 were reared to the adult stage. The H. pales females l a i d 556 eggs, of which 73 were reared to adults, and the twelve P approximatus females, l a i d 522 eggs, of which 42 were reared to a d u l t s . A s p e c i a l technique was devised f o r r e a r i n g the weevils. This consisted of r e a r i n g the i n s e c t from the egg to the adult stage under glass, on f r e s h inner bark of Scots pine removed from the t r e e . The newly hatched l a r v a was placed i n a. small groove made on the cambial surface of the bark which was then pressed t i g h t l y against the bottom of a p e t r i d i s h by f i l l i n g the di s h with sand and applying pressure on the cover with rubber bands (Pi g . 1 ) . The cover of the p e t r i d i s h was l i n e d with a "Kleenex" t i s s u e so as to prevent the sand from escaping between the two dishes and to maintain a more uniform pressure on the sand. The bark was prevented from drying out by s q u i r t i n g about 1 cc. of water each day 12 F i g . 1. Method of rearing pine weevils i n the insectary from the egg to the adult stage showing, (a) pouring the sand over the inner bark and screen; (b) a s e c t i o n a l view of the re a r i n g u n i t . 13 between the edges of the p e t r i dishes onto the "Kleenex" t i s s u e . During the prepupal stage, the larvae had a tendency to bore through the bark and disappear i n t o the sand. In order to prevent t h i s , a c i r c u l a r piece of galvanized wire screen wags cut to f i t snugly i n s i d e the p e t r i d i s h and placed over the bark before the sand was added. The screen d i s c , although preventing the prepupa from, entering the sand, d i d not i n t e r f e r e with the uniform pressure of the sand on the bark. This r e a r i n g method permitted continuous observations of l a r v a l and pupal development and the p e r i o d i c measurment of body s i z e and extent of l a r v a l feeding ( P i g . 2). I t was p o s s i b l e to keep the inner bark green and free from fungus contamination f o r more than two weeks by using s t e r i l i z e d sand and glassware, and by keeping to a minimum the time that the cambial surface of the inner bark was exposed to the a i r during preparations. In r e a r i n g the weevils some larvae were t r a n s f e r r e d to f r e s h bark a f t e r each moult, while others were t r a n s f e r r e d a f t e r two moults, thus per-m i t t i n g more accurate measurments of the feeding damage by each i n s t a r . A f t e r the l a s t i n s t a r larvae had constructed pupal chambers, they were l e f t undisturbed u n t i l the adults were formed. P i g . 2. Larvae of Hylobius r a d i c i s i n rearing, (a) Feeding l a r v a , (b) Prepupa i n pupal c e l l . Eighty-four H. r a d i c i s , 73 H. pales and 42 P. appro-ximatus were reared i n t h i s manner from egg to a d u l t . The larvae thrived on the inner bark and t h e i r development corresponded very c l o s e l y to that of fre e populations i n the f i e l d . Although m o r t a l i t y of reared larvae was as high as 50fo during the ea r l y stages of experimentation, the tech-nique was eventually improved to the point where l e s s than 5f<> of the larvae were l o s t . Most of the data on the seasonal h i s t o r y of H. pales were obtained from white pine trees, the preferred host, one of which was f e l l e d and set up as trap logs near i t s stump every two weeks during f i v e months of the 1956 grow-ing season. The trees, which were between 4 and 5 inches i n diameter and formed part of a dense stand, were cut i n 3-foot sections and placed h o r i z o n t a l l y on the ground. The logs and roots of each tree were sampled and weevil develop-ment was recorded weekly u n t i l pupae began to form under the bark. At t h i s time the stump and main root system were ex-cavated and placed i n outdoor screen cages. About 6 inches of s o i l was kept over the stumps to prevent d e s i c c a t i o n , pine bark f r e s h l y removed from trees was used i n the cages as, traps f o r the emerging adults which were c o l l e c t e d d a i l y . None of the logs set up i n the f i e l d were s u c c e s s f u l l y i n -fested by the weevil, and they were discarded. Ten Scots pine trees were used i n a s i m i l a r fashion to study the seasonal h i s t o r y and habits of P„approximatus. The feeding habits of H. -pales were studied on natural regeneration i n the study plantations and on potted plants d i s t r i b u t e d i n a g r i d p a t t e r n i n a two-acre area cut over the previous f a l l i n which the stumps were i n f e s t e d with H. p a l e s . Equal numbers ( s i x of each species) of four-year-old white pine, red pine, A u s t r i a n pine, P. nigra Am., and Scots pine plants were set out. The feeding damage were ob-served and tagged at weekly i n t e r v a l s . Measurment of Damages The e f f e c t of r a d i c i s damage on pine growth was studied 16 by comparing height and radial growth increments of infested and non-infested twenty-year-old trees, and by controled infestations on caged ten-year-old trees. To facilitate accurate determination of the effect of weevil attack on the tree, 40 healthy Scots pines averaging about ten years of age, were transplanted in October of 1955 to a heavily in-fested area. These trees were grown at the Midhurst Nursery as ornamental stock and had been pruned yearly for over five years so that although the diameter of the stem at ground level was between two and three inches, they did not exceed four feet in height. In May 1956, 24 of the trees were selected randomly and enclosed individually in screen cages measuring four feet square by five feet in height (Pig. 3 ) . In early June, 1956 the caged trees and the so i l within each cage was sprayed thoroughly with ethylene dichloride, a fumigant, i n order to k i l l any weevils present. After the poisonous effects of the insecticide had dissipated (about two weeks),, the 24 caged trees were randomly divided into three groups of eight trees and infested with two mated pairs of young adult weevils (four insects) to each tree as follows; group one on June 19, 1956; group two on July 17, 1956; and group three on May 23, 1957. One tree from each group of infested trees and two from the checks were removed monthly during the 1956 and 1957 growing seasons and examined 17 F i g . 3. Caged pine trees used i n studying the bionomics of Hylobius r a d i c i s . f o r damage and weevil population at the root c o l l a r . The e f f e c t of H. r a d i c i s on the growth of pines was investigated during the summer of 1955. In a mixed stand of 20-year-old white, red, and Scots pines heavily i n f e s t e d with the weevil since 1950, 10 white pines, 20 red pines, and 20 Scots pines were cut and t h e i r annual height and r a d i a l increments measured f o r the period 1945 to 1955. Since only the white pines i n the stand were not i n f e s t e d 18 with the weevil, t h e i r measurements were used as an i n d i c a t i o n of normal growth over the ten year period considered and as a check on the growth of the two other h e a v i l y i n f e s t e d species. The trees were a l l cut i n June and ear l y J u l y at a time "before Hhe new adults emerged so that an accurate count of the weevil population on each tree could be made. From sections (discs) cut at the root c o l l a r s of t e n he a v i l y i n f e s t e d Scots pines and ten red pines that had rece n t l y been k i l l e d by H. radicis« i t was po s s i b l e to de-termine the f i r s t year each tree was attacked and, roughly, the progress made by the weevils u n t i l the death of the t r e e . During the 1955, 1956, and 1957 growing seasons, 78 Scots, pines and 60 red pines i n f e s t e d with Hi r a d i c i s were examined i n order to determine the extent of damage, the number and d i s t r i b u t i o n of the d i f f e r e n t stages i n the v i c i -n i t y of the root c o l l a r , and to determine the cause and extent of m o r t a l i t y w i t h i n each stage as the season pro-gressed. 19 HYLOBIUS RADICIS BUCH. Hylobius r a d i c i s Buchanan (16) BIOLOGY: F e l t (30, 31, 32, 33, 34, 37 ( p a l e s ) , 39, 40, 41, 42, 43, 45, 47), York (126 ( p a l e s ) ) , Glasgow (60, 61), plumb (90, 91, 92), F e l t and Bromley (49» 50, 51), Maxwell and Mac-Leod (78), Schaffner (104, 105, 106, 108), Schaffner and Mc Intyre (109), Craighead (20), Shenefelt (111), ISallace (120), Prentice (94), 1/lktson (123), Finnegan (52), Warren (121). H i s t o r y : H. r a d i c i s was described i n 1934 by Buchanan (16) f o l l -owing several reports by F e l t (30, 31, 32, 33, 34, 37) and York (126) describing a new type of weevil damage on Scots pine, red pine, and p i t c h pine, P. r i g i d a M i l l . , i n the State of New York, which they believed was caused by the pales weevil. From 1934 to 1942, several short reports on the hosts, d i s t r i b u t i o n and damage caused by H. r a d i c i s were made by F e l t (37, 41, 43, 47), F e l t and Bromley (49, 50, 51), Glasgow (60, 61), Maxwell and MacLeod (78), Plumb (89, 91, 92), and Schaffner (104, 105, 106, 108). In 1944, Schaffner and Mc-Intyre (109) discussed the l i f e h i s t o r y , habits, economic 20 importance, and con t r o l of the species i n the New England States, s t a t i n g that the weevil was a serious pest of Scots pine, Austrian pine, and i t s v a r i e t y Corsican pine. They also noted that heavy i n f e s t a t i o n s were observed only where the trees were growing i n l i g h t sandy s o i l s as reported e a r l i e r by P e l t and Bromley (49). Schaffner and Mclntyre stated f u r t h e r that i n f e s t a t i o n s were also observed i n jack pine, Mugho pine» P. mugho Turra., p i t c h pine, red pine, and eastern white pine, but that serious i n j u r y occured to these species only where they were growing near i n f e s t e d Scots or A u s t r i a n pines. In 1950 Shenefelt (111) presented a paper on the chemical c o n t r o l of the weevil i n Wisconsin. In Canada, the f i r s t record of H . r a d i c i s was made by iallaeje (120) i n 1954, who reported up to 25$ m o r t a l i t y i n Scots and red pine plantations i n f e s t e d by the weevil i n southern Ontario. The fo l l o w i n g year 1/latson (123) presented a morphological d e s c r i p t i o n of the f u l l grown l a r v a of the weevil, and Prentice (94) reported damage to red pine and jack pine i n Manitoba, that l a t e r proved to be an i n f e s t a t i o n of t h i s species. In 1956 Pinnegan (52) discussed b r i e f l y the damage caused by H . r a d i c i s i n a s s o c i a t i o n with H j . pales and P. approximatus i n southern Ontario. The o r i g i n of the weevil i n Manitoba was b r i e f l y discussed by l/parren (121) i n 1956. 21 Description of Lif e History Stages; ADULT: The adult H. radicis i s robust, measuring from 9.4 to 13.0 mm. i n length and from 3.7 to 5.2 mm. i n width (Fig. 4,, d). The weevil i s dark brown and i s marked irregu-l a r l y on the thorax and elytra with spots of cream coloured, scale-like hairs. The beak i s stout and about as long as the prothorax, with the antennae attached s l i g h t l y i n front of the middle. It resembles closely H. pales, and although Buchanan (16) gives a considerable l i s t of minute differences between the two species, he summarises these as follows: "aside from the narrower male uncus, the characters of radicis that appear to be distinctive, i n comparison with pales, are the larger size, the lack of scaly spot on forehead and the spotted, rather than barred elytra." Since a l l of these characters intergrade, i t i s very d i f f i c u l t to separate a large percentage of the weevil population. In the f i e l d , the best macroscopic characters that can be used to separate the two species with some degree of accuracy, i s the larger body size and spotted elytra of H. radicis as contrasted with the smaller body size and barred elytra of H. pales ( f i g . 5). The male H. radicis i s about 1.5 mm., shorter than the female. It also differs from the female i n three main charac-ters; f i r s t , the uncus of the hind t i b i a i s stouter and di s t i n c t l y flattened i n the male, while that of the female F i g . 4. Hylobius r a d i c i s . (a) Egg x24; (b) Larva x6 (e) Pupa i n earthen c e l l x6; (d) Adult x6. 23 F i g . 5. Dorsal view of (a) Hylobius r a d i c i s and (b) H. •pales, showing the scattered spots on the e l y t r a of H. r a d i c i s i n c o n t r a s t to the b a r r e d p a t t e r n on the e l y t r a of H. p a l e s . 24 i s c o n i c a l ( F i g . 6 a, c ) ; second, the f i r s t and second ab-dominal sternites, of the male are more or l e s s concave along the median l i n e , while i n the female they are convex ( F i g . 6 d); t h i r d , i n the male the middle part of the f i f t h abdominal s t e r n i t e e x h i b i t s a c i r c u l a r impression d i s t i n g u i -shing i t from the l a t e r a l parts ( F i g . 6 d). EGGs The egg i s e l l i p s o i d a l and measures 1.92 ± 0.10 mm. i n length and 1.15 ± 0.05 mm. i n diameter ( F i g . 4 a ) . I t i s opaque and d u l l creamy white i n colour. LARVA* The l a r v a i s t y p i c a l l y c u r c u l i o n i d i n form ( F i g . 4 b ) . Ihen f u l l y grown i t i s about 15 nun. i n length with a l e g l e s s white body, dark-brown head and black mandibles. The width of the head capsules of the 84 larvae reared i n the insectary were measured a f t e r each moult from the egg to the pupa. F i g . 7 i l l u s t r a t e s the d i s t r i b u t i o n of these measurments separated by sex, as they developed through each i n s t a r . Seven larvae ( a l l females) pupated a f t e r a minimum of f i v e i n s t a r s ; 45 (23"males- and: 22. females) required s i x i n s t a r s ; and the remaining 52 (23 males and 9 females), seven i n s t a r s before pupating. Although there i s a large overlap between the s i z e of head capsules of males and females i n each i n s t a r , the mean value f o r the females i s c o n s i s t e n t l y l a r g e r than that of F i g . 6 . (a) Hind t i b i a l uncus of Hylobius r a d i c i s males; (b) Hind t i b i a l uncus of H. pales males; (c) Hind t i b i a l uncus of H. r a d i c i s and H. pales females and (d) Abdominal impressions found on H. r a d i c i s and H. pales males. 27 1 0 0 1.50 2 . 0 0 2 . 5 0 HEAD C A P S U L E WIDTH IN MM. F i g . 7 . D i s t r i b u t i o n of head capsule measurmehts of 8 4 Hylobius r a d i c i s larvae reared i n the insectary from the egg to the a d u l t . The cross-hatched areas represent the overlap between adjacent i n s t a r s . the males i n corresponding i n s t a r s . This trend continues to the adult and accounts f o r the l a r g e r average s i z e of the females i n the adult population. While the head capsule measurments of the reared larvae f a l l i n t o a d i s t i n c t c l a s s f o r each of the f i r s t s i x i n s t a r s , the measurments of 4 7 6 larvae c o l l e c t e d i n the f i e l d during two growing seasons give l i t t l e or no i n d i c a t i o n 28 1.50 2.00 HEAD CAPSULE WIDTH IN MM. P i g . 8. D i s t r i b u t i o n of head capsule measurments of Hylobius r a d i c i s , representing (a) 476 larvae c o l l e c t e d i n the f i e l d ; (b) 84 larvae reared i n the ins e c t a r y . of the number of i n s t a r s present. The d i s t r i b u t i o n of these measurments i s shown i n p i g . 8. The d i f f i c u l t y experienced i n f i n d i n g the f i r s t and second i n s t a r larvae i n the bark i s l a r g e l y responsible f o r the small number of these i n d i -v iduals i n the sample, while the r e l a t i v e l y l a r g e r prepupal stage i s responsible f o r the large number of prepupae c o l -l e c t e d . The lack of r e s o l u t i o n of head capsule measurments of larvae c o l l e c t e d i n the f i e l d i n t o classes according to i n s t a r s i s to be expected where such a large number of i n -st a r s i s present. The influence of the environment on the growth of the weevils, p a r t i c u l a r l y those that overwinter i n the l a r v a l stage, i s great, and i t i s only under r i g i d l y c o n t r o l l e d r e a r i n g conditions that s u f f i c i e n t l y uniform l a r v a l development occurs to reveal the basic growth pattern, PUPAs The pupa i s completely white when f i r s t formed (Pig, 4 c ) . The eyes and mandibles t u r n black about the eight or ninth day, and the rostrum, prothorax, and legs darken to medium brown about two weeks a f t e r pupation. D i s t r i b u t i o n and Hosts? Since 1934, H. r a d i c i s has been reported i n Minnesota, Wisconsin, Pennsylvania, Massachusetts, Connecticut, New York, and V i r g i n i a i n the United States, and i n Manitoba and Ontario i n Canada (16, 32, 69, 94, 109, H I , 120). In Ontario the weevil has been found throughout Simcoe County and i n two other widely separated areas - Sault Ste. Marie 30 and Petawawa. Schaffner and Mclntyre (109) report the f o l l o w i n g trees as host plants? In southern Ontario, i t was found i n f e s t i n g Scots pine, red pine, A u s t r i a n pine, Mugho pine, and jack- pine, but was never found on white pine. Trees of a l l ages with a root c o l l a r i n excess of 1-^- inches may be attacked. Seasonal History? In southern Ontario, H. r a d i c i s overwinters i n the l a r v a l , pupal, and adult stages. Young overwintered adults o v i p o s i t from e a r l y May u n t i l September, and then u s u a l l y overwinter again to l a y eggs during a second season ( P i g . 9)» A few of the larvae a r i s i n g from eggs l a i d i n e a r l y May complete t h e i r development i n time to pupate i n September and overwinter as a d u l t s . Prom a t o t a l of 84 eggs reared i n the insectary, 11 developed to adults i n one season (before the end of September), while the remainder overwintered as larvae to pupate i n l a t e June and e a r l y J u l y of the next Pinus s y l v e s t r i s L. " nigra Am. " banksiana Lamb. Scots pine. A u s t r i a n pine. Jack pine. Mugho pine. P i t c h p i n e . Red pine. Eastern white pine. mugho Turra. r i g i d a M i l l . resinosa A i t . strobus L. 31 STAGE WIN. MAY JUNE|JULY AUG. SEPT. OCT. 1 WIN. MAY JUNE JULY AUG. SEPT. OCT. WIN. ADULT P m EGG 1 s LARVA -1B"~ - m PUPA 1 " n ADULT — • ' I — :  EGG H 11 LARVA III I 1 1 PUPA HI; ^.„„:„':„,.,:.:':!:J:^,.:. ADULT n ft P i g . 9. Seasonal h i s t o r y of Hylobius r a d i c i s i n southern Ontario. year. Schaffner and Mclntyre ( 1 0 9 ) report a two-year l i f e cycle f o r the species i n the New England States, but do not mention the p o s s i b i l i t y of part of the population having a one-year l i f e c y c l e . The e a r l i e s t egg found i n the f i e l d was on May 2 , 1 9 5 5 , while i n the ins e c t a r y o v i p o s i t i o n took place as ea r l y as mid-April i n 1 9 5 8 . The number of eggs l a i d v a r i e s g r e a t l y between females. Whereas some females l a y only a 32 few eggs,, others may lay as many as 40 in one season. In the insectary, the average number of eggs laid per female was. 17.5 during the f i r s t season and 14.2 during the second season. None of the reared females survived a third winter. During the peak of the egg-laying period (early July) an > active female may lay up to four eggs in one day, but the average was, found to be slightly less than one per day per female. Prom a total of 256 eggs incubated in the insectary 74» or 29$, did not hatch. Table I shows the average duration of each of the instars for five-, six-, and seven-instar larvae, as well as for the egg and pupal stages, of weevils reared in an unheated insectary during the summer months. It should be noted, however, that in the f i e l d the larvae overwinter in a l l but the f i r s t two instars and the period of these over-wintering instars are thereby much prolonged. Owing to the lengthy oviposition period, the larval population consists of a mixture of different sized larvae throughout the year. The rate of development of overwintered larvae is modified in nature, however, to produce a concentration of prepupae in late June. This means that larvae overwintering in an advanced state of development (sixth and seventh instar), by delaying their time of pupation, permit the younger individuals to catch up in their development, with the result 33 that the overwintered l a r v a l population pupates over a short period i n e a r l y J u l y . During the l a t t e r part of the summer, TABLE I The duration of the immature stages of Hylobius. r a d i c i s reared i n an unheated i n s e c t a r y during the summer season Stage ' Time (days) Egg : 14.5 ± 1.2 1st i n s t a r j 8.6 ± 1.0 2nd i n s t a r • 8.3 ± 1.9 3rd i n s t a r : 9.5 ± 1.3 4th i n s t a r : 11.8 ± 1.5 5th i n s t a r (Prepupa) '. 27.5 ± 6.2 5th i n s t a r ! 17.0 ± 4.0 6th i n s t a r (Prepupa) I 31.0 ± 6 . 8 6th i n s t a r \ 24.1 ± 4.4 7th i n s t a r (Prepupa) : 28.2 ± 5.1 Pupa : 19.8 ± 4.6 i n August and September, a few pupae can be found, but these have a r i s e n from eggs l a i d e a r l y i n the spring of the same year and not from overwintered l a r v a e . The e a r l i e s t pupa found, i n the f i e l d was on June 20, 1957. Habits? The adults u s u a l l y overwinter i n crevices i n the outer bark of the stem of l i v i n g pine trees, at or s l i g h t l y below ground l e v e l , but a small number overwinter i n the duff at the base of the tree s . In southern Ontario, the overwintered adults become ac t i v e during the l a t t e r part of A p r i l and apparently spend most of t h e i r l i v e s i n and around the root c o l l a r of the host t r e e , mating and o v i p o s i t i n g from e a r l y May to mid-September. The eggs are often l a i d i n the s o i l as f a r as. two inches from the tree, but u s u a l l y they are placed i n feeding wounds made by the adults i n the inner bark of the root c o l l a r . T/1/hen the eggs hatch, the young larvae are very a c t i v e and begin searching f o r food immediately. I f the eggs are l a i d close to the cambium of the tree, the larvae experience no d i f f i c u l t y i n e s t a b l i s h i n g themselves. When a tree i s f i r s t attacked, the young larvae feed mostly i n the inner bark, although the surface of the wood i s also s l i g h t l y scarred. The feeding i s confined to i s o l a t e d areas around the root c o l l a r that u s u a l l y become e l l i p t i c a l i n shape with the long axis running p a r a l l e l to the g r a i n of the wood. They increase i n siz e as the larvae develop and i n large trees are u s u a l l y r e - i n f e s t e d by the larvae of succeeding F i g . 10. Section through the root c o l l a r of a s i x - i n c h Scots pine showing t y p i c a l wounds caused by Hylobius r a d i c i s larvae. This tree had been infested f o r at l e a s t t h i r t e e n years. generations. Thus the trunk at the root c o l l a r becomes f l u t e d , since the undamaged cambium grows beyond the i n j u r y on e i t h e r side of the wound ( F i g . 10). Eventually, as the i n f e s t a t i o n increases, the tree becomes completely g i r d l e d 36 F i g . 11. Hylobius r a d i c i s damage "to the root c o l l a r of Scots pine, (a) Root c o l l a r of inf e s t e d tree with the p i t c h -i n f i l t r a t e d s o i l p a r t l y removed to show a l a r v a i n the outer bark; (b) Stump of in f e s t e d tree with s o i l completely removed to show swelling at the root c o l l a r due to l a r v a l damage; (c) Stump of in f e s t e d tree with bark removed from the root c o l l a r to show the extent of damage to the wood. and death follows (Pig. 11 o). I f the tree i s healthy and vigorous, i t responds to the l a r v a l damage by producing copius quantities of resinous sap at the s i t e of the i n j u r y so that large pockets of gum are formed. Advanced larvae are apparently well adapted to l i v i n g i n t h i s environment, f o r they are often found completely immersed i n the s t i c k y sub-stance. I t apparently becomes necessary, however, to r e l i e v e the sap pressure p e r i o d i c a l l y , and larvae accomplish t h i s by digging c i r c u i t o u s tunnels several inches i n length i n t o the s o i l , thus leading some of the sap away from the i n j u r e d area. Consequently, i n a h e a v i l y i n f e s t e d tree the s o i l surrounding the root c o l l a r soon becomes soaked with r e s i n f o r a distance of up to two or' three inches from the tree (P i g . 11 a ) . TSBien the larvae are f u l l y grown they make a f i n a l journey i n t o the s o i l up to two inches from the tree and there construct pupal c e l l s i n which they pupate ( P i g . 4 c ) . Occasionally the c e l l i s constructed i n the gum-soaked outer bark. P i g . 12 shows the d i s t r i b u t i o n of larvae and pupae found i n the s o i l surrounding the root c o l l a r s of i n f e s t e d t r e e s . The pupal c e l l i s u s u a l l y made with i t s long axis v e r t i c a l , or s l i g h t l y i n c l i n e d to the v e r t i c a l . Its depth varies from s o i l l e v e l to about ten inches below the surface. The l a r v a covers the i n s i d e of the c e l l with a cement-like substance (possibly r e s i n from the t r e e ) , F i g . 12. D i s t r i b u t i o n of Hylobius r a d i c i s larvae and pupae i n the s o i l around the root c o l l a r of i n f e s t e d Scots pines. 10 XL n.,, n a AUG. TIME OF YEAR Pig. 13. Emergence of Hylobius r a d i c i s adults from twenty trees during the summer of 1955. which binds the grains of sand i n t o a hard s h e l l - l i k e s t r u c t u r e . I t then remains i n a c t i v e f o r about one week before pupating. The newly formed callow adults remain i n a c t i v e i n t h e i r pupal c e l l s from one to two weeks before emerging from the s o i l . In June, 1955> twenty heavily i n f e s t e d stumps from three to four inches i n diameter were dug up, each with a one-foot b a l l of earth around the root c o l l a r , and placed i n cages f o r emergence observations. Fresh bark was placed i n each cage weekly during the emergence period to a t t r a c t the weevils as they emerged from the s o i l and d a i l y c o l l e c t i o n s were made from the bark. F i g . 13 shows 41 the emergence p a t t e r n of the 96 weevils c o l l e c t e d - 46 of which were males and 50 females. The young adults begin feeding almost immediately a f t e r emerging from the s o i l . They feed on the inner bark of the trunk i n the v i c i n i t y of the root c o l l a r and o c c a s i o n a l l y , at night, on the tender bark of twigs and small branches of healthy t r e e s . However, the adult population i n the f i e l d i s never s u f f i c i e n t l y large to cause serious feeding damage. The feeding damage i s quite conspicuous on branches, appear-ing as small open p i t s about i n diameter that often coalesce to form l a r g e r wound areas, i n a natural stand, the rate of spread of the weevil i s not rapid since adults emerg-ing from the root c o l l a r of a l i v i n g tree u s u a l l y remain to continue and increase the i n f e s t a t i o n on that p a r t i c u l a r t r e e . However, i n i n f e s t e d pine p l a n t a t i o n s , where heavy cuts are made p e r i o d i c a l l y , the weevils emerging from a stump or dead tree must of necessity f i n d new l i v i n g m a t e r ial on which to feed and o v i p o s i t , producing a more rapid spread of the weevil than i s otherwise experienced. This f a c t was established by s e t t i n g out bark traps from e a r l y May u n t i l mid-September i n both a h e a v i l y i n f e s t e d Scots pine stand and i n a r e c e n t l y cut-over area where the i n f e s t e d stumps had been l e f t i n the ground. No weevils were found on the bark traps i n the i n f e s t e d stand - i n d i c a t i n g a l a c k of 42 migration - while a large number was c o l l e c t e d from the bark traps placed i n the stump area. L i m i t i n g Factors? In southern Ontario, H. r a d i c i s i s found i n epidemic numbers only i n areas where exotic pines (mostly Scots and Au s t r i a n pines), are grown extensively. The weevil w i l l attack open-grown Scots pine as he a v i l y as Scots pine grown i n a dense stand. However i t was never found on native pines, even i n dense stands, i s o l a t e d from exotic pines. Where a stand of pure red or jack pine grows adjacent to an i n f e s t e d stand of Scots pine, only the marginal red and jack pines become i n f e s t e d . In mixed stands of native and exotic species on the other hand, a l l the trees are susceptible to i n f e s -t a t i o n . While stand composition and density are apparently c r i t i c a l f a c t o r s l i m i t i n g weevil population per tree on native pines, they do not seem to be important to weevil d e n s i t i e s on exotic species. T h i s is, probably due to physio-l o g i c a l d i f f e r e n c e s i n the two groups of pines. Throughout the year the weevil population on Scots pine was almost 50f0 higher than on red pine of s i m i l a r s i z e , even where i n f e s t a t i o n s were heavy and the two species grew i n close proximity to each other. F i e l d observations showed 43 that adult females o v i p o s i t i n g on red pine l a i d as. .many eggs as those o v i p o s i t i n g on Scots pine, hut that the c o e f f i c i e n t of d e s t r u c t i o n f o r the immature stages d i f f e r e d f o r popula-tions breeding on these two hosts» In both pines the greatest m o r t a l i t y occurred i n the egg stage and during the e s t a b l i s h -ment of the newly hatched l a r v a e . In the i n s e c t a r y i t was found that about 30$ of the eggs l a i d d i d not hatch. Apart from t h i s i n i t i a l l o s s , a large number of eggs are subjected to p o s s i b l e predation by mites and other s o i l scavengers, since approximately 25$ are deposited i n the s o i l as f a r as three inches from the t r e e . I t was not p o s s i b l e to determine accurately the extent of t h i s hazard, but l a r v a l counts of f i r s t - i n s t a r larvae i n the s o i l around the root c o l l a r of i n f e s t e d trees kept i n cages in d i c a t e d that i n both red pine and Scots, pine about 20$ of the v i a b l e eggs were destroyed before they hatched. The v i a b l e eggs l a i d i n niches i n the inner bark of the root c o l l a r , on the other hand, are w e l l protected by plant t i s s u e s and j u i c e s and s u f f e r l i t t l e or no m o r t a l i t y from predation. The newly hatched larvae are a c t i v e and may l i v e up to four days without eating. Therefore, larvae emerging from eggs l a i d i n the s o i l are u s u a l l y able to reach l i v i n g t i s s u e of the near-by root c o l l a r before s t a r v i n g . I t i s while attempting to e s t a b l i s h i t s e l f i n the cambium of the 44 l i v i n g tree that the l a r v a l population s u f f e r s i t s greatest m o r t a l i t y . The flow of sap from the f r e s h l y wounded root c o l l a r i s very pronounced and i n Scots pine k i l l s up to 60$ of the young larvae, while i n red pine as much as 75$ of the larvae are k i l l e d at t h i s time. Once the larvae have succeeded i n e s t a b l i s h i n g them-selves i n the l i v i n g t i s s u e s of the root c o l l a r , they are we3Ll protected from the environment, since they are almost always completely surrounded by large quantities of s t i c k y r e s i n which acts as an excellent p r o t e c t i o n against predators and p a r a s i t e s . The l a r v a l stage i s p r a c t i c a l l y free from p a r a s i t e attack. During the whole study period only two larvae c o l l e c t e d i n the f i e l d were found to be p a r a s i t i z e d . Three parasites emerged from these two larvae and were iden- v \ V > t i f i e d as Coeloides sp_. The pupa i s w e l l protected i n the pupal chamber. The c e l l w a l l , although hard and cement-like, i s not impervious to moisture, however, and when prolonged p r e c i p i t a t i o n occurs during the pupal period, f l o o d i n g may cause the death of the occupants. During the month of July, 1956, 4.42 inches of r a i n f e l l i n the Angus area as compared with an average of 2.77 inches f o r the previous 45 years. The following week a check was made on the condition of the pupae i n " the s o i l and i t was found that about 15$ died from drowning. The small, pupal population that enters hibernation i n the f a l l s u f f e r s heavy m o r t a l i t y due to low temperatures. In November, 1957, about 85$ of the pupae were dead i n t h e i r chambers, while i n A p r i l of the fol l o w i n g spring m o r t a l i t y had r i s e n to over 95$ . The adults spend nearly t h e i r whole l i v e s i n the duff surrounding the root c o l l a r of pines on which they feed and o v i p o s i t . In t h i s environment they are r e l a t i v e l y f r e e from the e f f e c t of climate and attack by predators. Death i n t h i s stage occurs mostly during the overwintering period. Out of an i n i t i a l population of 67 young adults reared from pupae during the summer of 1955, H » or 16$, died during the f i r s t winter and 41, or 61$, during the second winter. These adults were overwintered i n an unheated insectary i n cages contain-ing s i x inches of s t e r i l i z e d sawdust. During the summer of 1956 a f t e r adult emergence from i n f e s t e d stumps kept i n cages had ceased, the s o i l surrounding the stumps wqs examined f o r adults that had f a i l e d to emerge from, t h e i r pupal chambers. I t was found that 21$ of the new adults, had died i n t h e i r c e l l s and were i n f e s t e d with a green external fungus and a white i n t e r n a l fungus. The green fungus was i d e n t i f i e d as a saprophytic B e n i c i l l i u m sp. but e f f o r t s ^ to grow the white fungus on e i t h e r a r t i f i c i a l media or l i v i n g insects i n the laboratory f a i l e d and i d e n t i f i c a t i o n was not p o s s i b l e . The m o r t a l i t y of the immature stages of H. r a d i c i s i s summarized i n Table I I f o r both red and Scots pines. TABLE I I M o r t a l i t y of immature Hylobius r a d i c i s , c a l c u -l a t e d from populations on 60 red pines and 78 Scots pines and expressed as a percent of the i n i t i a l egg population. Host ; M o r t a l i t y (percent) I Egg '' [ Larva Pupa red pine : 41.8 \ 45.0 \ 2.0 Scots " 1 43.2 i » * \ 35.4 1 2.8 E f f e c t on the Tree? H. r a d i c i s w i l l attack healthy trees from l i - inches i n diameter at stump height (6 inches above ground), to mature trees measuring as much as two feet i n diameter at breaat height. Scots pines measuring l e s s than 4" dbh. are normally k i l l e d a f t e r three or four years of heavy i n f e s t a -t i o n , while red and jack pines can withstand the attack f o r one or two years longer. Pines that are l a r g e r than 4" dbh. when f i r s t attacked are seldom completely g i r d l e d , although t h e i r root c o l l a r s may be s e r i o u s l y weakened. SIGNS AND SYMPTOMSs The f i r s t external symptom of the tree to weevil attack consists of sap escaping from the wounded root c o l l a r i n t o the surrounding s o i l , producing a compactLlayer of p i t c h - i n f i l t r a t e d s o i l often two or three inches i n thickness over the whole damaged area ( P i g ; 11 a ) . Under the resin-soaked s o i l the outer bark of the stem i s us u a l l y w e l l preserved, although often separated from the sound wood by as much as one inch of gummy semi-hardened r e s i n mixed with l a r v a l f r a s s . I t i s i n t h i s l a y e r that most of the l a r v a l population i s found; In a h e a v i l y i n f e s t e d t r e e , removal of the outer bark and the gummy r e s i n around the root c o l l a r reveals a g r e a t l y reduced stem with only a small amount of cambium br i d g i n g the damaged area ( P i g . 11 c) The tree may remain a l i v e and vigorous under these conditions f o r s e v e r a l years. The large quantity of sap covering the wound creates a moist s e p t i c condition favourable to the pl a n t ; However, trees that are open-grown or at the edge of stands are very susceptible to windthrow and snowbreak and us u a l l y l e a n h e a v i l y i n the d i r e c t i o n of the p r e v a i l i n g winds (P i g . 14). Although windthrow has not yet occurred exten-s i v e l y i n dense stands i n southern Ontario, i t i s conceiv-able that should exceptionally strong winds occur, t h i s type of damage would be commonplace, f o r trees measuring 6" dbh. heavily i n f e s t e d with H. r a d i c i s f o r f i v e to ten years can us u a l l y be pushed over by two men without great d i f f i c u l t y . F i g . 14. Hylobius r a d i c i s damage, (a) A he a v i l y i n f e s t e d twenty-year-old Scots pine p l a n t a t i o n ; (b) Two infested trees broken at the root c o l l a r and blown over by wind. 49 When the tree i s completely g i r d l e d , there i s a r e l a -t i v e l y short period during which the colour of the f o l i a g e changes from green to a pale yellow followed by a red and then brown colouration; EFFECT ON GROWTHS The e f f e c t of H. r a d i c i s damage on the growth of pines was studied by measuring the annual height and r a d i a l increments of twenty-year-old Scots, red, and white pines f o r the period 1945 to 1955» An average of 10.1 and 9»7 immature weevils were found on the Scots and red pines r e s p e c t i v e l y , showing that the trees were h e a v i l y attacked, but none of the white pines were i n f e s t e d . Twenty Scots and 20 red pines, h e a v i l y i n f e s t e d since 1950, and 10 non-infested white pines were measured. F i g . 15 shows the average growth of these trees, both i n height and r a d i a l l y . When the growth curves of the Soots and red pines are examined i n d i v i d u a l l y , there i s no i n d i c a t i o n of a reduction i n growth from 1950 to 1955» except f o r the height increment of Scots pine which drops s l i g h t l y . The apparent l a c k of e f f e c t on these two pines by weevil attack was f u r t h e r empha-sized by the normal length and colour of t h e i r needles and the general healthy appearance of the crowns. B l a i s (4) states that the f i r s t year of growth suppres-s i o n of balsam f i r and white spruce, Picea glauca (Moench) Voss, h e a v i l y d e f o l i a t e d by the spruce budworm, Choristoneura F i g . 15. Growth curves of 20 reel pines and 20 Scots pines, h e a v i l y i n f e s t e d with Hylobius r a d i c i s , and 10 healthy white pines growing i n a mixed stand. The trees were a l l 22 years o l d . DATE ( Y E A R S ) fumif erarta Clem.,, several years i n succession, can be i n d i -cated by growth r a t i o s obtained by d i v i d i n g the average annual increment of the a f f e c t e d species by the average annual growth increment of non-infested species growing i n the same area^ He considers, the apparent f i r s t year of growth supression to be the one showing a growth r a t i o l e s s than that of any of the preceeding years, followed by a s e r i e s of d e c l i n i n g r a t i o s . Table I I I shows the annual growth r a t i o s TABLE I I I Growth r a t i o s f o r 20 Scots pines and 20 red pines h e a v i l y i n f e s t e d with Hylobius r a d i c i s . Year Scots pine Red pine' Radial [ ' . growth : Height growth | Radial growth ! Height growth 1945 1 [? 1 , 5 5 ' : 1.44 ' ; 0.75 '  , 0.95 1946 \ 1 , 5 2 1.04 ' 0.85 1947 | 1.07 ' 1.89 ' 0.98 ' 1.25 1948 . t 1.26 \ 1.50 ! 1 , 3 5 1.08 1949 [ 1.85 ' 1.64 1.35 1950 ; 1.54 ' 1.62 i 1.64 [ 1.16 1951 | 1.17 1.10 | 1.56 0.86 1952 0.80 0.92 \ 0.92 1955 [ 0.65 | 0.75 ' 0.80 ' 0.71 1954 ' 0.70 ', 0.95 1.06 53"-for the Scots and red pines obtained i n this manner. It can be seen fnom the ratios that there i s an apparent reduction i n the growth of the two infested species from 1951 to 1955. then B l a i s 1 c r i t e r i o n i s applied to the data i n Table III, the f i r s t year of suppression for Scots pine i s apparently 1951 for height growth and 1952 for radial growth, This i s true also for red pine i f the small ratios for height growth i n 1946 and radial growth i n 1945 are ignored. The growth ratios for the year 1954 a l l show slight increases suggesting a recovery of the affected species from weevil attack during that year. It should be kept i n mind, however, that Blais* analysis of the effect of C. fumiferana on the growth of balsam f i r and white spruce might not be applicable to the effect of H. radicis on pines. The marked differences that exists between the two types; of damages could be reflected i n the growth of the respective hosts. The trees studied by Blais had suffered almost complete defoliation for several consecutive years before dying, while the pines attacked by H. radicis maintained healthy crowns throughout the period of observation. Prom sections (discs) cut at the root collars of i n -fested pines, i t was. found that Scots pines attacked at the age of four or five years were k i l l e d about three or four years l a t e r , while trees attacked when 10 to 15 years of F i g . 16. Hylobius r a d i c i s damage, showing altern a t e rows of l i v i n g i n f e s t e d red pines and dead Scots pines. age died a f t e r s i x to eight years of i n f e s t a t i o n . In general red pines remained a l i v e about three years longer than Scots pines i n the same area. In stands where Scots pines and red pines are planted i n alterna t e rows t h i s i s very s t r i c k i n g , f o r the e a r l y death of the Scots pine creates a contrast with the apparently healthy red pines as shown i n F i g . 16 56 HYLOBIUS PALES (HBST.) Curculio pales Herbst (66). Hylobius pales Boheman (6, 7), Leconte (75, 76), Provancher (96), Harrington (62, 63), Blatehley and Leng (5). a s s i m i l i s Roelofs (99). pissodes macellus Germar (58), Leconte (75). BIOLOGY: Harris (64, 65), P i t c h (53), Le Baron (74), Dodge (23), Smith (112), Packard (79, 80, 81), Thomas (119), Saunders (100, 101), Hopkins (70), P e l t (27, 28, 29, 30, 31, 32, 33, 34, 37, 38, 44, 46, 47), Hinds (68), Carter (17), Brues (15), Peirson (82, 83, 84, 85, 86, 87), B r i t t o n (12), Wells (124), Anon (1), B r i t t o n and Zappe (14), Craighead (19, 20), D i e t r i c h (21, 22), K n u l l (72), York (126), Glasgow (60, 61), Schaffner (103, 107), P e l t and Bromley (49), Friend (54), Lyle (77), Robinson (97, 98), Savley (102), Bourne (8), P r i c o (95), Conklin (18), Eddy (26), Hetrick (67), Friend and Chamberlin (57), Beal and M c C l i n t i c k (2), Bess (3), S e n t e l l (110), Holt (69), Ebel and Speers (25), Speers (lt-4, 115), Thatcher (118). 57 History; H. pales was described i n 1797 by Herbst (66) and placed i n the genus Curculio. In 1834, Boheman (6) transferred i t to the genus Hylobius which had recently been described by Germar (58). During the century that followed Herbst's des-cription, the weevil was not considered to be of economic importance and was mentioned only b r i e f l y by Pelt (27), Pitch (53), Harris (64, 65), Packard (79, 80, 81), and Thomas (119). It was not u n t i l Carter (17) i n 1916 and Peirson (82) i n 1921 pointed out i t s role i n limiti n g white pine regeneration i n cut-over areas by feeding on the tender bark of seedlings, that the importance of the insect was f u l l y realized. Carter (17) reported that H. pales was a very important factor i n limiting the reproduction of conifers i n and around cut-over areas of white pine i n the Harvard Porest at Petersham, Mass. He stated that due to the feeding of pales adults, as much as 70$ of the young regeneration had been k i l l e d during the f i r s t two years following clear cutting of white pine. He concluded that i t was unwise to plant cut-over pine lands during the f i r s t two seasons after cutting operations, because the weevil population remained high i n the area for at least that length of time. He warned further, that i n planting pasture land with conifers large pines i n the area should not be cut before the planting because the seedlings i n the 58 v i c i n i t y of the stumps would he subjected to heavy feeding by the weevil and the r e s u l t i n g l o s s would produce open areas i n the p l a n t a t i o n . He maintained that H. pales damage to c o n i f e r regeneration would l i k e l y be heavier i n areas where the shelterwood method of c u t t i n g was used, since the f i n a l c u t t i n g a f t e r the regeneration had become established would produce breeding material f o r a l a r g e population of weevils. He stated that i n j u r y to pine reproduction could a l s o be ex-pected where s t r i p c u t t i n g was p r a c t i c e d , e s p e c i a l l y where the s t r i p s progressed from leeward to windward, since weevil damage was almost i n v a r i a b l y found as f a r as 100 yards from the edge of the old stand. peirson»s (82) paper i n 1921 presented the l i f e h i s t o r y and control of H. pales f o r the State of Massachussets. He discussed at some length the h i s t o r y , d i s t r i b u t i o n and host plants,, seasonal h i s t o r y , habits, and c o n t r o l of the weevil; More recent papers by B e a l and M c C l i n t i c k (2), Bess (3), Savely (1020» S e n t e l l (110), and Wells (124) have pointed out the continued importance of the weevil as a f o r e s t pest and have shown that i t i s found over most of the United^ States east of the M i s s i s s i p p i and north of F l o r i d a , and from Nova Scotia to Manitoba i n Canada; In r e p o r t i n g t h e i r observations on H. pales i n j u r y to white pine plantings i n Few. England i n 1942, Friend and Chamberlin (57) stated that 59 i n addition to the size and density of the young trees, the number of stumps present and the proximity of the trees to them i s important, and that the amount of damage i n an area i s dependent to some extent on the presence or absence of new areas i n the v i c i n i t y attractive to the weevil. If new areas did not materialize!,~f the adults usually remained i n the original area to hibernate and cause further damage the following spring. In 1957, Ebel and Speers (25) discussed the population levels of pine weevils i n North Carolina during the growing season following cutting, and stated that nearly 90$ of the specimens collected were H. pales. They concluded that the use of traps to determine weevil abun-dance i n the f i e l d was promising and deserved further study. Speers (114, 115) also discussed controls for the weevil with dips and sprays. Description of L i f e History Stages; ADULT $ The adult H. pales i s robust, measuring from 5.8 to 11.3 nim. i n length and from 2.1 to 4.5 mm. i n width (Pig. 17)% and closely resembles H. rad i c i s. The prothorax and elytra are usually conspicuously marked with spots of cream coloured scale-like hairs. In most individuals the e l y t r a l spots are arranged i n two definite groups or bars which divide the elytra into three sub-equal parts. The composite bars are oblique to the median line of the body and can also b Pig. 17. Hylobius pales adult xlO. be seen from the sides (Pigs. 5 h, 17). The strength of the bars vary greatly, some individuals exhibiting no definite pattern. The spots on the elytra of H. radicis, on the other hand, are never displayed i n bars (Pig. 5 a ) . As stated previously, no d i f f i c u l t y i s experienced i n 61 separating the males., of the two species by the shape of the hind t i b i a l uncus (Pi g . 6 a, b ) . The females, however, are very s i m i l a r and unless the e l y t r a l markings, average s i z e , and amount of scales present on the fr o n t of the head are t y p i c a l f o r each species, i t i s not po s s i b l e to separate them with c e r t a i n t y . The three secondary sex characters des-cribed f o r H. r a d i c i s a l so apply to H. pales ( P i g . 6). EGG? The egg i s e l l i p s o i d a l and measures 1.10 ± 0^07 mm. i n length and 0.68 ± 0.04 mm. i n diameter. It i s opaque and d u l l creamy white i n colour. I t i s only i n t h i s stage that H. pales, and H. r a d i c i s can be completely separated, since the eggs of H. r a d i c i s are almost twice as large as those of H. pales. LARVA$ The l a r v a i s t y p i c a l l y c u r c u l i o n i d i n form and when f u l l y grown measures about 12. mm. i n length. I t has a l e g l e s s white body, dark brown head, and black mandibles. At present i t i s impossible to separate, morphologically, the larvae of H. pales from those of H. r a d i c i s , except f o r the f i r s t i n s t a r H, pales l a r v a e , which are smaller than the smallest H. r a d i c i s l a r v a e, and the l a r g e s t H. r a d i c i s larvae (seventh i n s t a r ) which are l a r g e r than the maximum s i z e attained by H. pales, larvae^ Out of 73 larvae reared i n the ins e c t a r y from egg to ui 30 -:.50 HEAD CAPSULE WIDTH IN MM. P i g . 18. D i s t r i b u t i o n of head capsule measurments of 73 Hylobius pales larvae reared i n the insectary from the egg to the adu l t . The black area represents the measurments of the f i f t h i n s t a r larvae that continued development to a s i x t h i n s t a r before pupating. adult, 33 were males and 40 were females. P i g . 18 i l l u s t r a t e the d i s t r i b u t i o n of measurments of head capsule widths of these larvae separated by sex as they developed through each i n s t a r . It can be seen from the graph that most of the larvae pupated a f t e r f i v e i n s t a r s , but that 16 males and 18 63 females required s i x i n s t a r s before pupating. Simple c a l c u l a t i o n s comparing the r a t i o of the means of the head capsule widths of successive i n s t a r s show that t h i s r a t i o i s r e l a t i v e l y constant f o r the f i r s t f i v e i n s t a r s of both males and females, but that between the f i f t h and s i x t h i n s t a r s i t increases considerably (Table IV). Thus TABLE IV Comparison between observed head capsule widths of Hylobius pales larvae and those estimated by using Dyar's Rule Sex : Instar-Observed measurments \ Calculated \ widths | widths [ r a t i o s | (Dyar's Rule) :.  Male ; I t II | I I I i IV ! Y ! VI i 0.68 ' ! 0.94 - 1.37 ; 1.82 2.18 0.72 : j 0.73 ; 0.69 '. 0.76 ; 0.83 . 0.68 ; 0.94 1 1.31 ; l . 8 l 1 2.51 I : 0 . 5 1 ! 0.68 II ] 0.75 ; 0.72 0.71 Female < III ! 1.06 \ 1.01 [ 1.52 ! 0.69 ! 1.42 IV 1 • 0.76 ' I 2.00 V ! 2.00 2.43 ! 0.82 ! VI ! 2.81 • 64 the mean of the s i x t h i n s t a r i s cl o s e r to the mean of the f i f t h i n s t a r , f o r each sex, than i s indicated by Dyar's Rule. The cause of the increase i n the r a t i o becomes evident when the larvae of the s i x t h i n s t a r are traced back to t h e i r proper p o s i t i o n s i n the f i f t h i n s t a r * The shaded areas under the f i f t h i n s t a r i n P i g . 18 represents these larvae and they are seen to be the smaller i n d i v i d u a l s of that i n s t a r . This means that the s i x t h i n s t a r larvae are not representative of the f i f t h i n s t a r i n head capsule width and consequently have a mean width l e s s than i s predicted by Dyar's r u l e . I t i s of fur t h e r i n t e r e s t that since the s i z e of the adult i s c l o s e l y r e l a t e d to the s i z e of the prepupa, as shown i n P i g . 19, the smaller u s u a l l y l e s s vigorous larvae, by con-t i n u i n g t h e i r development to a s i x t h i n s t a r before pupating, u l t i m a t e l y produce the l a r g e r adults i n the weevil popula-t i o n . PUPA? The pupa i s completely white when f i r s t formed, but the eyes and mandibles turn black and the rostrum, pro-thorax, and legs darken to medium brown before changing to the a d u l t . D i s t r i b u t i o n and Hosts? Peirson (82) stated that the d i s t r i b u t i o n of H. pales 1.4 1.5 1.6 I.V 1.8 1.9 2.0 2.1 2.2 2.3 2 . 4 2.5 2.6 2.7 SIZE OF PREPUPA HEAD CAPSULE IN MM. P i g . 1 9 . Relationship between the head capsule s i z e of prepupae and adults of Hylobius pales. The regression l i n e Y = 0.413X + 0 . 8 8 9 has been f i t t e d to the data. was general throughout the eastern h a l f of the United States and i n southeastern Canada. He pointed out that since t h i s range was greater than the range of the weevil's f a v o r i t e food plant, white pine, other trees must n e c e s s a r i l y be used as food and breeding m a t e r i a l . This was l a t e r shown to be true by several workers (2, 21, 25, 9 7 , 102, 110) who reported the weevil feeding on southern pines and other conifers i n northern F l o r i d a , Alabama, and M i s s i s s i p p i During the past 50 years the f o l l o w i n g trees have been reported as adult food plants (2, 17, 57, 82, 124) s Pinus strobus L. Eastern white pine. " r i g i d a M i l l . P i t c h pine. M resinosa A i t . Red pine. ponderosa Laws. Ponderosa pine. " s y l v e s t r i s L. Scots pine. " taeda L. L o b l o l l y pine. » echinata M i l l . Shortleaf pine. " p a l u s t r i s M i l l . Longleaf pine. " v i r g i n i a n a M i l l . V i r g i n i a pine. " mugho Turra. Mugho pine. M cembroides Zucc, Cembra-pine• L a r i x l a r i c i n a (Du Roi) K. Koch Tamarack. » decidua M i l l . European l a r c h . Picea rubens Sarg. Red spruce. " abies (L.) Karst. Norway spruce. Abies balsamea (L.) M i l l . Balsam f i r . Tsuga canadensis. (L.) Carr. Eastern hemlock. Pseudotsuga m e n z i e s i i (Mirbel) Franco Douglas f i r . Juniperus communis L. Dwarf juniper. " v i r g i n i a n a L. Red juniper. Cupressus a r i z o n i e a Green. Arizona cypress. Cedrus deodara (Roxb.) Loud. Deodar cedar. Betula. p o p u l i f o l i a Marsh. Wire b i r c h . Fraxinus americana L. White ash. However, Carter (17), P e i r s o n (82), and Friend and Cham-b e r l i n (57) agree that white pine i s the p r e f e r r e d food p l a n t . In southern Ontario the weevil has been found feeding on white pine, red pine, jack pine, A u s t r i a n pine, Scots pine and tamarack. Although feeding occurs on the branches of large trees, the trees s u f f e r l i t t l e or no damage a f t e r they have reached a height of about ten f e e t . 67 I t has not been c l e a r l y stated, however, i n what pla n t s the weevil breeds. Several authors r e f e r to pines and spruces as s u i t a b l e breeding m a t e r i a l ( 5 » 5 7 , 82, 124), but only white pine, p i t c h pine, ponderosa pine, mugho pine, and cembra pine have been named s p e c i f i c a l l y as probable hosts of the immature stages (2, 5» 57 , 82). In southern Ontario, H. pales, adults.were reared from stumps , of red piney jack pine, and Scots pine, as w e l l as-from white pine. White pine stumps, however, were found to support almost twice,,as many weevils, as the red, jack, or Scots pine stumps of ...similar s i z e . Seasonal History? According to Peirson (82), H. pales adults emerge.from hibernation about mid-May i n Massachusetts and feed u n t i l about mid-June, at which time they migrate to an area where there i s s u i t a b l e breeding m a t e r i a l . He indicated that o v i -p o s i t i o n begins about J u l y 1, that the r e s u l t i n g larvae pupate about September 1 to emerge as adults about October I, and that they feed f o r twp or three weeks before entering hibernation, thus completing one generation per year. Although Peirson does not elaborate the p o i n t , he concluded, on the basis of larvae having been found as l a t e as October 8, that some i n d i v i d u a l s undoubtedly pass the winter i n the l a r v a l or pupal stage i n stumps or l o g s . Beal and M c C l i n t i c k (2) 68 P i g . 20. Seasonal h i s t o r y of Hylobius pales i n southern Ontario. questioned Peirson's d e s c r i p t i o n of the seasonal h i s t o r y , and stated that i n North Carolina there i s "one complete generation and a p a r t i a l second overlapping generation annually". In southern Ontario, H. pales overwinters i n both the adult and l a r v a l stages ( P i g . 20). Approximately 70$ of the summer larvae pupate and emerge as adults from late-August to mid-October to overwinter a f t e r a short feed-ing period. The remaining 30$ overwinter i n the l a r v a l stage. 69 Head capsule measurments of 27 overwintering larvae c o l l e c t e d l a t e i n November indicated that they overwinter only i n the f i f t h and s i x t h i n s t a r s . These larvae continue development during the fol l o w i n g spring and emerge as. adults from about mid-June to August 1. Only a few eggs are l a i d by these e a r l y adults during the current summer. In the f a l l the earl y adults merge with the main adult population to over-winter i n the s o i l , u s u a l l y at the base of young pla n t s on which they were feeding. The overwintered adults emerge from hibernation i n l a t e A p r i l and e a r l y May and feed f o r about two months before o v i p o s i t i n g . The f i r s t egg l a i d i n the insectary i n 1958 was on June 12; the general o v i p o s i t i o n period l a s t e d u n t i l the end of July, although one female l a i d three v i a b l e eggs on August 30 a f t e r being i n a c t i v e f o r over four weeks. Rearing experiments showed that adult weevils are long-l i v e d ; about 35$ overwintering twice, the females o v i p o s i t i n g during two successive growing seasons. The females l a y about 30 eggs, or 60$ of t h e i r t o t a l quota, during the summer fol l o w i n g the f i r s t overwintering period as ad u l t s , and about 18, or 40$, during the second summer. In 1957 the f i r s t summer l a r v a was found i n the f i e l d on July 6. The l a r v a l period l a s t s f o r about 47 days, followed by a pupal period of about 22 days. Table V shows the average duration of each of the i n s t a r s f o r both f i v e -and s i x - i n s t a r larvae, as well as f o r the egg and pupal stages, of weevils reared i n an unheated in s e c t a r y during the summer months. In southern Ontario the f i r s t pupa to \ appear i n the f i e l d i n 1957 was on August 26. The newly formed adults remain i n t h e i r pupal c e l l s about two weeks before emerging through the bark and s o i l . The peak of adult emergence i s about the l a s t week of September. TABLE V The duration of the immature stages of Hylobius -pales reared i n an un-heated in s e c t a r y during the summer season Stage ! Time (days) Egg 9.9 ± 1 . 3 1st i n s t a r j 5 . 3 ± 0.8 2nd i n s t a r j • 5.0 ± 0.8 3rd i n s t a r j \ 5.1 ± 0.7 4th i n s t a r s \ 6.5 * 1.0 5th i n s t a r (Prepupa) s • 20.8 ± 2.2 5th i n s t a r i . 9 . 3 i 1.4 6th i n s t a r (Prepupa) j \ 2 1 . 3 ± 2.8 Pupa , 21.8 ± 1 . 3 Habits$ The adults overwinter i n the duff and s o i l at the foot of the small tree or seedling on which i t was feeding. They are often gregarious at t h i s time of year and may be found i n small groups u s u a l l y under such objects as wood chips, small rocks, or the roots of t r e e s . In southern Ontario, they become ac t i v e i n e a r l y May at which time they emerge from the s o i l and continue t h e i r feeding at night on the tender bark of seedlings and small branches of l a r g e r trees throughout the growing season and then enter the s o i l to overwinter again. During th© egg l a y i n g season, the females enter the s o i l overlying the roots of f r e s h stumps and o v i p o s i t i n niches chewed i n the inner bark of the roots and the part of the stump below ground l e v e l . The female l a y s her eggs e r r a t i c a l l y , sometimes l a y i n g two or three i n one day, followed by several days of i n a c t i v i t y , during which time i t feeds on healthy pines above ground^ The eggs are u s u a l l y deposited s i n g l y , but sometimes two or'three are placed together i n s i n g l e niches chewed by the female. The newly hatched larvae feed in" the cambial area of the roots or stump, s c a r r i n g the wood more deeply than the inner bark. The tunnels do not form a d e f i n i t e pattern i n the lower part, of the stump, but wander without respect to 72 •the g r a i n of the wood. In the roots, however, the tunnels always run with the gra i n , y/hen the larvae reach maturity they construct "chip cocoons" i n the wood about V i n depth and p a r a l l e l to the g r a i n . These c e l l s may be found i n the part of the stump l y i n g below ground l e v e l and throughout the root system where the roots are more than i " i n diameter. About 70$ of the larvae pupate i n the roots at a distance greater than one foot from the stump. A' few of the pupal c e l l s are made completely within the wood. When the pupal c e l l i s complete the l a r v a encloses i t s e l f within i t by s e a l i n g the entrance with long e x c e l s i o r - l i k e chips of wood obtained while digging the c e l l . A short prepupal p e r i o d of about three days follows, during which the prepupa i s i n a c t i v e . Although Pe i r s o n (82) and Savely (102) state that H. pales breeds i n pine logs as we l l as i n stumps, Beal and McC l i n t i c k (2) claim that t h i s i s not the case i n North Carolina, but that i t breeds only i n the roots and stumps of dying t r e e s . In southern Ontario, the adult weevils were at t r a c t e d to the underside of f r e s h l y cut pine logs, but only a few eggs were l a i d and none of the r e s u l t i n g larvae developed to maturity. This i s probably p a r t l y due to the low moisture content of the logs during dry periods, and p a r t l y to competition from immature stages of p. approximatus and Ips rjini(Say), a bark beetle that attacks f r e s h l y cut. 73 pine logs i n large numbers. In the ten study trees cut i n 1956, about 80$ of the H. pales larvae developed i n the roots of the stump, while the remaining 20$ developed i n the part of the stump below the root c o l l a r , i n and around the crotches of the main roots. Bark traps and potted seedlings set up i n the f i e l d showed that overwintered adults, feed and search f o r breeding material u n t i l about the t h i r d week i n June, and then devote most of t h e i r time to egg l a y i n g i n dead or dying stumps. The feeding damage i s l i g h t during J u l y and August, but becomes heavy again i n mid-September when the new. adults begin emerging. There are, therefore, two feeding periods per year, one i n the spring and one i n the f a l l . Following a c u t t i n g operation there are three feeding periods on surrounding regeneration before the weevil population subsides, as reported by Peirson (82)? the f i r s t i s i n the spring f o l l o w i n g the c u t t i n g , by adults a t t r a c t e d to the f r e s h l y cut stumps from the surrounding area; the second i s i n the f a l l of the same year a f t e r the new adults have emerged from the stumps; and the t h i r d i s i n the fol l o w i n g spring by the large adult population that overwintered i n the area. Peirson (82) states that there i s a mass f l i g h t period about mid-June from cut-over areas, p a r t i c u l a r l y i n the t h i r d year of i n f e s t a t i o n . This habit has not been noted i n south-74 e m Ontario. I t should be remembered, however, that P e i r s o n was r e f e r r i n g to weevil populations associated with lumbering operations, so that when the a v a i l a b l e breeding material was used up, the adult weevils had to move,,of necessity, to a new area f o r breeding purposes. In southern Ontario, on the other hand, the weevil i s associated mostly with Christmas tree p l a n t a t i o n s , where s e l e c t i v e c u t t i n g i s p r a c t i s e d and a continuous supply of breeding material i s a v a i l a b l e to the weevil. Under these conditions i t i s not necessary f o r mass migration to take place. L i m i t i n g Factors? In a pine stand where white pine, red pine, and Scots pine grow i n approximately equal numbers, white pine stumps were preferred over red and Scots pine stumps,as feeding and breeding m a t e r i a l . Throughout the season about 5 5 $ of the adult weevil population found i n the s o i l was on white pine stumps, while 2 9 $ and 16$ were on red and Scots pine stumps r e s p e c t i v e l y . Apparently the l a y i n g habits of the females are not a l t e r e d by the host, f o r the number of young larvae found i n the stumps were always i n proportion to the number of l a y i n g females i r r e s p e c t i v e of the host. Since the eggs are l a i d i n niches i n the inner bark of the stumps and roots, they are well protected from environ-75 mental hazards. The i n i t i a l l o s s of 23$ of the eggs due to f a i l u r e to hatch i s the only f a c t o r s e r i o u s l y a f f e c t i n g the egg population. In areas where the weevil population i s heavy, competi-t i o n f o r food i n the l a r v a l stage becomes serious and may cause the death of 70$ or more of the young l a r v a l population. Dendroctonus valens Lee., a bark beetle that attacks weak pine trees and f r e s h l y cut stumps, may at times almost com-p l e t e l y exclude the H. pales population from stumps. While the larvae are a c t i v e l y feeding they are r e l a t i v e l y f r e e from attack by mites. However, during the prepupal period, i f mites are successful i n entering the pupal chamber, they may i n f l i c t a s u f f i c i e n t number of wounds to k i l l the pre-pupa. About 2$ of the prepupae are k i l l e d i n t h i s manner. It i s only with d i f f i c u l t y that mites can enter the pupal c e l l s , f o r while the e x c e l s i o r - l i k e outer l a y e r of the "chip cocoon" i s e a s i l y penetrated, a second inner l a y e r of f i n e c l o s e l y packed wood dust i s p r a c t i c a l l y impenetrable. A Braeonid p a r a s i t e plays a minor r o l e i n c o n t r o l l i n g the weevil. The r a t i o between t h i s p a r a s i t e and adult weevils emerging from stumps kept i n cages, was about 1 % 200. M o r t a l i t y i n the adult stage was heaviest during the second overwintering p e r i o d . About 36$ of the young adult population emerging i n the f a l l died during the f i r s t winter and about 45$ during the second winter. The remainder died during the second growing season. None of the adults reared i n the insectary survived to enter a t h i r d period of h i b e r -nation. The most important l i m i t i n g f a c t o r of H. pales i s the quantity of a v a i l a b l e breeding m a t e r i a l i n the f i e l d . U n t i l recent years, damage to pines caused by the weevil has not been as extensive i n southern Ontario as reported i n the United States. This i s probably due to the f a c t that there had been no l a r g e - s c a l e c u t t i n g operations of pines i n the area f o r some time, thus preventing a buildup of the weevil population. Since 1945, however, the Christmas tree industry has expanded g r e a t l y and large c u t t i n g operations of s i x - , seven-, and eight-year-old trees have been made during the past few years. The stumps of these trees, l e f t i n the ground to r o t , were he a v i l y i n f e s t e d by H. pales with the r e s u l t that i t now occurs i n epidemic numbers i n Simcoe 'County and Durham County and generally i n the area west of a l i n e drawn through Port Severn and Trenton. In areas where the damage i s heaviest, up to 40$ of the branches of f i v e -to ten-year-old pines have been k i l l e d or discoloured over the whole stand (52). 77 E f f e c t on the Tree? H. pales adults w i l l feed on the tender hark of twigs and small branches of pines from the seedling stage up to mature t r e e s . Tyhere the weevil population i s high t h i s may r e s u l t i n the death of seedlings and young trees up to ten years of age, and of i n d i v i d u a l branches on l a r g e r t r e e s . The damage i s of p a r t i c u l a r importance to Christmas tree growers, f o r the market value of trees i s g r e a t l y lowered by the presence of damaged or dead branches. SIGNS AND SYMPTOMS? The feeding damage of H. pales i s very s i m i l a r to that of H. r a d i c i s . The adults chew - small p i t s about i n diameter through the bark to the wood. Where high populations exist;-..the p i t s are so numerous that they j o i n together to form l a r g e r wound areas that eventually g i r d l e the stem or branch. Oftentimes the bark of seedlings i s completely removed. Fresh damage may be i d e n t i f i e d r e a d i l y , but sap exuding from the wounds soon f i l l s up the small p i t s and upon s o l i d i f y i n g , hides them by covering the branches with r e s i n . Girdled branches and trees can be spotted e a s i l y at a distance by t h e i r brown colour. 78 PISSODES APPROXIMATES HOPK. Pissodes approximatus Hopkins (71). BIOLOGY: B r i t t o n (10, 11, 13) , Wells (124), Anon (1), Boving (9), Plummer and P i l l s b u r y (93), Knul l (72, 73), Peirson (88, 89), E a s t e r l i n g (24), P e l t (35, 36, 48), Plumb (90, 91), Schaffner (103), P e l t and Bromley (49, 50), Stewart (116), Priend (55, 56), Bess (3). History? P. approximatus was described i n 1911 by Hopkins (71), who stated that i t bred i n the th i c k bark of the tree , some-times causing serious damage to the s a p l i n g stage. In 1929, Boving (9) discussed the taxonomic differences between the mature larvae of p1. ^ approximatus and P. s t r o b i . Plummer and p i l l s b u r y (93) reported that although the breeding habits' of the two weevils d i f f e r e d t h e i r seasonal h i s t o r i e s were very similar,, and suggested that they might prove to be one species since they had been successful i n r e a r i n g P. s t r o b i experi-mentally i n the trunks of weakened tre e s . That they are indeed d i f f e r e n t species i s shown by the diffe r e n c e i n t h e i r chromosome numbers (S. G. Smith, unpub.,) and the absence from P, s t r o b i of the chromosomal polymorphism reported i n 79 P. approximatus (113). The importance of p. approximatus as a secondary pest i n areas where pines have been weakened by d e f o l i a t o r s , bark beetles, or by transplanting, has been pointed out by E a s t e r l i n g (24), P e l t (36), Schaffner (102), and Stewart (116). There i s at present only scant information a v a i l a b l e on the bionomics of t h i s weevil, and i t s present status i n the northeastern United States i s not c l e a r , although Holt (69) has reported that i t i s becoming an i n c r e a s i n g l y serious pest i n coniferous plantations i n the State of Pennsylvania. Description of L i f e H i s t o r y Stages; ADULT: The adult P. approximatus i s a t y p i c a l cur-c u l i o n i d and c l o s e l y resembles P. s t r o b i ( p i g . 21). I t varies considerably i n s i z e , being from 5 to 8 mm. i n length and from 2 to 3 mm. i n width. The females are, on the average, 1 mm. longer the males. The newly emerged adult i s medium brown, darkening to almost black a f t e r having overwintered. The prothorax, e l y t r a , and legs are marked with t u f t s of white and reddish-brown scales grouped to form several small spots on the prothorax and u s u a l l y two i r r e g u l a r bands across the e l y t r a . The curved snout i s slender and about as long as the prothorax, with the antennae attached about mid-way along i t s length. Hopkins (71) separates P. approximatus from p. than F i g . 21. Pissodes approximatus adult xl2. s t r o b i by the "average large s i z e , elongate body, the sides of the e l y t r a more d i s t i n c t l y narrowed p o s t e r i o r l y . The beak i s longer, the spots of the e l y t r a are uniformly smaller, the p o s t e r i o r ones r a r e l y connected". EGG: The egg i s ovoid and measures 0.80 ± 0.04 mm. i n length and 0.50 t 0.03 mm. i n diameter. The shape of the 2 < o a. UJ m •30 .46 .63 .79 .96 1.12 1.29 1.45 HEAD CAPSULE WIDTHS IN MM. Pig, 22. D i s t r i b u t i o n of head capsule measurments of pissodes approximatus larvae. egg varies considerably, some being almost spheroid. The volume of the egg, however, i s r e l a t i v e l y constant. When f i r s t l a i d i t i s almost c o l o u r l e s s with a smooth g l i s t e n i n g chorion, LARVA.: The l a r v a i s t y p i c a l l y c u r c u l i o n i d i n form, When f u l l y grown i t i s about 12 mm, i n length with a l i g h t brown head and a white body. The 42 weevils reared from eggs i n •the insectary a l l passed through four l a r v a l i n s t a r s . F i g . 22 i l l u s t r a t e s the d i s t r i b u t i o n of measurments of head capsule TABLE YI Comparison between observed head capsule widths of pissodes  approximatus larvae by using Dyar's Rule and on the basis of a l i n e a r regression r e l a t i o n s h i p Instar i Observed Dyar' s Rule ' Linear regression width Calcu- $ l a t e d : width j Per cent \ error s Calcu->, l a t e d ! width * Per cent error I J ! 0.354 • • : p;285 +19.5 II ! 0.512 • • * • 0.534 ? -4.3 \ ; 0.568 # 0* -10.9 II I 0.755 • • • 0.805 i -6.6 : 0.852 • -12.9 IV i I 1.218 $ * 1.215 I +0.2 ! t 1.135 » + 6.8 #> m * * * # • • width of reared larvae as they developed through each i n s t a r from the egg to the pupal stage. A. f i e l d check was made on the las.t i n s t a r by measuring the head capsules of 112 pre-pupae c o l l e c t e d i n the f i e l d from chip cocoons. The hatched polygon i n P i g . 22 represents these measurments and i n d i c a t e s good agreement with measurments of the reared m a t e r i a l . Table VI shows a comparison between the observed head capsule widths and those estimated using Dyar's Rule and on the basis of a l i n e a r regression r e l a t i o n s h i p . It i s evident that the increase i n width from one i n s t a r to the next follows Dyar's Rule more c l o s e l y than the l i n e a r regression suggested by Ghent (59) f o r c e r t a i n s a w f l i e s . PUPA? The pupa i s completely white when f i r s t formed, but the mandibles, eyes, rostrum, prothorax, and legs become medium brown before adult emergence. D i s t r i b u t i o n and Hosts? In h i s o r i g i n a l d e s c r i p t i o n , Hopkins (71) reported the following pines as host plants? Pinus strobus L. " r i g i d a M i l l . " banksiana Lamb. " echinata M i l l . " resinosa/JLit. " v i r g i n i a n a M i l l . " pungens Lamb. Eastern white pine. P i t c h pine. Jack pine. Shortleaf pine. Red pine. V i r g i n i a pine. Table mountain pine, It. has since been reported breeding i n Mugho pine (48) and Scots pine (90, 116). Hopkins recorded i t s d i s t r i b u t i o n as Wisconsin, Michigan, Pennsylvania, New York, Mew Hampshire, Massachusetts, V i r g i n i a , West V i r g i n i a , and North C a r o l i n a i n the United States, and southern Ontario i n Canada. Since 1911, P. approximatus has a l s o been recorded i n Connecticut (10) and Ohio (24). In Ontario, the author has c o l l e c t e d the weevil at widely scattered points throughout the southern STAGE WIN. MAY JUNE JULY AUG. SEPT. OCT. WIN. MAY JUNE JULY AUG. SEPT. OCT. WIN. ADULT HP 1 ^>^< EGG lip LARVA IP m PUPA • ADULT wk EGG IIP wk B 1 LARVA wk III i i PUPA lip « IP —™ ADULT lip • P i g . 23. Seasonal h i s t o r y of pissodes appro-ximatus i n southern Ontario. part of the province. Seasonal History? In southern Ontario, P. approximatus overwinters i n the l a r v a l , pupal, and adult stages. This, together with the f a c t that there i s a long o v i p o s i t i o n period, leads to a complicated seasonal h i s t o r y with generations of both 85 one and two years duration ( F i g . 23). The majority of the population overwinters i n the adult stage. The remainder overwinters i n the l a r v a l and pupal stages to emerge as adults i n l a t e June and Ju l y of the following year and over-winter once again. The overwintering adult population thus consists of the progeny of the previous winter^s overwinter-ing adults, plus adults developed during the previous summer from overwintered larvae and pupae. In the spring, over-wintered adults from these two sources are i n d i s t i n g u i s h a b l e . The f i r s t egg was found i n the f i e l d during the 1956 growing season on. May 26, while i n the insectary the f i r s t egg was l a i d on June 13. Most of the females l a y t h e i r quota of eggs before the end of the f i r s t week of J u l y and then d i e . The adult population i n the f i e l d , therefore, declines r a p i d l y early i n Ju l y , but a few females continue l a y i n g u n t i l early September. The developmental period of the 42 weevils reared from egg to adult i n 1956, was about 60 days. Table VII shows the average duration of the egg stage, the four l a r v a l i n s t a r s , and the pupal stage of in s e c t s reared i n an unheated i n s e c t a r y during the summer months. Habits? The adult weevils overwinter i n the duff and top s o i l 86 overlying the roots and under scales and i n crevices of the rough outer hark of pine t r e e s . They emerge i n ea r l y May and feed f o r about three weeks on the inner bark of pine branches and on the stem of seedlings and small t r e e s . The underside of low-lying branches i n contact with the l i t t e r are par-t i c u l a r l y a t t r a c t i v e as feeding s i t e s . TABLE VII The duration of the immature stages of Pissodes approximatus reared i n an unheated in s e c t a r y during the summer months Stage J Time (days) Egg • • 8.6 + 1.6 1st i n s t a r # «--0 3.6 + 0.5 2nd i n s t a r 3.9 + 0.8 3rd i n s t a r % 4.9 + 0.9 4th i n s t a r % 24.0 + 6.1 Pupa 14.8 + 0.7 «* During the l a t t e r h a l f of May, there i s a mass f l i g h t period when the weevils search f o r s u i t a b l e breeding m a t e r i a l . Mating takes place at t h i s time and o v i p o s i t i o n begins about l a t e May, Dead or dying trees of a l l age classes from one-87 and two-year-old seedlings to mature trees may be attacked from the roots up to branches as small as •§-" i n diameter. In seedlings, where the bark i s too t h i i t to accommodate mature larvae, the larvae bore to the center of the stem, where they pupate. The eggs may be l a i d throughout the trunk and large branches, but the rougher bark at the branch nodes seems to be p r e f e r r e d . In the insectary, 12 females l a i d an average of 49 eggs each, with one l a y i n g 102. The eggs are deposited, i n pockets; chewed i n the inner bark by the females. They are normally l a i d i n d i v i d u a l l y i n the pockets, but frequently groups of four or f i v e eggs may be found together. The newly hatched larvae are very small, measuring about 1 mm. i n length. Immediately upon hatching they begins feeding i n the cambial l a y e r . They normally mine i n e i t h e r d i r e c t i o n along the g r a i n of the wood unless interrupted by obstacles, i n which case they e i t h e r change d i r e c t i o n through o * 180 or work around the obstacle and continue with the g r a i n of the wood ( P i g . 24). y«4ien the larvae a t t a i n maturity, they construct chip cocoons t y p i c a l of the genus Pissodes i n the outer surface of the wood ( P i g . 25). Pupal development takes place i n these chambers and requires three or four days. Newly formed adults remain i n the pupal chambers about f i v e days before chewing t h e i r way to the outside, when the c u t i c l e 88 P i g . 24. Larva of pissodes app- roximatus i n rearing. Note l a r v a l mines p a r a l l e l to the grain of the bark. soon hardens and darkens to a medium brown. The f i r s t adult emerged i n cages i n 1 9 5 6 on J u l y 2 6 followed by a sustained high emergence from about August 1 5 to September 1 0 . The sex r a t i o of emerging adults was approximately 1 j 1 . The new adults feed from the time of emergence u n t i l the onset of cold weather, but the females do not mate or ovip o s i t u n t i l the following summer. Logs i n f e s t e d i n June, 1 9 5 6 , produced an average of 2 1 6 adults per square foot of bark, while logs i n f e s t e d i n P i g . 25. "Chip cocoons" of pissodes approximatus showing, (a) one c e l l i n t a c t and (b) another opened to reveal the prepupa i n s i d e . Note the e x c e l s i o r - l i k e covering of the c e l l s . 90 , 9 1 e a r l y September produced only 51 adults per square f o o t . I t must be remembered, however, that the r e l a t i v e percentage of each stage overwintering depends to a large extent on the time of the year the breeding material becomes a v a i l a b l e to the weevils. In southern Ontario, where large populations of the weevil are u s u a l l y associated with Christmas tree c u t t -ings, the stumps of trees cut i n the f a l l are invaded i n l a t e May and e a r l y June the f o l l o w i n g year, and t h i s r e s u l t s i n a large emergence of adults i n August and September, Breeding material a v a i l a b l e l a t e r i n the summer i s r e l a t i v e l y l i m i t e d , r e s u l t i n g i n only a few overwintering larvae and pupae?. L i m i t i n g Factors? Since P. approximatus i s a secondary insect incapable of a ttacking healthy pines s u c c e s s f u l l y , the main f a c t o r l i m i t i n g i t s population density i s the a v a i l a b i l i t y of s u i t -able breeding m a t e r i a l . Under natural conditions this, f a c t o r keeps the weevil population low. In areas where pines are grown i n pure stands and the stumps of harvested trees are l e f t i n the f i e l d to r o t , however, populations r a p i d l y b u i l d up to epidemic proportions. Several other f a c t o r s of l e s s e r importance operate i n c o n t r o l l i n g the population of p. approximatus. During the 92 P i g . 26. Stem of a three-inch red pine i n f e s t e d with Pissodes  approximatus (pupal stage). 1956 growing season up to 3 5 $ of the l a r v a l population was k i l l e d by a v i p i o n i d ecto-parasite belonging to the genus Coeloides. Sap suckers and woodpeckers are also of consider-able importance. They are capable of devouring large numbers of larvae, pupae, and adults from under the bark, p a r t i -c u l a r l y i n trees where the stem i s heavily infested through-out i t s length ( P i g . 2 6 ) . In I 9 5 6 the downy woodpecker, F i g . 27. Four-inch Scots pine stump i n -fested with pissodes approximatus and Hylobius  pales (pupal stage). The lack of pupal c e l l s above ground l e v e l i s due to competition from bark beetles. Dendrocopus pubescens medianus (Swainson), destroyed up to 90$ of the weevil population i n i n d i v i d u a l trees by com-p l e t e l y s t r i p p i n g the bark from the stem and large branches i n search of food. Weevil populations i n stumps, however, were found to be p r a c t i c a l l y free from attack by b i r d s ( F i g . 27); they are nevertheless subject to serious competition from two bark beetles, Dendroctonus valens Lec. and Ips  p i n i (Say), and H. pales. 94 E f f e c t on the Tree? Although P. approximatus normally breeds i n dead or dying pine m a t e r i a l , i t can s u c c e s s f u l l y attack seedlings ., and weak trees f o r breeding purposes, causing the pla n t s to d i e . This type of damage was p a r t i c u l a r l y noticeable i n seedlings of Au s t r i a n pine i n the Midhurst Nursery, where about 9fo were k i l l e d by the weevil i n 1956. Recently trans-planted f i v e - to ten-year-old ornamental stock was also heavily attacked i n the Angus area i n 1956 and 1958. SIGNS AND SYMPTOMS? Fresh feeding wounds made by P. app-roximatus are somewhat d i f f e r e n t from those made by H. r a d i c i s  a n ^ S» p a l e s . Ihereas the Hylobius adults chew i r r e g u l a r p i t s i n both the outer and inner bark, p. approximatus leaves the outer bark i n t a c t except f o r small punctures through which i t i n s e r t s i t s beak and chews out l a r g e r areas of the inner bark. This, makes the feeding damage of P. approximatus l e s s noticeable when i t i s f r e s h , but when the bark on the injured twigs become weathered the outer bark fl a k e s o f f and the feeding damage resembles that of the other species. 95 DISCUSSION AND CONCLUSIONS At the time when the present i n v e s t i g a t i o n s were under-taken, a v a i l a b l e information on H. r a d i c i s , H, pales, and P. approximatus was based mainly on observations made i n the New England States, Minnesota, and Wisconsin and applied to problems somewhat d i f f e r e n t from those i n southern Ontario, It became apparent at that time that conditions brought about p r i m a r i l y by the Christmas tree industry during the previous ten years were i d e a l f o r the buildup of large weevil popula-tions and that t h i s presented a serious threat to p l a n t a t i o n grown pines, whether planted as Christmas trees or i n county f o r e s t s . In the present work the previous information e x i s t i n g on the three weevils has been brought together and i n t e r p r e t e d i n the l i g h t of observations made i n southern Ontario, The ecology of the weevil complex has been investigated to the extent that the bionomics and cause of outbreaks are w e l l understood, and the main l i m i t i n g f a c t o r s of the weevil / • populations, are known. With t h i s newly acquired knowledge, i t i s p o s s i b l e to appraise the weevil problem i n southern Ontario i n a manner not possible p r e v i o u s l y , and to draw c e r t a i n conclusions and make recommendations on p r a c t i c a l methods of growing pines i n pure stands r e l a t i v e l y f r e e from weevil attack. B a s i c a l l y , the weevil problem i n southern Ontario i s of a s i l v i c u l t u r a l nature. The three weevils are native species and are not known to occur i n large numbers except where pines are grown i n pure stands or where large c u t t i n g operation of pines have taken p l a c e . H. r a d i c i s d i f f e r s i n habits from H. pales and P. approximatus mainly i n that i t attacks and breeds i n healthy pines, while the l a t t e r two species breeds only i n dead or decadent pine m a t e r i a l . Since H. r a d i c i s occurs i n epidemic number only i n puref stands where exotic pines such as Scots, Austrian, or mugho are present i n large numbers, one method of coping with the wee-v i l i s to avoid the p l a n t i n g of pines i n such mixtures. This i s not always d e s i r a b l e , however, f o r i n southern Ontario Scots pine has a greater market value as a Christmas tree than any other species and i s consequently grown extensively i n pure stands. In such areas i t may be necessary to c o n t r o l H. r a d i c i s by means other than s i l v i c u l t u r a l . I t was found i n the present studies that the a p p l i c a t i o n of b i o l o g i c a l controls would not be p r a c t i c a l , since a l l stages of the weevil are well protected from predators, p a r a s i t e s , and f u n g i . Stewart (117) reports that he obtained 100$ c o n t r o l of H. r a d i c i s i n f e s t i n g Scots pine i n southern Ontario, by applying a d i e l d r i n spray at the base of the t r e e s . He has 97 also communicated d i r e c t l y with the author that one a p p l i c a -t i o n of t h i s i n s e c t i c i d e i s e f f e c t i v e i n p r o t e c t i n g the trees from r e - i n f e s t a t i o n f o r a period of up to three years. The main objection to the chemical c o n t r o l suggested by Stewart i s that large quantities of water are needed f o r the spray. Since most pine plantations are located on high, well-drained, sandy s o i l s , the water problem i s of paramount importance and u s u a l l y ..prohibits the use of the recommended c o n t r o l . Therefore, a p r a c t i c a l c o n t r o l f o r H. r a d i c i s i n southern Ontario has not yet been achieved. This i s true p a r t i c u l a r l y i n county f o r e s t s where pines are planted to grow to maturity, f o r i n t h i s instance i t i s possib l e that several a p p l i c a t i o n of i n s e c t i c i d e would be needed during the l i f e of the tree to prevent r e - i n f e s t a t i o n . However, when considering pines grown f o r the Christmas tree market i t i s possib l e that one a p p l i c a t i o n of i n s e c t i c i d e would s u f f i c e . H. r a d i c i s w i l l not attack trees l e s s than 1-fe- inches i n diameter at stump height (6 inches above ground), and a tree of t h i s s i z e (usually four or f i v e years old) needs only three or four years p r o t e c t i o n before c u t t i n g f o r market. Since the area i n f e s t e d by H. r a d i c i s i n southern Ontario i s s t i l l a c t i v e l y expanding, i t was not p o s s i b l e to determine the f a c t o r s l i m i t i n g i t s d i s t r i b u t i o n . However, i t iwould'iseem that the s o i l exerts some influence on the 98 i n s e c t , f o r a l l known i n f e s t a t i o n s i n the area are confined to l i g h t sandy s o i l s of low f e r t i l i t y . This i s i n agreement with reports by,Schaffner and Mclntyre (109) i n the United States. Preliminary work done on the s o i l i n the Angus area during 1958 i n d i c a t e s that texture i s not the only f a c t o r involved, f o r the weevil i s conspicuously absent from c e r t a i n areas where the s o i l i s l i g h t and sandy, although heavy i n -f e s t a t i o n s abound i n the immediate v i c i n i t y . It i s p o s s i b l e that a combination of f a c t o r s such as texture, moisture con-tent, and s o i l r e a c t i o n are a c t i n g together i n l i m i t i n g the d i s t r i b u t i o n o:g the weevil. H. pales and p. approximatus both breed i n dead or decadent pine material and attack healthy trees only as adults f o r feeding purposes. Therefore, a large amount of breeding material i s necessary f o r the weevil to increase to epidemic numbers. In n a t u r a l stands where the weevil occurs i n small numbers, the feeding damage i s n e g l i g i b l e and u s u a l l y not noticed. I t i s the lack of a sound s a n i t a t i o n program i n Christmas tree plantations and county f o r e s t s that has brought about the present problem i n southern Ontario. The c u t t i n g methods used by Christmas tree growers poses serious problems to a sound s a n i t a t i o n program. Normally pines are cut as Christmas trees between the ages of s i x and nine years i n three successive years. The f i r s t 99 year a l i g h t cut i s made of the more advanced t r e e s . The second year a heavy cut i s made of most of the merchantable trees followed by a clean-up out i n the t h i r d year. Usually the area i s replanted during the f o u r t h year by plowing a furrow between the rows of stumps to receive the new p l a n t s . This means that f o r three consecutive years large numbers of f r e s h stumps are l e f t i n the ground to rot and be i n f e s t e d by H. pales and P. approximatus. Under t h i s c u t t i n g system the Christmas tree grower i s hesitant to p u l l stumps a f t e r the f i r s t and second cut f o r f e a r of damaging the remaining t r e e s . Furthermore, many plantations are located on land covered with large boulders over which a t r a c t o r could not be operated. In view of the f a c t that Christmas tree growers are hesitant i n p u l l i n g stumps a f t e r each cut f o r p r a c t i c a l as well as f i n a n c i a l reasons, an a l t e r n a t i v e s o l u t i o n to the s a n i t a t i o n problem i s d e s i r a b l e . I t i s p o s s i b l e that i n f e s -t a t i o n s would be prevented i f the stumps and roots of trees cut during the f i r s t and second year are kept a l i v e by l e a v i n g the bottom whorl of large branches on the stumps, and .then p u l l i n g a l l the stumps a f t e r the t h i r d cut with a bulldozer or t r a c t o r . In considering chemical controls of H. pales and P. approximatus t i t i s conceivable that an i n s e c t i c i d a l spray 100 applied -to the part of the stump above ground l e v e l , would k i l l the greater part of the P. approximatus population when i t emerges as adults. However, since over 60$ of H. pales pupate i n the roots at a distance i n excess of one foot from the stump and emerge d i r e c t l y through the s o i l , i t would be necessary to spray the s o i l overlying the roots as w e l l as the stumps to c o n t r o l t h i s species. In a Christmas tree p l a n -t a t i o n t h i s would mean spraying the whole ground once f o r every crop grown, f o r the root system of adjacent trees over-lap to a considerable extent. The large quantity of water and i n s e c t i c i d e needed f o r t h i s c o n t r o l makes i t unsuitable f o r general use and should be considered only as an emergency measure where a valuable crop w i l l be l o s t i f subjected to one more feeding season. Spraying the f o l i a g e of trees to protect the branches from adult feeding i s even more i m p r a c t i c a l , f o r an a p p l i c a t i o n of i n s e c t i c i d e would have to be applied every year to a l l the trees i n the stand. This would mean about eight a p p l i c a t i o n s per crop and would create an expense that the growers could not bear. Pl a n t a t i o n grown pine i s subject to attack by a number of destructive i n s e c t s . The weevil complex discussed i n t h i s t h e s i s i s , perhaps, the most recent such problem to a t t a i n economic importance i n southern Ontario. Since i n s e c t s u s u a l l y 101 become problematic wherever plants are grown i n concentrated numbers as a crop, i t often becomes necessary e i t h e r to f o r -mulate s u i t a b l e d i r e c t controls f o r the pests, or to d e s i s t the p l a n t i n g of pure stands. S i l v i c u l t u r a l controls are usu-a l l y more desirable than d i r e c t c o n t r o l s , f o r they tend to prevent insect outbreaks, while d i r e c t controls are generally applied only a f t e r the i n s e c t s have reached epidemic propor-t i o n s . There are reasons to believe that s i l v i c u l t u r a l con-t r o l s could be used s u c c e s s f u l l y against the weevils discussed here. In the Christmas tree industry, the p u b l i c demand f o r a s p e c i f i c species of pine or other c o n i f e r i s created l a r g e l y by the grower. In the Maritime Provinces the p r a c t i c e i s to grow balsam f i r ; i n southern Ontario Scots pine; and i n northern Ontario spruces. Strangely enough most of these trees are sold to a common d i s t a n t market i n the United States. I t i s the b e l i e f of the author that i t would be p r o f i t a b l e f o r growers to operate co-operatively, p l a n t i n g a crop of mixed conife r s instead of only one species. This would l i m i t g r e a t l y the ravages of several i n s e c t pests that have become i n c r e a s -i n g l y important i n plantations during the past f i f t y years, by reducing the density of t h e i r f a v o r i t e food or breeding m a t e r i a l . The weevil problem on pines i n southern Ontario s t i l l e x i s t s , and the Christmas tree industry i s s e r i o u s l y threa-102 tened i n several areas. There i s a need f o r f u r t h e r e c o l o g i -c a l i n v e s t i g a t i o n s to determine the importance of such f a c t o r s as s o i l , climate, stand composition, and management as they a f f e c t weevil density and the Christmas tree industry. 103 BIBLIOGRAPHY (1) ANON. 1927. The r e l a t i o n of i n s e c t s to slash d i s p o s a l . TJ. S. Dept. Agr., C i r c . 411. 12. (2) BEAL, J. A., AND K. B. McCLINTICK. 1 9 4 3 . The pales weevil i n southern pines. J. Econ. Ent., 36(5)? 792-794. (3) BESS, H. A. 1 9 4 4 . Insect attack and damage to white pine timber a f t e r the 1938 hurricane i n New England. J. Por., 42: 14-16. (4) BLAIS, J. R. 1958. E f f e c t s of d e f o l i a t i o n by spruce budworm (Choristoneura fumiferana Clem.) on r a d i a l growth at breast height of balsam f i r (Abies b a l - samea (L.) M i l l . ) and white spruce (Picea glauca (Moench) Voss.). por. Chronicle, 34(1): 39-47. (5) BLATCHLEY, ¥. S. AND C. W. LENG. 1916. Rhynchophora or weevils of North America. Indianapolis, 682. (6) BOHEMAN, C. H. 1834. In Schonherr's Genera et Species. Curculionidum I I . 340. (7) ' 1842. In Schonherr's Genera et Species. Curculionidum VI. 300. (8) BOURNE, A. I. 1940. Pales weevil (H. p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv. 20: 191. 104 (9) BOVING, A. G. 1929. Taxonomic characters f o r the i d e n t i f i c a t i o n of the mature larvae of pissodes  s t r o b i Peck, and Pissodes approximatus Hopkins (Pam. Curculionidae). Proc. Ent. Soc. Wash., 31(9)i 182-187. (10) BRITTON, W. E. 1918. Seventeenth report of the Conn-e c t i c u t Entomologist f o r 1917. Conn. A g r i . Expt. Sta., B u l l . 203. 231-370. (11) 1920. Nineteenth report of the Conn-ec t i c u t Entomologist f o r 1919. Conn. A g r i . Expt. Sta., B u l l . 218. 112-208. (12) 1925. Twenty-fourth report of the Conn-e c t i c u t Entomologist f o r 1924. Conn. A g r i . Expt. Sta., B u l l . 265. 340. (13) 1929. Twenty-eightA report of the Conn-e c t i c u t Entomologist f o r 1928. Conn. A g r i . Expt. Sta., B u l l . 305. 666-768. (14) BRITTON, W. E. AND M. P. ZAPPE. 1927. ^Hylobius pales H b s t ^ . Conn. A g r i . Expt. Sta., B u l l . 292. 163. (15) BRUES, G.I 1920. ^Hylobius pales HbstJ] . Ins. Human welfare. 81. (16) BUCHANAN, L. L. 1934. An apparently new species of North American Hylobius, with synoptic key (Coleop-t e r a : Curculionidae). Proc. Ent. Soc. Wash., 36: 105 252-2 56. (17) CARTER, E. E. 1916. Eylobius pales as a f a c t o r i n the reproduction of c o n i f e r s i n New England. Proc. Soc. Amer. Foresters, 2(3).s 297-307. (18) CONKLIW, J . G, 1941. Pales weevil (H. p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21; 110. (19) CRAIGHEAD, P. C. 1927.^Hylobius pales HbstJ . U. S. Dept. Agr., C i r c . 411. 4. (20) 1950. Insect enemies of eastern f o r e s t s . TJ. S. Dept. Agr., Misc. Pub. 657. 285-286. (21) DIETRICH, H. 193L Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. P l a n t Quar., Ins. Pest Surv., 11: 28. (22) 1932. Pales weevil (H. p a l e s ) . U. S. Dept. Agr,, Bur. Ent. plant Quar., Ins. Pest Surv. , 1 2 : 31. (23) DODGE, R. l874.£kylobius pales Hbst^J . Rural Caro-l i n i a n , V. 476. (24) EASTERLING, G. R. 1934. A study of the insect fauna of a coniferous r e f o r e s t a t i o n area i n south-eastern Ohio. Ohio J . S c i . , 34s 129-146. (25) EBEL, B. H. AND C. P. SPEERS. 1957. Population studies 106 on the -pales weevil (Hylobius p a l e s ) . Proc. Assoc. South. A g r i . Workers, 54 : 153-154. (26) EDDY, B. 1 9 4 1 . Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins Pest Surv., 2 1 : 2 0 8 . (27) PELT, E. P. 1906. Insects a f f e c t i n g park and woodland t r e e s . Mem. N.< Y. State Mus., 8 j 877 . .(28) 1 9 2 3 . ^Hylobius pales Hbst . J . N. Y. State Rept., 35? 8 6 . (29) 1924. In Manual of tree i n s e c t s . 2 2 9 . (30) 1926. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 6 : 1 7 2 - 1 7 3 . .(31) • 1926 . Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 6 : 2 9 6 . (32) 1926. Pales weevil i n a new r o l e . J . Econ. Ent., 1 9 ( 5 ) ; 7 9 5 . (33) 1928. Observations and notes on i n j u r i o u s and other i n s e c t s of New York State. N. Y. State Mus. B u l l . 2 7 4 . 145-176. (34) 1 9 3 1 . Pales weevil (H. p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 1 1 : 477. - « ' 107 (35) 1934. A pine weevil p. approximatus. U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 14? 204-205. (36) _. 1935. The important shade tree i n s e c t s i n 1934. J . Econ. Ent., 28(2)* 390-393. (37) ; , 1935. Pales weevil (Hylobius pales Boh.). U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 15s 386. (38) 1936. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 16s 487. (39) 1936. A weevil (Hylobius r a d i c i s Buchanan). TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 16$ 417. .. . . (40) 1938. Scotch pine weevil (Hylobius r a d i c i s Buch.). TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 18$ 22-23. (41) 1939. A weevil (H. r a d i c i s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 19s 405. (42) 1940. Pine root weevil (H. r a d i c i s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins..Pest Surv., 20$ 21... (43) 1940. A pine weevil (H. r a d i c i s ) . TJ. S. 108 Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 20$ 191. (44) 1941. Pales weevil (H p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21$ 54. (45) 194L A weevil - H. r a d i c i s . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21: 110. (46) 1941. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr,, Bur. Ent. Plant Quar., Ins. Pest Surv., 21s 208. 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Ent. ,PTe.ch. f.Ser., No. 20. 1-68. (72) KNOLL, J . N. 1931. Pales weevil (H. p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest :.  Surv., 11 j 220. (73) 1932. A pine weevil (P. approximatus). U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins.- Pest Surv., 12$ 113. (74) LeBARON, W. 1871. In p r a r i e Parmer. 42: (75) LECONTE, J . L. 1876. In Proceedings of -the American P h i l o s o p h i c a l Society. XV". 140. (76) 1885. In Transactions of the American Entomological Society. XII. 30. (77) LYLE, C. 1937. Pales weevil (H. p a l e s ) . U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 17$ 24. (78) MAXWELL, K. E. AND G, P. MACLEOD. 1937. A Scots pine weevil, Hylobius r a d i c i s Buchanan. J . Econ. Ent., 30s 215-216. 112 (79) PACKARD, A. S. 1878. Guide to the study of i n s e c t s . New York. 715. (80) 1881. In Insects i n j u r i o u s to f o r e s t s and shade t r e e s . TJ. S. Ent. Comm., B u l l . 7. 275. (81) 1890. Insects i n j u r i o u s to f o r e s t s and shade t r e e s . F i f t h Rept. TJ. S. Ent. Comm., 724. (82) PEIRSON, H. B. 1921. The l i f e h i s t o r y and con t r o l of the pales weevil (Hylobius p a l e s ) . Harvard For., B u l l . 3. 33p. (83) 1922. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 2? 144. (84) 1922. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 2$ 255. (85) 1923. Pales weevil (H. p a l e s ) . TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 3: 332. (86) 1923. In Maine f o r e s t service. B u l l . 1. 33. (87) 1927. In Maine f o r e s t s e r v i c e . B u l l . 5. 104. (88) 1931. A weevil (P. approximatus). TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest 113 Surv., 11: 477. (89) 1941. A weevil (P. approximatus). TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21 j 547. (90) PLUMB, Gr. H. 1936. A pine weevil (P. approximatus). U. S. Dept. Agr., Bur. 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