©lie Pmtarsti|j of ^rtttsij (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. ALLEN I. McT. COWAN J. E. BIER P. A. LARKIN V. KRAJINA DEAN W. H. GAGE 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. ALLEN I. McT. COWAN J. E. BIER P. A. LARKIN V. KRAJINA DEAN W. H. GAGE 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.

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RAYMOND JOSEPH FINNEGAN B. Sc. (F.) 1948, University of New Brunswick. M. Sc. (P.) 1950, University of New Brunswick.

A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

in the Department of Zoology

We accept this thesis as conforming to the required standard

THE UNIVERSITY OF BRITISH COLUMBIA September, 1958. ABSTRACT

Three native weevils have "become increasingly important

in recent years in stands of planted pines in southern Ont• ario. The pine root collar weevil, Hylobius radicis Buch.,

breeds in the root collar of healthy pines;, killing over

SO

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

pinest 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 measurment of body size and larval

feeding.

Stand density is the chief factor regulating popula•

tions 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 infes- iii

tation 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 recommendations to avoid pure dense stands especially of exotic species, and to practice forest sanitation in cutting operations. In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make

it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my

Department or by his representative. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission.

Department of

The University of British Columbia Vancouver 8, Canada. iv

CONTENTS

Page INTRODUCTION 1

TAXONOMY 4

METHODS 10

Study of Insect Biologies 10

Measurment of Damage 15

HYLOBIUS RADICIS BUCK 19

History 19

Description of Life History Stages 21

Distribution and Hosts 29

Seasonal History 50

Habits • 34

Limiting Factors 42

Effect on the Tree 46

HYLOBJJJS PALES (HBST.) 56

History 57

Description of Life History Stages 59

Distribution and Hosts 64

Seasonal History 67

Habits 71

Limiting Factors 74

Effect on the Tree 77 V

PISSODES APPROXIMATUS HOPE 78

History . .. 78

Description of Life History Stages t. 1... 79

Distribution and Hosts 83

Seasonal History 84

Habits t- i. 85

Limiting Factors *... i ... 91

Effect on the Tree' 94

DISCUSSION AND ^CONCLUSIONS .. ..; : 95

BIBLIOGRAPHY 103

FIGURES

Fig. 1. Method,;.of rearing pine weevils in the insectary from the egg to the adult stage showing, (a) pouring the sa'nd over the * inner bark and screen; (b) a sectional view of the rea'ring unit 12

Fig. 2. Larvae of Hylobius radicis in rearing (a) Feeding larva, (b) Prepupa in pupal -r cell 14

Fig. 3. Caged pine trees used in studying the bionomics of Hylobius radicis 17

Fig. 4. Hylobius radicis. (a) Egg x24; (b) Larva x6; (c) Pupa in earthen cell x6; (d) Adult x6 22

Fig. 5. Dorsal view of (a) Hylobius radicis and (b) H. pales, showing the* scattered spots'' on the elytra of H. radicis in contrast to the barred pattern on the elytra of H. pales ...... 23 vi

Pig. 6. (a) Hind tibial uncus of Hylobius radicis males; (b) Hind tibial uncus of H. -pales males; (c) Hind tibial uncus °f H» radicis and H. pales females and (d) Abdominal impressions found on H. radicis and H. pales males. .. . 26

Pig. 7. Distribution of head capsule measurments of 84 Hylobius radicis larvae reared in the insectary from the egg to the adult.. The cross-hatched areas represent the overlap between adjacent instars 27

Pig. 8. Distribution of head capsule measurments of Hylobius radicis, representing (a) 476 larvae collected in Jthe fieldV (b) 84 ' " larvae reared in the insectary...... 28

Pig. 9. Seasonal history of Hylobius radicis in southern Ontario. ... 31

Pig. 10. Section through the root collar of a six-inch Scots pine showing typical wounds caused by Hylobius radicis larvae. This tree had been infested for at least thirteen ye%rs. 35 pig. 11. Hylobius radicis damage to. the root collar of Scots pine, (a) Root collar of infested tree with the pitch-infil• trated soil partly removed to show a larva in the outer bark; (b)stump of infested tree with soil completely removed to show swelling at the root collar due to larval damage; (c) Stump of infested tree wi'th bark removed from the root collar to show extent of damage to the wood. 36

Pig. 12. Distribution of Hylobius radicis larvae and pupae in the soil around the root collar of infested Scots pines i.... 39 pig. 13. Emergence of Hylobius radicis adults from twenty trees during the summer of 1955 40 vii

Pig. 14. Hylobius radicis damage, (a) A heavily infested twenty-year-old Scots pine plantation; (b) Two infested trees broken at the root collar and blown over by wind. .48

Pig. 15. Growth curves of 20 red pines and 20 Scots pines, heavily infested with .-•- Hylobius radicis, and 10 healthy white pines growing in a mixed stand. The trees were all 22 years old 51

Pig. 16. Hylobius radicis damage, showing alier- nate rows of living infested red pines ••• and dead Scots pines 54

Pig. 17. Hylobius pales adult xlO 60

Pig. 18. Distribution of head capsule measurments of 75 Hylobius pales larvae reared in the insectary from the egg to the adult. The black area represents the measurments of the fifth instar larvae that continued development to a sixth instar before pupat• ing. 62

Pig. 19. Relationship between the head capsule size of prepupae and adults of Hylobius pales. The regression line Y = 0.413X + 0.889 has been fitted to the data. 65

Pig. 20. Seasonal history of Hylobius pales in

southern Ontario * 68

Pig. 21. Pissodes apprdximatus • adult xl2. 80

Pig. 22. Distribution of head capsule measurments of Pissodes approximatus larvae...... 81 Pig. 23. Seasonal history of pissodes approxi• matus in., southern Ontario. 84

Pig. 24. Larva of Pissodes approximatus in rearing. Note larval mines parallel'' to the grain of the bark V... 88

Pig. 25. "Chip cocoonsM of Pissodes approximatus showing, (a) one cell intact and (b) another opened to reveal the prepupa in• side. Note the excelsior-like covering viii

, of the cells 90

Fig. 26. Stem of a three-inch red pine infested with pissodes approximatus (pupal stage). 92

Fig. 27. Four-inch Scots pine stump infested with Pissodes approximatus and Hylobius pales (pupal stage). The lack of pupal cells above ground level is due to com• petition from bark beetles. 93

TABLES

TABLE I The duration of the immature stages of Hylobius radicis reared in an un- heated insectary during the summer- season. 33

TABLE II Mortality of immature Hylobius radicis calculated from populations on 60 red pines and 78 Scots pines and expressed as a percent of the initial egg popula• tion. 46

TABLE III Growth ratios for 20 Scots pines and 20 red pines heavily infested with Hylo• bius radicis 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 in an unheated in• 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 linear regression relationship. 82

TABLE VII The duration of the immature stages - of pissodes approximatus reared in 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, University of British

Columbia, for their guidance, encouragement and advice during this study. Much of the field work was made possible 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 in the employ of the Federal Government was granted by Dr. M. L. Prebble,

Chief, Porest Biology Division. I wish to thank Drs. R. M.

Belyea and M. L. Prebble for their criticisms of the manuscript.

The photographic work was done by Mr. D. C. Anderson, Bio- 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

in county forests and in Christmas tree plantations has

increased remarkably in southern Ontario as well as in the eastern United States. Several species of weevils are in• volved, sometimes attacking individually, but mostly in association with one another. The complex includes the pine root collar weevil, Hylobius radicis Buch., the pales weevil,

H. pales (Hbst.), the white pine weevil, Pissodes strobi

(Peck), the northern pine weevil, P. approximatus Hopk., and the strawberry root weevil, Brachyrhinus ovatus (Lee).

Although the importance of P. strobi as a forest pest has been known for over a century in North America, that of the

other weevils in the complex has not been fully appreciated until more recently. Two of them in fact, have only been

described as species since the turn of the century (P. app•

roximatus and H. radicis)•

It was the sudden rise from an unknown existence to

economic importance of H. radicis in southern Ontario in 2

1.954 that led to the present investigation. A. brief app•

raisal of the infestation in Simooe County early in 1955

showed that not only had H. radiois reached epidemic pro• portions in the area, but that two other weevils of the

complex (H. pales and P. approximatus) were also present

in sufficient numbers to contribute appreciably to the total damage of pine stands.

The purpose of this investigation has been to extend the present knowledge of the interrelationships between the three weevils and their host plants; of their economic

importance; and of the effect of the environment on their reproductive potential.

H. pales and P. approximatus both breed in dead or decadent pines and cause little or no damage as larvae. The adults, however, feed on the tender bark of coniferous seed• lings and may cause serious damage where outbreaks occur.

H. radicis, on the other hand, causes only slight damage by its adult feeding. However, its habit of attacking and breeding in the root collar of healthy pines, often causing the death of the tree, makes this weevil one of the more

serious forest pests in eastern North America.

Although the three weevils are native to North America, it is only during the last fifty years that they have been

considered as important forest pests. This change of their 5

economic importance, as a direct result of increase in nunri' bers, has been due largely to the actions of man by making available large quantities of breeding material either by clear cutting or by planting pure stands of pines. TAXONOMY

The genus Hylobius belongs to the tribe Hylobiini, sub-family Curculioninae, family Curculionidae. It contains about 50 species, five of which are native to North America;

H. -pales (Hbst.)„ H. congener (Delia Torre) (-confusus Kby.),

H. pinicola (Couper), H. radicis Buch,, and H. warreni Wood.

Although these five species are readily separated into two groups, the individuals within each group are very similar and may be easily confused. H. pales, H. congener^and H. ra• dicis^ on the average, are smaller than H. pinicola and H. warreni> and differ in general appearance from them. The shape of the femora and the presence or absence of teeth on it, as is indicated in the following key, are also important distinguishing characters of the two groups.

In 1934 Buchanan (16) described H. radicis as a new species and presented a synoptic key for H. pales, H. con• gener, and the new species H. radicis. These three weevils constituted all the North American species of the genus

Hylobius known at that time. Recently, Wood (125) in a re• view of the North American allies of the Eurasian species

Hylobius piceus (DeGeer), eliminated the genus Hypomolyx of Leconte by separating the single holarctic species in 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 is 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 virtually glabrous; anterior face of

at least the hind femur almost always

with a narrow, shallow, median groove

in about basal third; inner edge of fore

tibia of male with a fringe of white

hair, the length of some of the longer

hairs equal to width of tibia. 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 tibial 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 tibial uncus of male broad, parallel-sided, very broadly rounded at apex pales (Hbst.) Size larger, 9.4 to 13.0 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 tibial 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- ally; apical umbones of the elytra obscure or entirely undefined; meta- 7

•thoracic wings short, not extending

"beyond the posterior margin of first

visible abdominal sternum; male geni•

talia with apex of aedeagus blunt, the

anterodorsal margin of gonocoxites

conspicuously bisinuate, and lacking a

darkly pigmented median area within the

aedeagus warreni Wood

Rostrum slender, more than 2.9 times as long

as wide, not wider distally; apical urn-

bones of elytra prominent; metathoracic

wings long extending well beyond elytral

apex; male genitalia with apex of aedeagus

acutely pointed, the anterodorsal margin

of the gonocoxites evenly rounded; and

a pigmented median triangular or Y-shaped

area within the aedeagus visible from the

ventral aspects pinicola (Couper)

The genus Pissodes belongs to the tribe pissodini,

sub-family Curculioninae, family Curculionidae. It is a

large and cosmopolitan genus with about 30 species in North

America alone (71). Several of the eastern North American

species are so similar morphologically, that it has been found impossible to separate them on this basis. Since the similarity between the species often extend to their bio• nomics as well, it is suggestive that perhaps the group is experiencing an active period of evolution and that several populations possibly exist, at the sub-specific level.

From personal communications with Dr. G. K. Manna1 2 and Dr. S. G. Smith it has been learned that a close inter• relationship exists among weevils of the genus Pissodes.

Manna has found that P. strobi (peek), P. engelmanni Hopk., and P. sitchensis Hopk. all possess 34 chromosomes, while p. affinis Rand., P. radiatae Hopk., and P. fasciatus Rand, all 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 less gradual change from

30 chromosomes in weevils collected in southern Ontario to

32 chromosomes in weevils collected along the north shore

of the Great Lakes, to 34 chromosomes in weevils collected in central 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 is of the opinion that there is no ground for separating this population into two species (P. approximatus in the south and P. canadensis in the north) as done by

Hopkins (71).

It has been learned at a late date that Manna and Smith have recently published their findings 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 investigations of H. radicis, H. pales, and P. approximatus were carried out in Simcoe County in southern

Ontario, during the 1955, 1956, and 1957 growing seasons.

Field observations were made in 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. sylvestris L., and in nursery seedling beds at Angus and Midhurst, Ont. The laboratory observations were conducted at a field station at Angus, Ont. in the summer, and at the University of British Columbia and the

Porest Insect Laboratory at Sault Ste. Marie, Ont. during the winter.

Study of Insect Biologiest

In investigating the seasonal history and habits of the weevil complex, insect populations were kept under observation both in natural breeding material in the field and in cages in the insectary. The weevils reared in the insectary consisted of the progeny of twelve pairs (male and female) of young H. radicis; twelve pairs of young H. pales.; and twelve pairs of young p. approximatus. Each pair was kept separately in glass vials and permitted to feed and oviposit for two growing seasons on sections of pine 11

branches (four inches long and ^ inch in diameter), placed in the vials. Since the females sometimes dropped their eggs away from the pine material, the glass vials were placed with their open ends down on a wire screen so that the loose eggs fell through the screen onto a watch glass placed under• neath. Fresh pine branches were added to the vials daily, while the branches of the previous day were carefully peeled and examined for eggs. The twelve H. radicis females laid

380 eggs during the two summers, but only 84 were reared to the adult stage. The H. pales females laid 556 eggs, of which

73 were reared to adults, and the twelve P approximatus females, laid 522 eggs, of which 42 were reared to adults.

A special technique was devised for rearing the weevils.

This consisted of rearing the insect from the egg to the adult stage under glass, on fresh inner bark of Scots pine removed from the tree. The newly hatched larva was placed in a. small groove made on the cambial surface of the bark which was then pressed tightly against the bottom of a petri dish by filling the dish with sand and applying pressure on the cover with rubber bands (Pig. 1). The cover of the petri dish was lined with a "Kleenex" tissue 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 squirting about 1 cc. of water each day 12

Fig. 1. Method of rearing pine weevils in the insectary from the egg to the adult stage showing, (a) pouring the sand over the inner bark and screen; (b) a sectional view of the rearing unit. 13

between the edges of the petri dishes onto the "Kleenex" tissue.

During the prepupal stage, the larvae had a tendency to bore through the bark and disappear into the sand. In order to prevent this, a circular piece of galvanized wire screen wags cut to fit snugly inside the petri dish and placed over the bark before the sand was added. The screen disc, although preventing the prepupa from, entering the sand, did not interfere with the uniform pressure of the sand on the bark.

This rearing method permitted continuous observations

of larval and pupal development and the periodic measurment

of body size and extent of larval feeding (Pig. 2). It was possible to keep the inner bark green and free from fungus

contamination for more than two weeks by using sterilized

sand and glassware, and by keeping to a minimum the time

that the cambial surface of the inner bark was exposed to

the air during preparations. In rearing the weevils some

larvae were transferred to fresh bark after each moult,

while others were transferred after two moults, thus per•

mitting more accurate measurments of the feeding damage

by each instar. After the last instar larvae had constructed

pupal chambers, they were left undisturbed until the adults

were formed. Pig. 2. Larvae of Hylobius radicis in rearing,

(a) Feeding larva, (b) Prepupa in pupal cell.

Eighty-four H. radicis, 73 H. pales and 42 P. appro• ximatus were reared in this manner from egg to adult. The larvae thrived on the inner bark and their development corresponded very closely to that of free populations in the field. Although mortality of reared larvae was as high as 50fo during the early stages of experimentation, the tech• nique was eventually improved to the point where less than

5f<> of the larvae were lost.

Most of the data on the seasonal history of H. pales were obtained from white pine trees, the preferred host, one of which was felled and set up as trap logs near its stump every two weeks during five months of the 1956 grow• ing season. The trees, which were between 4 and 5 inches in diameter and formed part of a dense stand, were cut in

3-foot sections and placed horizontally on the ground. The

logs and roots of each tree were sampled and weevil develop• ment was recorded weekly until pupae began to form under the bark. At this time the stump and main root system were ex•

cavated and placed in outdoor screen cages. About 6 inches

of soil was kept over the stumps to prevent desiccation, pine bark freshly removed from trees was used in the cages as, traps for the emerging adults which were collected daily.

None of the logs set up in the field were successfully in• fested by the weevil, and they were discarded.

Ten Scots pine trees were used in a similar fashion to study the seasonal history and habits of P„approximatus.

The feeding habits of H. -pales were studied on natural

regeneration in the study plantations and on potted plants distributed in a grid pattern in a two-acre area cut over the previous fall in which the stumps were infested with

H. pales. Equal numbers (six of each species) of four-year-

old white pine, red pine, Austrian pine, P. nigra Am., and

Scots pine plants were set out. The feeding damage were ob•

served and tagged at weekly intervals.

Measurment of Damages

The effect of radicis 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 soil within each cage was sprayed thoroughly with ethylene dichloride, a fumigant, in order to kill 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

Fig. 3. Caged pine trees used in studying the bionomics of Hylobius radicis.

for damage and weevil population at the root collar.

The effect of H. radicis 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 infested with the weevil since 1950, 10 white pines, 20 red pines, and 20 Scots pines were cut and their annual height and radial increments measured for the period 1945 to 1955.

Since only the white pines in the stand were not infested 18

with the weevil, their measurements were used as an indication of normal growth over the ten year period considered and as a check on the growth of the two other heavily infested species. The trees were all cut in June and early July 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 collars of ten heavily infested Scots pines and ten red pines that had recently been killed by H. radicis« it was possible to de• termine the first year each tree was attacked and, roughly, the progress made by the weevils until the death of the tree.

During the 1955, 1956, and 1957 growing seasons, 78

Scots, pines and 60 red pines infested with Hi radicis were examined in order to determine the extent of damage, the number and distribution of the different stages in the vici• nity of the root collar, and to determine the cause and extent of mortality within each stage as the season pro• gressed. 19

HYLOBIUS RADICIS BUCH.

Hylobius radicis Buchanan (16)

BIOLOGY: Felt (30, 31, 32, 33, 34, 37 (pales), 39,

40, 41, 42, 43, 45, 47), York (126 (pales)),

Glasgow (60, 61), plumb (90, 91, 92), Felt

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).

History:

H. radicis was described in 1934 by Buchanan (16) foll• owing several reports by Felt (30, 31, 32, 33, 34, 37) and

York (126) describing a new type of weevil damage on Scots pine, red pine, and pitch pine, P. rigida Mill., in the State of New York, which they believed was caused by the pales weevil. From 1934 to 1942, several short reports on the hosts, distribution and damage caused by H. radicis were made by

Felt (37, 41, 43, 47), Felt 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 life history, habits, economic 20

importance, and control of the species in the New England

States, stating that the weevil was a serious pest of Scots pine, Austrian pine, and its variety Corsican pine. They also noted that heavy infestations were observed only where the trees were growing in light sandy soils as reported earlier by Pelt and Bromley (49). Schaffner and Mclntyre stated further that infestations were also observed in jack pine,

Mugho pine» P. mugho Turra., pitch pine, red pine, and eastern white pine, but that serious injury occured to these species only where they were growing near infested Scots or Austrian pines. In 1950 Shenefelt (111) presented a paper on the chemical control of the weevil in Wisconsin.

In Canada, the first record of H. radicis was made by iallaeje (120) in 1954, who reported up to 25$ mortality in

Scots and red pine plantations infested by the weevil in southern Ontario. The following year 1/latson (123) presented a morphological description of the full grown larva of the weevil, and Prentice (94) reported damage to red pine and jack pine in Manitoba, that later proved to be an infestation of this species. In 1956 Pinnegan (52) discussed briefly the damage caused by H. radicis in association with Hj. pales and P. approximatus in southern Ontario. The origin of the weevil in Manitoba was briefly discussed by l/parren (121) in 1956. 21

Description of Life History Stages;

ADULT: The adult H. radicis is robust, measuring from

9.4 to 13.0 mm. in length and from 3.7 to 5.2 mm. in width

(Fig. 4,, d). The weevil is dark brown and is marked irregu• larly on the thorax and elytra with spots of cream coloured, scale-like hairs. The beak is stout and about as long as the prothorax, with the antennae attached slightly in front of the middle. It resembles closely H. pales, and although

Buchanan (16) gives a considerable list 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, in comparison with pales, are the larger size, the lack of scaly spot on forehead and the spotted, rather than barred elytra." Since all of these characters intergrade, it is very difficult to separate a large percentage of the weevil population. In the field, the best macroscopic characters that can be used to separate the two species with some degree of accuracy, is the larger body size and spotted elytra of H. radicis as contrasted with the smaller body size and barred elytra of H. pales (fig. 5).

The male H. radicis is about 1.5 mm., shorter than the female. It also differs from the female in three main charac• ters; first, the uncus of the hind tibia is stouter and distinctly flattened in the male, while that of the female Fig. 4. Hylobius radicis. (a) Egg x24; (b) Larva x6

(e) Pupa in earthen cell x6; (d) Adult x6. 23

Fig. 5. Dorsal view of (a) Hylobius radicis and (b) H.

•pales, showing the scattered spots on the elytra of H. radicis

in contrast to the barred pattern on the elytra of H. pales. 24

is conical (Fig. 6 a, c); second, the first and second ab• dominal sternites, of the male are more or less concave along the median line, while in the female they are convex

(Fig. 6 d); third, in the male the middle part of the fifth abdominal sternite exhibits a circular impression distingui• shing it from the lateral parts (Fig. 6 d).

EGGs The egg is ellipsoidal and measures 1.92 ± 0.10 mm. in length and 1.15 ± 0.05 mm. in diameter (Fig. 4a). It is opaque and dull creamy white in colour.

LARVA* The larva is typically curculionid in form (Fig.

4 b). Ihen fully grown it is about 15 nun. in length with a legless white body, dark-brown head and black mandibles.

The width of the head capsules of the 84 larvae reared in the insectary were measured after each moult from the egg to the pupa. Fig. 7 illustrates the distribution of these measurments separated by sex, as they developed through each instar. Seven larvae (all females) pupated after a minimum of five instars; 45 (23"males- and: 22. females) required six instars; and the remaining 52 (23 males and 9 females), seven instars before pupating.

Although there is a large overlap between the size of head capsules of males and females in each instar, the mean value for the females is consistently larger than that of Fig. 6. (a) Hind tibial uncus of Hylobius radicis males; (b) Hind tibial uncus of H. pales males; (c)

Hind tibial uncus of H. radicis and H. pales females and (d) Abdominal impressions found on H. radicis and

H. pales males.

27

100 1.50 2.00 2.50 HEAD CAPSULE WIDTH IN MM.

Fig. 7. Distribution of head capsule measurmehts of 84

Hylobius radicis larvae reared in the insectary from the egg to the adult. The cross-hatched areas represent the overlap between adjacent instars.

the males in corresponding instars. This trend continues to the adult and accounts for the larger average size of the females in the adult population.

While the head capsule measurments of the reared larvae fall into a distinct class for each of the first six instars, the measurments of 476 larvae collected in the field during two growing seasons give little or no indication 28

1.50 2.00 HEAD CAPSULE WIDTH IN MM.

Pig. 8. Distribution of head capsule measurments of

Hylobius radicis, representing (a) 476 larvae collected in the field; (b) 84 larvae reared in the insectary.

of the number of instars present. The distribution of these measurments is shown in pig. 8. The difficulty experienced in finding the first and second instar larvae in the bark is largely responsible for the small number of these indi• viduals in the sample, while the relatively larger prepupal stage is responsible for the large number of prepupae col• lected. The lack of resolution of head capsule measurments of larvae collected in the field into classes according to instars is to be expected where such a large number of in• stars is present. The influence of the environment on the growth of the weevils, particularly those that overwinter in the larval stage, is great, and it is only under rigidly controlled rearing conditions that sufficiently uniform larval development occurs to reveal the basic growth pattern,

PUPAs The pupa is completely white when first formed

(Pig, 4 c). The eyes and mandibles turn black about the eight or ninth day, and the rostrum, prothorax, and legs darken to medium brown about two weeks after pupation.

Distribution and Hosts?

Since 1934, H. radicis has been reported in Minnesota,

Wisconsin, Pennsylvania, Massachusetts, Connecticut, New

York, and Virginia in the United States, and in Manitoba and Ontario in Canada (16, 32, 69, 94, 109, HI, 120). In

Ontario the weevil has been found throughout Simcoe County and in two other widely separated areas - Sault Ste. Marie 30

and Petawawa.

Schaffner and Mclntyre (109) report the following

trees as host plants?

Pinus sylvestris L. Scots pine. " nigra Am. Austrian pine. " banksiana Lamb. Jack pine. mugho Turra. Mugho pine. rigida Mill. Pitch pine. resinosa Ait. Red pine. strobus L. Eastern white pine.

In southern Ontario, it was found infesting Scots pine,

red pine, Austrian pine, Mugho pine, and jack- pine, but was

never found on white pine. Trees of all ages with a root

collar in excess of 1-^- inches may be attacked.

Seasonal History?

In southern Ontario, H. radicis overwinters in the

larval, pupal, and adult stages. Young overwintered adults

oviposit from early May until September, and then usually

overwinter again to lay eggs during a second season (Pig. 9)»

A few of the larvae arising from eggs laid in early May

complete their development in time to pupate in September

and overwinter as adults. Prom a total of 84 eggs reared in

the insectary, 11 developed to adults in one season (before

the end of September), while the remainder overwintered as

larvae to pupate in late June and early July of the next 31

STAGE WIN. MAY JUNE|JULY AUG. SEPT. OCT. 1 WIN. MAY JUNE JULY AUG. SEPT. OCT. WIN. ADULT m EGG P

-1B"~ - s LARVA 1 m PUPA 1 "

n • ' — ADULT I —:

EGG H I 11 LARVA III 1 1 ^.„„:„':„,.,:.:':!:J:^,.:. PUPA HI; ADULT n ft

Pig. 9. Seasonal history of Hylobius radicis in southern

Ontario.

year. Schaffner and Mclntyre (109) report a two-year life

cycle for the species in the New England States, but do

not mention the possibility of part of the population having

a one-year life cycle.

The earliest egg found in the field was on May 2,

1955, while in the insectary oviposition took place as

early as mid-April in 1958. The number of eggs laid varies

greatly between females. Whereas some females lay 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 first 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 field the larvae overwinter in all but the first 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 larval population pupates over a short period in early July. During the latter part of the summer,

TABLE I

The duration of the immature stages of Hylobius. radicis reared in an unheated insectary during the summer season

Stage ' Time (days)

Egg : 14.5 ± 1.2

1st instar j 8.6 ± 1.0

2nd instar • 8.3 ± 1.9

3rd instar : 9.5 ± 1.3

4th instar : 11.8 ± 1.5

5th instar (Prepupa) '. 27.5 ± 6.2

5th instar ! 17.0 ± 4.0

6th instar (Prepupa) I 31.0 ±6.8

6th instar \ 24.1 ± 4.4

7th instar (Prepupa) : 28.2 ± 5.1

Pupa : 19.8 ± 4.6

in August and September, a few pupae can be found, but these

have arisen from eggs laid early in the spring of the same

year and not from overwintered larvae. The earliest pupa found, in the field was on June 20, 1957.

Habits?

The adults usually overwinter in crevices in the outer bark of the stem of living pine trees, at or slightly below ground level, but a small number overwinter in the duff at the base of the trees. In southern Ontario, the overwintered adults become active during the latter part of April and apparently spend most of their lives in and around the root

collar of the host tree, mating and ovipositing from early

May to mid-September. The eggs are often laid in the soil as far as. two inches from the tree, but usually they are placed in feeding wounds made by the adults in the inner bark of the root collar.

T/1/hen the eggs hatch, the young larvae are very active and begin searching for food immediately. If the eggs are

laid close to the cambium of the tree, the larvae experience

no difficulty in establishing themselves. When a tree is

first attacked, the young larvae feed mostly in the inner

bark, although the surface of the wood is also slightly

scarred. The feeding is confined to isolated areas around

the root collar that usually become elliptical in shape with

the long axis running parallel to the grain of the wood.

They increase in size as the larvae develop and in large

trees are usually re-infested by the larvae of succeeding Fig. 10. Section through the root collar of a six-inch

Scots pine showing typical wounds caused by Hylobius radicis larvae. This tree had been infested for at least thirteen years.

generations. Thus the trunk at the root collar becomes fluted, since the undamaged cambium grows beyond the injury on either side of the wound (Fig. 10). Eventually, as the infestation increases, the tree becomes completely girdled 36

Fig. 11. Hylobius radicis damage "to the root collar of

Scots pine, (a) Root collar of infested tree with the pitch- infiltrated soil partly removed to show a larva in the outer bark; (b) Stump of infested tree with soil completely removed to show swelling at the root collar due to larval damage;

(c) Stump of infested tree with bark removed from the root collar to show the extent of damage to the wood. and death follows (Pig. 11 o). If the tree is healthy and

vigorous, it responds to the larval damage by producing

copius quantities of resinous sap at the site of the injury

so that large pockets of gum are formed. Advanced larvae are

apparently well adapted to living in this environment, for

they are often found completely immersed in the sticky sub•

stance. It apparently becomes necessary, however, to relieve

the sap pressure periodically, and larvae accomplish this

by digging circuitous tunnels several inches in length into the soil, thus leading some of the sap away from the injured area. Consequently, in a heavily infested tree the soil surrounding the root collar soon becomes soaked with resin for a distance of up to two or' three inches from the tree

(Pig. 11 a). TSBien the larvae are fully grown they make a final journey into the soil up to two inches from the tree and there construct pupal cells in which they pupate (Pig.

4 c). Occasionally the cell is constructed in the gum-soaked

outer bark. Pig. 12 shows the distribution of larvae and pupae found in the soil surrounding the root collars of

infested trees. The pupal cell is usually made with its

long axis vertical, or slightly inclined to the vertical.

Its depth varies from soil level to about ten inches below

the surface. The larva covers the inside of the cell with a cement-like substance (possibly resin from the tree), Fig. 12. Distribution of Hylobius radicis larvae and pupae in the soil around the root collar of infested

Scots pines.

10

XL n.,, n a AUG.

TIME OF YEAR

Pig. 13. Emergence of Hylobius radicis adults from twenty trees during the summer of 1955.

which binds the grains of sand into a hard shell-like structure. It then remains inactive for about one week before pupating.

The newly formed callow adults remain inactive in their pupal cells from one to two weeks before emerging from the soil. In June, 1955> twenty heavily infested stumps from three to four inches in diameter were dug up, each with a one-foot ball of earth around the root collar, and placed in cages for emergence observations. Fresh bark was placed in each cage weekly during the emergence period to attract the weevils as they emerged from the soil and daily collections were made from the bark. Fig. 13 shows 41

the emergence pattern of the 96 weevils collected - 46 of which were males and 50 females.

The young adults begin feeding almost immediately after emerging from the soil. They feed on the inner bark of the trunk in the vicinity of the root collar and occasionally, at night, on the tender bark of twigs and small branches of healthy trees. However, the adult population in the field is never sufficiently large to cause serious feeding damage.

The feeding damage is quite conspicuous on branches, appear• ing as small open pits about in diameter that often coalesce to form larger wound areas, in a natural stand, the rate of spread of the weevil is not rapid since adults emerg• ing from the root collar of a living tree usually remain to continue and increase the infestation on that particular tree. However, in infested pine plantations, where heavy

cuts are made periodically, the weevils emerging from a stump

or dead tree must of necessity find new living material on which to feed and oviposit, producing a more rapid spread of the weevil than is otherwise experienced. This fact was established by setting out bark traps from early May until mid-September in both a heavily infested Scots pine stand and in a recently cut-over area where the infested stumps had been left in the ground. No weevils were found on the bark traps in the infested stand - indicating a lack of 42

migration - while a large number was collected from the bark

traps placed in the stump area.

Limiting Factors?

In southern Ontario, H. radicis is found in epidemic

numbers only in areas where exotic pines (mostly Scots and

Austrian pines), are grown extensively. The weevil will

attack open-grown Scots pine as heavily as Scots pine grown

in a dense stand. However it was never found on native pines,

even in dense stands, isolated from exotic pines. Where a

stand of pure red or jack pine grows adjacent to an infested

stand of Scots pine, only the marginal red and jack pines

become infested. In mixed stands of native and exotic species

on the other hand, all the trees are susceptible to infes•

tation.

While stand composition and density are apparently

critical factors limiting weevil population per tree on

native pines, they do not seem to be important to weevil

densities on exotic species. This is, probably due to physio•

logical differences in the two groups of pines.

Throughout the year the weevil population on Scots

pine was almost 50f0 higher than on red pine of similar size,

even where infestations were heavy and the two species grew

in close proximity to each other. Field observations showed 43

that adult females ovipositing on red pine laid as. .many eggs as those ovipositing on Scots pine, hut that the coefficient of destruction for the immature stages differed for popula• tions breeding on these two hosts» In both pines the greatest mortality occurred in the egg stage and during the establish• ment of the newly hatched larvae. In the insectary it was found that about 30$ of the eggs laid did not hatch. Apart from this initial loss, a large number of eggs are subjected to possible predation by mites and other soil scavengers, since approximately 25$ are deposited in the soil as far as three inches from the tree. It was not possible to determine accurately the extent of this hazard, but larval counts of first-instar larvae in the soil around the root collar of infested trees kept in cages indicated that in both red pine and Scots, pine about 20$ of the viable eggs were destroyed before they hatched. The viable eggs laid in niches in the inner bark of the root collar, on the other hand, are well protected by plant tissues and juices and suffer little or no mortality from predation.

The newly hatched larvae are active and may live up to four days without eating. Therefore, larvae emerging from eggs laid in the soil are usually able to reach living tissue of the near-by root collar before starving. It is while attempting to establish itself in the cambium of the 44

living tree that the larval population suffers its greatest mortality. The flow of sap from the freshly wounded root

collar is very pronounced and in Scots pine kills up to 60$

of the young larvae, while in red pine as much as 75$ of the larvae are killed at this time.

Once the larvae have succeeded in establishing them• selves in the living tissues of the root collar, they are we3Ll protected from the environment, since they are almost always completely surrounded by large quantities of sticky resin which acts as an excellent protection against predators and parasites. The larval stage is practically free from parasite attack. During the whole study period only two larvae collected in the field were found to be parasitized.

Three parasites emerged from these two larvae and were iden- v \V> tified as Coeloides sp_.

The pupa is well protected in the pupal chamber. The cell wall, although hard and cement-like, is not impervious to moisture, however, and when prolonged precipitation occurs during the pupal period, flooding may cause the death of the occupants. During the month of July, 1956, 4.42 inches of rain fell in the Angus area as compared with an average of

2.77 inches for the previous 45 years. The following week a check was made on the condition of the pupae in" the soil and it was found that about 15$ died from drowning. The small, pupal population that enters hibernation in the fall suffers heavy mortality due to low temperatures.

In November, 1957, about 85$ of the pupae were dead in their chambers, while in April of the following spring mortality had risen to over 95$.

The adults spend nearly their whole lives in the duff surrounding the root collar of pines on which they feed and oviposit. In this environment they are relatively free from the effect of climate and attack by predators. Death in this stage occurs mostly during the overwintering period. Out of an initial population of 67 young adults reared from pupae during the summer of 1955, H» or 16$, died during the first winter and 41, or 61$, during the second winter. These adults were overwintered in an unheated insectary in cages contain• ing six inches of sterilized sawdust.

During the summer of 1956 after adult emergence from

infested stumps kept in cages had ceased, the soil surrounding the stumps wqs examined for adults that had failed to emerge from, their pupal chambers. It was found that 21$ of the new adults, had died in their cells and were infested with a green

external fungus and a white internal fungus. The green fungus was identified as a saprophytic Benicillium sp. but efforts ^ to grow the white fungus on either artificial media or living insects in the laboratory failed and identification was not possible.

The mortality of the immature stages of H. radicis is summarized in Table II for both red and Scots pines.

TABLE II

Mortality of immature Hylobius radicis, calcu• lated from populations on 60 red pines and 78 Scots pines and expressed as a percent of the initial egg population.

Mortality (percent) Host ; I Egg '' [ Larva Pupa

red pine : 41.8 \ 45.0 \ 2.0

Scots " 1 43.2 i\ 35.4 1 2.8

» *

Effect on the Tree?

H. radicis will attack healthy trees from li- inches in diameter at stump height (6 inches above ground), to mature trees measuring as much as two feet in diameter at breaat height. Scots pines measuring less than 4" dbh. are normally killed after three or four years of heavy infesta• tion, while red and jack pines can withstand the attack for one or two years longer. Pines that are larger than 4" dbh. when first attacked are seldom completely girdled, although their root collars may be seriously weakened. SIGNS AND SYMPTOMSs The first external symptom of the tree to weevil attack consists of sap escaping from the wounded root collar into the surrounding soil, producing a compactLlayer of pitch-infiltrated soil often two or three inches in thickness over the whole damaged area (Pig; 11 a).

Under the resin-soaked soil the outer bark of the stem is usually well preserved, although often separated from the sound wood by as much as one inch of gummy semi-hardened resin mixed with larval frass. It is in this layer that most of the larval population is found; In a heavily infested tree, removal of the outer bark and the gummy resin around the root collar reveals a greatly reduced stem with only a small amount of cambium bridging the damaged area (Pig. 11 c)

The tree may remain alive and vigorous under these conditions for several years. The large quantity of sap covering the wound creates a moist septic condition favourable to the plant; However, trees that are open-grown or at the edge of stands are very susceptible to windthrow and snowbreak and usually lean heavily in the direction of the prevailing winds

(Pig. 14). Although windthrow has not yet occurred exten• sively in dense stands in southern Ontario, it is conceiv• able that should exceptionally strong winds occur, this type of damage would be commonplace, for trees measuring 6" dbh. heavily infested with H. radicis for five to ten years can usually be pushed over by two men without great difficulty. Fig. 14. Hylobius radicis damage, (a) A heavily infested twenty-year-old Scots pine plantation; (b) Two infested trees broken at the root collar and blown over by wind. 49

When the tree is completely girdled, there is a rela• tively short period during which the colour of the foliage changes from green to a pale yellow followed by a red and then brown colouration;

EFFECT ON GROWTHS The effect of H. radicis damage on the growth of pines was studied by measuring the annual height and radial increments of twenty-year-old Scots, red, and white pines for the period 1945 to 1955» An average of 10.1 and 9»7 immature weevils were found on the Scots and red pines respectively, showing that the trees were heavily attacked, but none of the white pines were infested. Twenty

Scots and 20 red pines, heavily infested since 1950, and

10 non-infested white pines were measured. Fig. 15 shows the average growth of these trees, both in height and radially.

When the growth curves of the Soots and red pines are examined individually, there is no indication of a reduction in growth from 1950 to 1955» except for the height increment of Scots pine which drops slightly. The apparent lack of effect on these two pines by weevil attack was further empha• sized by the normal length and colour of their needles and the general healthy appearance of the crowns.

Blais (4) states that the first year of growth suppres• sion of balsam fir and white spruce, Picea glauca (Moench)

Voss, heavily defoliated by the spruce budworm, Choristoneura Fig. 15. Growth curves of 20 reel pines and 20 Scots pines, heavily infested with Hylobius radicis, and 10 healthy white pines growing in a mixed stand. The trees were all 22 years old. DATE (YEARS) fumif erarta Clem.,, several years in succession, can be indi• cated by growth ratios obtained by dividing the average annual increment of the affected species by the average annual growth increment of non-infested species growing in the same area^ He considers, the apparent first year of growth supression to be the one showing a growth ratio less than that of any of the preceeding years, followed by a series of declining ratios. Table III shows the annual growth ratios

TABLE III

Growth ratios for 20 Scots pines and 20 red pines heavily infested with Hylobius radicis.

Scots pine Red pine' Year Radial [ Height | Radial Height ' . growth : growth growth ! growth

1

1945 1,55 : 1.44 '; 0.75 '', 0.95 [? ' 1946 1.04 ' 0.85 \ 1,52 1947 | 1.07 ' 1.89 ' 0.98 ' 1.25

1,35 1.08 1948 .t 1.26 \ 1.50 ! 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 in this manner. It can be seen fnom the ratios that there is an apparent reduction in the growth of the two infested species from 1951 to 1955. then Blais1 criterion is applied to the data in Table III, the first year of suppression for Scots pine is apparently

1951 for height growth and 1952 for radial growth, This is true also for red pine if the small ratios for height growth in 1946 and radial growth in 1945 are ignored. The growth ratios for the year 1954 all show slight increases suggesting a recovery of the affected species from weevil attack during that year. It should be kept in mind, however, that Blais* analysis of the effect of C. fumiferana on the growth of balsam fir 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 in 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 in• fested pines, it was. found that Scots pines attacked at the age of four or five years were killed about three or four years later, while trees attacked when 10 to 15 years of Fig. 16. Hylobius radicis damage, showing alternate rows of living infested red pines and dead Scots pines.

age died after six to eight years of infestation. In general red pines remained alive about three years longer than Scots pines in the same area. In stands where Scots pines and red pines are planted in alternate rows this is very stricking, for the early death of the Scots pine creates a contrast with the apparently healthy red pines as shown in Fig. 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).

assimilis Roelofs (99). pissodes macellus Germar (58), Leconte (75).

BIOLOGY: Harris (64, 65), Pitch (53), Le Baron (74),

Dodge (23), Smith (112), Packard (79, 80, 81),

Thomas (119), Saunders (100, 101), Hopkins

(70), Pelt (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),

Britton (12), Wells (124), Anon (1), Britton

and Zappe (14), Craighead (19, 20), Dietrich

(21, 22), Knull (72), York (126), Glasgow (60,

61), Schaffner (103, 107), Pelt and Bromley

(49), Friend (54), Lyle (77), Robinson (97,

98), Savley (102), Bourne (8), Prico (95),

Conklin (18), Eddy (26), Hetrick (67), Friend

and Chamberlin (57), Beal and McClintick (2),

Bess (3), Sentell (110), Holt (69), Ebel and

Speers (25), Speers (lt-4, 115), Thatcher (118). 57

History;

H. pales was described in 1797 by Herbst (66) and placed in the genus Curculio. In 1834, Boheman (6) transferred it 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 briefly by Pelt (27), Pitch

(53), Harris (64, 65), Packard (79, 80, 81), and Thomas (119).

It was not until Carter (17) in 1916 and Peirson (82) in 1921 pointed out its role in limiting white pine regeneration in cut-over areas by feeding on the tender bark of seedlings, that the importance of the insect was fully realized. Carter

(17) reported that H. pales was a very important factor in limiting the reproduction of conifers in and around cut-over areas of white pine in 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 killed during the first two years following clear cutting of white pine. He concluded that it was unwise to plant cut-over pine lands during the first two seasons after cutting operations, because the weevil population remained high in the area for at least that length of time. He warned further, that in planting pasture land with conifers large pines in the area should not be cut before the planting because the seedlings in the 58

vicinity of the stumps would he subjected to heavy feeding by the weevil and the resulting loss would produce open areas in the plantation. He maintained that H. pales damage to conifer regeneration would likely be heavier in areas where the shelterwood method of cutting was used, since the final cutting after the regeneration had become established would produce breeding material for a large population of weevils.

He stated that injury to pine reproduction could also be ex• pected where strip cutting was practiced, especially where the strips progressed from leeward to windward, since weevil damage was almost invariably found as far as 100 yards from the edge of the old stand.

peirson»s (82) paper in 1921 presented the life history and control of H. pales for the State of Massachussets. He discussed at some length the history, distribution and host plants,, seasonal history, habits, and control of the weevil;

More recent papers by Beal and McClintick (2), Bess (3),

Savely (1020» Sentell (110), and Wells (124) have pointed out the continued importance of the weevil as a forest pest and have shown that it is found over most of the United^

States east of the Mississippi and north of Florida, and from Nova Scotia to Manitoba in Canada; In reporting their observations on H. pales injury to white pine plantings in

Few. England in 1942, Friend and Chamberlin (57) stated that 59

in addition to the size and density of the young trees, the number of stumps present and the proximity of the trees to them is important, and that the amount of damage in an area is dependent to some extent on the presence or absence of new areas in the vicinity attractive to the weevil. If new

areas did not materialize!,~f the adults usually remained in 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 in 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 in the field was promising and deserved further study.

Speers (114, 115) also discussed controls for the weevil with dips and sprays.

Description of Life History Stages;

ADULT $ The adult H. pales is robust, measuring from 5.8 to 11.3 nim. in length and from 2.1 to 4.5 mm. in width (Pig.

17)% and closely resembles H. radicis. The prothorax and

elytra are usually conspicuously marked with spots of cream

coloured scale-like hairs. In most individuals the elytral

spots are arranged in 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 in bars (Pig. 5a).

As stated previously, no difficulty is experienced in 61

separating the males., of the two species by the shape of the hind tibial uncus (Pig. 6 a, b). The females, however, are very similar and unless the elytral markings, average size, and amount of scales present on the front of the head are typical for each species, it is not possible to separate them with certainty. The three secondary sex characters des• cribed for H. radicis also apply to H. pales (Pig. 6).

EGG? The egg is ellipsoidal and measures 1.10 ± 0^07 mm. in length and 0.68 ± 0.04 mm. in diameter. It is opaque and dull creamy white in colour. It is only in this stage that

H. pales, and H. radicis can be completely separated, since the eggs of H. radicis are almost twice as large as those of H. pales.

LARVA$ The larva is typically curculionid in form and when fully grown measures about 12. mm. in length. It has a legless white body, dark brown head, and black mandibles.

At present it is impossible to separate, morphologically, the larvae of H. pales from those of H. radicis, except for the first instar H, pales larvae, which are smaller than the smallest H. radicis larvae, and the largest H. radicis larvae

(seventh instar) which are larger than the maximum size attained by H. pales, larvae^

Out of 73 larvae reared in the insectary from egg to ui 30 -

:.50 HEAD CAPSULE WIDTH IN MM.

Pig. 18. Distribution of head capsule measurments of 73

Hylobius pales larvae reared in the insectary from the egg to the adult. The black area represents the measurments of the fifth instar larvae that continued development to a sixth instar before pupating.

adult, 33 were males and 40 were females. Pig. 18 illustrate the distribution of measurments of head capsule widths of these larvae separated by sex as they developed through each instar. It can be seen from the graph that most of the

larvae pupated after five instars, but that 16 males and 18 63

females required six instars before pupating.

Simple calculations comparing the ratio of the means of the head capsule widths of successive instars show that this ratio is relatively constant for the first five instars of both males and females, but that between the fifth and sixth instars it 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

Observed \ Calculated measurments \ widths Sex : Instar- | widths [ ratios | (Dyar's Rule)

; I 0.72 : t II 0.68 ' . 0.68 j 0.73 :.. Male | III ! 0.94 ; 0.94 ; 0.69 i IV - 1.37 1 1.31 '. 0.76 Y ; 1.82 ; l.8l ! ; 0.83 ! VI i 2.18 1 2.51

I : 0.51 ! 0.68 II ] 0.75 ; 0.72 0.71 Female < III ! 1.06 \ 1.01 ! 0.69 IV 1 [ 1.52 ! 1.42 • 0.76 ' V ! 2.00 I 2.00 ! 0.82 ! VI 2.43 ! 2.81 • 64

the mean of the sixth instar is closer to the mean of the fifth instar, for each sex, than is indicated by Dyar's Rule.

The cause of the increase in the ratio becomes evident when the larvae of the sixth instar are traced back to their proper positions in the fifth instar* The shaded areas under the fifth instar in Pig. 18 represents these larvae and they are seen to be the smaller individuals of that instar. This means that the sixth instar larvae are not representative of the fifth instar in head capsule width and consequently have a mean width less than is predicted by Dyar's rule.

It is of further interest that since the size of the adult is closely related to the size of the prepupa, as shown in

Pig. 19, the smaller usually less vigorous larvae, by con• tinuing their development to a sixth instar before pupating, ultimately produce the larger adults in the weevil popula• tion.

PUPA? The pupa is completely white when first formed, but the eyes and mandibles turn black and the rostrum, pro- thorax, and legs darken to medium brown before changing to the adult.

Distribution and Hosts?

Peirson (82) stated that the distribution 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.

Pig. 19. Relationship between the head capsule size of prepupae and adults of Hylobius pales. The regression line

Y = 0.413X + 0.889 has been fitted to the data.

was general throughout the eastern half of the United States and in southeastern Canada. He pointed out that since this range was greater than the range of the weevil's favorite food plant, white pine, other trees must necessarily be used as food and breeding material. This was later shown to be true by several workers (2, 21, 25, 97, 102, 110) who reported the weevil feeding on southern pines and other conifers in northern Florida, Alabama, and Mississippi

During the past 50 years the following trees have been reported as adult food plants (2, 17, 57, 82, 124) s

Pinus strobus L. Eastern white pine. " rigida Mill. Pitch pine. M resinosa Ait. Red pine. ponderosa Laws. Ponderosa pine. " sylvestris L. Scots pine. " taeda L. Loblolly pine. » echinata Mill. Shortleaf pine. " palustris Mill. Longleaf pine. " virginiana Mill. Virginia pine. " mugho Turra. Mugho pine. M cembroides Zucc, Cembra-pine• Larix laricina (Du Roi) K. Koch Tamarack. » decidua Mill. European larch. Picea rubens Sarg. Red spruce. " abies (L.) Karst. Norway spruce. Abies balsamea (L.) Mill. Balsam fir. Tsuga canadensis. (L.) Carr. Eastern hemlock. Pseudotsuga menziesii (Mirbel) Franco Douglas fir. Juniperus communis L. Dwarf juniper. " virginiana L. Red juniper. Cupressus arizoniea Green. Arizona cypress. Cedrus deodara (Roxb.) Loud. Deodar cedar. Betula. populifolia Marsh. Wire birch. Fraxinus americana L. White ash.

However, Carter (17), Peirson (82), and Friend and Cham- berlin (57) agree that white pine is the preferred food plant. In southern Ontario the weevil has been found feeding on white pine, red pine, jack pine, Austrian pine, Scots pine and tamarack. Although feeding occurs on the branches of large trees, the trees suffer little or no damage after they have reached a height of about ten feet. 67

It has not been clearly stated, however, in what plants the weevil breeds. Several authors refer to pines and spruces as suitable breeding material (5» 57, 82, 124), but only white pine, pitch pine, ponderosa pine, mugho pine, and cembra pine have been named specifically 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 well 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 size.

Seasonal History?

According to Peirson (82), H. pales adults emerge.from hibernation about mid-May in Massachusetts and feed until about mid-June, at which time they migrate to an area where there is suitable breeding material. He indicated that ovi- position begins about July 1, that the resulting larvae pupate about September 1 to emerge as adults about October

I, and that they feed for twp or three weeks before entering hibernation, thus completing one generation per year. Although

Peirson does not elaborate the point, he concluded, on the basis of larvae having been found as late as October 8, that some individuals undoubtedly pass the winter in the larval or pupal stage in stumps or logs. Beal and McClintick (2) 68

Pig. 20. Seasonal history of Hylobius pales in southern

Ontario.

questioned Peirson's description of the seasonal history, and stated that in North Carolina there is "one complete generation and a partial second overlapping generation annually". In southern Ontario, H. pales overwinters in both the adult and larval stages (Pig. 20). Approximately

70$ of the summer larvae pupate and emerge as adults from late-August to mid-October to overwinter after a short feed• ing period. The remaining 30$ overwinter in the larval stage. 69

Head capsule measurments of 27 overwintering larvae collected late in November indicated that they overwinter only in the fifth and sixth instars. These larvae continue development during the following spring and emerge as. adults from about mid-June to August 1. Only a few eggs are laid by these early adults during the current summer. In the fall the early adults merge with the main adult population to over• winter in the soil, usually at the base of young plants on which they were feeding. The overwintered adults emerge from hibernation in late April and early May and feed for about two months before ovipositing. The first egg laid in the insectary in 1958 was on June 12; the general oviposition period lasted until the end of July, although one female laid three viable eggs on August 30 after being inactive for over four weeks.

Rearing experiments showed that adult weevils are long- lived; about 35$ overwintering twice, the females ovipositing during two successive growing seasons. The females lay about

30 eggs, or 60$ of their total quota, during the summer following the first overwintering period as adults, and about

18, or 40$, during the second summer.

In 1957 the first summer larva was found in the field on July 6. The larval period lasts for about 47 days, followed by a pupal period of about 22 days. Table V shows the average duration of each of the instars for both f ive- and six-instar larvae, as well as for the egg and pupal stages, of weevils reared in an unheated insectary during the summer months. In southern Ontario the first pupa to \ appear in the field in 1957 was on August 26. The newly formed adults remain in their pupal cells about two weeks before emerging through the bark and soil. The peak of adult emergence is about the last week of September.

TABLE V

The duration of the immature stages of Hylobius -pales reared in an un• heated insectary during the summer season

Stage ! Time (days)

Egg 9.9 ± 1.3

1st instar j 5.3 ± 0.8

2nd instar j• 5.0 ± 0.8

3rd instar j\ 5.1 ± 0.7

4th instar s\ 6.5 * 1.0

5th instar (Prepupa) s• 20.8 ± 2.2

5th instar i .9.3 i 1.4

6th instar (Prepupa) j\ 21.3 ± 2.8

Pupa , 21.8 ± 1.3 Habits$

The adults overwinter in the duff and soil at the foot of the small tree or seedling on which it was feeding. They are often gregarious at this time of year and may be found in small groups usually under such objects as wood chips, small rocks, or the roots of trees. In southern Ontario, they become active in early May at which time they emerge from the soil and continue their feeding at night on the tender bark of seedlings and small branches of larger trees throughout the growing season and then enter the soil to overwinter again.

During th© egg laying season, the females enter the soil overlying the roots of fresh stumps and oviposit in niches chewed in the inner bark of the roots and the part

of the stump below ground level. The female lays her eggs erratically, sometimes laying two or three in one day, followed by several days of inactivity, during which time it feeds on healthy pines above ground^ The eggs are usually deposited singly, but sometimes two or'three are placed together in single niches chewed by the female.

The newly hatched larvae feed in" the cambial area of the roots or stump, scarring the wood more deeply than the

inner bark. The tunnels do not form a definite pattern in the lower part, of the stump, but wander without respect to 72

•the grain of the wood. In the roots, however, the tunnels always run with the grain, y/hen the larvae reach maturity they construct "chip cocoons" in the wood about V in depth and parallel to the grain. These cells may be found in the part of the stump lying below ground level and throughout the root system where the roots are more than i" in diameter.

About 70$ of the larvae pupate in the roots at a distance greater than one foot from the stump. A' few of the pupal cells are made completely within the wood. When the pupal cell is complete the larva encloses itself within it by sealing the entrance with long excelsior-like chips of wood obtained while digging the cell. A short prepupal period of about three days follows, during which the prepupa is inactive.

Although Peirson (82) and Savely (102) state that H. pales breeds in pine logs as well as in stumps, Beal and

McClintick (2) claim that this is not the case in North

Carolina, but that it breeds only in the roots and stumps of dying trees. In southern Ontario, the adult weevils were attracted to the underside of freshly cut pine logs, but only a few eggs were laid and none of the resulting larvae developed to maturity. This is probably partly due to the low moisture content of the logs during dry periods, and partly to competition from immature stages of p. approximatus and Ips rjini(Say), a bark beetle that attacks freshly cut. 73

pine logs in large numbers. In the ten study trees cut in

1956, about 80$ of the H. pales larvae developed in the roots

of the stump, while the remaining 20$ developed in the part

of the stump below the root collar, in and around the crotches

of the main roots. Bark traps and potted seedlings set up in the field showed that overwintered adults, feed and search for breeding material until about the third week in June, and then devote most of their time to egg laying in dead or dying stumps. The feeding damage is light during July and

August, but becomes heavy again in mid-September when the new. adults begin emerging. There are, therefore, two feeding periods per year, one in the spring and one in the fall.

Following a cutting operation there are three feeding periods

on surrounding regeneration before the weevil population

subsides, as reported by Peirson (82)? the first is in the

spring following the cutting, by adults attracted to the freshly cut stumps from the surrounding area; the second is

in the fall of the same year after the new adults have

emerged from the stumps; and the third is in the following

spring by the large adult population that overwintered in

the area.

Peirson (82) states that there is a mass flight period about mid-June from cut-over areas, particularly in the third

year of infestation. This habit has not been noted in south- 74

em Ontario. It should be remembered, however, that Peirson was referring to weevil populations associated with lumbering operations, so that when the available breeding material was used up, the adult weevils had to move,,of necessity, to a new area for breeding purposes. In southern Ontario, on the other hand, the weevil is associated mostly with Christmas tree plantations, where selective cutting is practised and a continuous supply of breeding material is available to the weevil. Under these conditions it is not necessary for mass migration to take place.

Limiting Factors?

In a pine stand where white pine, red pine, and Scots pine grow in approximately equal numbers, white pine stumps were preferred over red and Scots pine stumps,as feeding and breeding material. Throughout the season about 55$ of the adult weevil population found in the soil was on white pine stumps, while 29$ and 16$ were on red and Scots pine stumps respectively. Apparently the laying habits of the females are not altered by the host, for the number of young larvae found in the stumps were always in proportion to the number of laying females irrespective of the host.

Since the eggs are laid in niches in the inner bark of the stumps and roots, they are well protected from environ- 75

mental hazards. The initial loss of 23$ of the eggs due to failure to hatch is the only factor seriously affecting the egg population.

In areas where the weevil population is heavy, competi• tion for food in the larval stage becomes serious and may cause the death of 70$ or more of the young larval population.

Dendroctonus valens Lee., a bark beetle that attacks weak pine trees and freshly cut stumps, may at times almost com• pletely exclude the H. pales population from stumps. While the larvae are actively feeding they are relatively free from attack by mites. However, during the prepupal period, if mites are successful in entering the pupal chamber, they may inflict a sufficient number of wounds to kill the pre• pupa. About 2$ of the prepupae are killed in this manner.

It is only with difficulty that mites can enter the pupal cells, for while the excelsior-like outer layer of the "chip cocoon" is easily penetrated, a second inner layer of fine closely packed wood dust is practically impenetrable. A

Braeonid parasite plays a minor role in controlling the weevil. The ratio between this parasite and adult weevils emerging from stumps kept in cages, was about 1 % 200.

Mortality in the adult stage was heaviest during the second overwintering period. About 36$ of the young adult population emerging in the fall died during the first winter and about 45$ during the second winter. The remainder died

during the second growing season. None of the adults reared

in the insectary survived to enter a third period of hiber•

nation.

The most important limiting factor of H. pales is the

quantity of available breeding material in the field. Until

recent years, damage to pines caused by the weevil has not been as extensive in southern Ontario as reported in the

United States. This is probably due to the fact that there had been no large-scale cutting operations of pines in the area for some time, thus preventing a buildup of the weevil population. Since 1945, however, the Christmas tree industry

has expanded greatly and large cutting operations of six-,

seven-, and eight-year-old trees have been made during the past few years. The stumps of these trees, left in the

ground to rot, were heavily infested by H. pales with the

result that it now occurs in epidemic numbers in Simcoe

'County and Durham County and generally in the area west of a line drawn through Port Severn and Trenton. In areas where

the damage is heaviest, up to 40$ of the branches of five-

to ten-year-old pines have been killed or discoloured over

the whole stand (52). 77

Effect on the Tree?

H. pales adults will feed on the tender hark of twigs and small branches of pines from the seedling stage up to mature trees. Tyhere the weevil population is high this may result in the death of seedlings and young trees up to ten years of age, and of individual branches on larger trees.

The damage is of particular importance to Christmas tree growers, for the market value of trees is greatly lowered by the presence of damaged or dead branches.

SIGNS AND SYMPTOMS? The feeding damage of H. pales is very similar to that of H. radicis. The adults chew - small pits about in diameter through the bark to the wood.

Where high populations exist;-..the pits are so numerous that they join together to form larger wound areas that eventually girdle the stem or branch. Oftentimes the bark of seedlings is completely removed. Fresh damage may be identified readily, but sap exuding from the wounds soon fills up the small pits and upon solidifying, hides them by covering the branches with resin. Girdled branches and trees can be spotted easily at a distance by their brown colour. 78

PISSODES APPROXIMATES HOPK.

Pissodes approximatus Hopkins (71).

BIOLOGY: Britton (10, 11, 13), Wells (124), Anon

(1), Boving (9), Plummer and Pillsbury (93),

Knull (72, 73), Peirson (88, 89), Easterling

(24), Pelt (35, 36, 48), Plumb (90, 91),

Schaffner (103), Pelt and Bromley (49, 50),

Stewart (116), Priend (55, 56), Bess (3).

History?

P. approximatus was described in 1911 by Hopkins (71), who stated that it bred in the thick bark of the tree, some• times causing serious damage to the sapling stage. In 1929,

Boving (9) discussed the taxonomic differences between the mature larvae of p1. ^approximatus and P. strobi. Plummer and pillsbury (93) reported that although the breeding habits' of the two weevils differed their seasonal histories were very similar,, and suggested that they might prove to be one species since they had been successful in rearing P. strobi experi• mentally in the trunks of weakened trees. That they are indeed different species is shown by the difference in their chromosome numbers (S. G. Smith, unpub.,) and the absence from P, strobi of the chromosomal polymorphism reported in 79

P. approximatus (113). The importance of p. approximatus as a secondary pest in areas where pines have been weakened by defoliators, bark beetles, or by transplanting, has been pointed out by Easterling (24), Pelt (36), Schaffner (102), and Stewart (116).

There is at present only scant information available on the bionomics of this weevil, and its present status in the northeastern United States is not clear, although Holt

(69) has reported that it is becoming an increasingly serious pest in coniferous plantations in the State of Pennsylvania.

Description of Life History Stages;

ADULT: The adult P. approximatus is a typical cur- culionid and closely resembles P. strobi (pig. 21). It varies considerably in size, being from 5 to 8 mm. in length and from 2 to 3 mm. in width. The females are, on the average, than 1 mm. longer the males. The newly emerged adult is medium brown, darkening to almost black after having overwintered.

The prothorax, elytra, and legs are marked with tufts of white and reddish-brown scales grouped to form several small spots on the prothorax and usually two irregular bands across the elytra. The curved snout is slender and about as long as the prothorax, with the antennae attached about mid-way along its length. Hopkins (71) separates P. approximatus from p. Fig. 21. Pissodes approximatus

adult xl2.

strobi by the "average large size, elongate body, the sides of the elytra more distinctly narrowed posteriorly. The beak is longer, the spots of the elytra are uniformly smaller, the posterior ones rarely connected".

EGG: The egg is ovoid and measures 0.80 ± 0.04 mm. in length and 0.50 t 0.03 mm. in 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. Distribution of head capsule measurments of pissodes approximatus larvae.

egg varies considerably, some being almost spheroid. The volume of the egg, however, is relatively constant. When first laid it is almost colourless with a smooth glistening chorion,

LARVA.: The larva is typically curculionid in form, When fully grown it is about 12 mm, in length with a light brown head and a white body. The 42 weevils reared from eggs in •the insectary all passed through four larval instars. Fig. 22 illustrates the distribution 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 linear regression relationship

Dyar' s Rule ' Linear regression Instar i Observed width Calcu- $ s Calcu- Per cent \ * Per cent lated : >, lated error error width j ! width • I J! 0.354 : p;285 +19.5 • • # II ! 0.512 * 0.534 ? -4.3 \; 0.568 0* -10.9 • • • III 0.755 • 0.805 i -6.6 : 0.852 -12.9 $ » IV iI 1.218 +0.2 !t + 6.8 * 1.215 I 1.135 #> * * • m * # •

width of reared larvae as they developed through each instar from the egg to the pupal stage. A. field check was made on the las.t instar by measuring the head capsules of 112 pre- pupae collected in the field from chip cocoons. The hatched polygon in Pig. 22 represents these measurments and indicates good agreement with measurments of the reared material.

Table VI shows a comparison between the observed head capsule widths and those estimated using Dyar's Rule and on the basis of a linear regression relationship. It is evident that the increase in width from one instar to the next follows Dyar's

Rule more closely than the linear regression suggested by

Ghent (59) for certain sawflies.

PUPA? The pupa is completely white when first formed, but the mandibles, eyes, rostrum, prothorax, and legs become medium brown before adult emergence.

Distribution and Hosts?

In his original description, Hopkins (71) reported the following pines as host plants?

Pinus strobus L. Eastern white pine. " rigida Mill. Pitch pine. " banksiana Lamb. Jack pine. " echinata Mill. Shortleaf pine. " resinosa/JLit. Red pine. " virginiana Mill. Virginia pine. " pungens Lamb. Table mountain pine,

It. has since been reported breeding in Mugho pine (48) and

Scots pine (90, 116). Hopkins recorded its distribution as

Wisconsin, Michigan, Pennsylvania, New York, Mew Hampshire,

Massachusetts, Virginia, West Virginia, and North Carolina in the United States, and southern Ontario in Canada. Since

1911, P. approximatus has also been recorded in Connecticut

(10) and Ohio (24). In Ontario, the author has collected 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. ^>^< HP ADULT 1

EGG lip

LARVA IP m PUPA •

ADULT wk

EGG IIP wk B 1

LARVA wk III ii

PUPA lip « —™ lip IIP ADULT • Pig. 23. Seasonal history of pissodes appro•

ximatus in southern Ontario.

part of the province.

Seasonal History?

In southern Ontario, P. approximatus overwinters in

the larval, pupal, and adult stages. This, together with

the fact that there is a long oviposition period, leads to

a complicated seasonal history with generations of both 85

one and two years duration (Fig. 23). The majority of the population overwinters in the adult stage. The remainder overwinters in the larval and pupal stages to emerge as adults in late June and July 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 indistinguishable.

The first egg was found in the field during the 1956 growing season on. May 26, while in the insectary the first egg was laid on June 13. Most of the females lay their quota of eggs before the end of the first week of July and then die. The adult population in the field, therefore, declines rapidly early in July, but a few females continue laying until early September.

The developmental period of the 42 weevils reared from egg to adult in 1956, was about 60 days. Table VII shows the average duration of the egg stage, the four larval instars, and the pupal stage of insects reared in an unheated insectary during the summer months.

Habits?

The adult weevils overwinter in the duff and top soil 86

overlying the roots and under scales and in crevices of the rough outer hark of pine trees. They emerge in early May and feed for about three weeks on the inner bark of pine branches and on the stem of seedlings and small trees. The underside of low-lying branches in contact with the litter are par• ticularly attractive as feeding sites.

TABLE VII

The duration of the immature stages of Pissodes approximatus reared in an unheated insectary during the summer months

Stage J Time (days)

Egg • 8.6 + 1.6

# «-- + 1st instar 0 3.6 0.5 + 2nd instar 3.9 0.8 % 3rd instar 4.9 + 0.9 % 4th instar 24.0 + 6.1

Pupa 14.8 + 0.7

«*

During the latter half of May, there is a mass flight period when the weevils search for suitable breeding material.

Mating takes place at this time and oviposition begins about late May, Dead or dying trees of all 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 •§-" in diameter.

In seedlings, where the bark is too thiit to accommodate mature larvae, the larvae bore to the center of the stem, where they pupate.

The eggs may be laid throughout the trunk and large

branches, but the rougher bark at the branch nodes seems to be preferred. In the insectary, 12 females laid an average

of 49 eggs each, with one laying 102. The eggs are deposited,

in pockets; chewed in the inner bark by the females. They are

normally laid individually in the pockets, but frequently

groups of four or five eggs may be found together.

The newly hatched larvae are very small, measuring about 1 mm. in length. Immediately upon hatching they begins

feeding in the cambial layer. They normally mine in either direction along the grain of the wood unless interrupted by

obstacles, in which case they either change direction through o * 180 or work around the obstacle and continue with the grain

of the wood (Pig. 24). y«4ien the larvae attain maturity, they

construct chip cocoons typical of the genus Pissodes in the

outer surface of the wood (Pig. 25). Pupal development takes place in these chambers and requires three or four days.

Newly formed adults remain in the pupal chambers about five days before chewing their way to the outside, when the cuticle 88

Pig. 24. Larva of pissodes app•

roximatus in rearing. Note larval

mines parallel to the grain of the

bark.

soon hardens and darkens to a medium brown. The first adult emerged in cages in 1956 on July 26 followed by a sustained high emergence from about August 15 to September 10. The sex ratio of emerging adults was approximately 1 j 1. The new adults feed from the time of emergence until the onset of cold weather, but the females do not mate or oviposit until the following summer.

Logs infested in June, 1956, produced an average of

216 adults per square foot of bark, while logs infested in Pig. 25. "Chip cocoons" of pissodes approximatus showing, (a) one cell intact and (b) another opened to reveal the prepupa inside. Note the excelsior-like covering of the cells. 90 ,91

early September produced only 51 adults per square foot. It must be remembered, however, that the relative percentage of each stage overwintering depends to a large extent on the time of the year the breeding material becomes available to the weevils. In southern Ontario, where large populations of the weevil are usually associated with Christmas tree cutt• ings, the stumps of trees cut in the fall are invaded in late May and early June the following year, and this results in a large emergence of adults in August and September,

Breeding material available later in the summer is relatively limited, resulting in only a few overwintering larvae and pupae?.

Limiting Factors?

Since P. approximatus is a secondary insect incapable of attacking healthy pines successfully, the main factor limiting its population density is the availability of suit• able breeding material. Under natural conditions this, factor keeps the weevil population low. In areas where pines are grown in pure stands and the stumps of harvested trees are left in the field to rot, however, populations rapidly build up to epidemic proportions.

Several other factors of lesser importance operate in controlling the population of p. approximatus. During the 92

Pig. 26. Stem of a three-inch

red pine infested with Pissodes

approximatus (pupal stage).

1956 growing season up to 35$ of the larval population was killed by a vipionid 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, parti•

cularly in trees where the stem is heavily infested through•

out its length (Pig. 26). In I956 the downy woodpecker, Fig. 27. Four-inch Scots pine stump in•

fested with pissodes approximatus and Hylobius

pales (pupal stage). The lack of pupal cells

above ground level is due to competition

from bark beetles.

Dendrocopus pubescens medianus (Swainson), destroyed up to

90$ of the weevil population in individual trees by com• pletely stripping the bark from the stem and large branches in search of food. Weevil populations in stumps, however, were found to be practically free from attack by birds (Fig.

27); they are nevertheless subject to serious competition from two bark beetles, Dendroctonus valens Lec. and Ips pini (Say), and H. pales. 94

Effect on the Tree?

Although P. approximatus normally breeds in dead or dying pine material, it can successfully attack seedlings ., and weak trees for breeding purposes, causing the plants to die. This type of damage was particularly noticeable in seedlings of Austrian pine in the Midhurst Nursery, where about 9fo were killed by the weevil in 1956. Recently trans• planted five- to ten-year-old ornamental stock was also heavily attacked in the Angus area in 1956 and 1958.

SIGNS AND SYMPTOMS? Fresh feeding wounds made by P. app• roximatus are somewhat different from those made by H. radicis an^ S» pales. Ihereas the Hylobius adults chew irregular pits in both the outer and inner bark, p. approximatus leaves the outer bark intact except for small punctures through which it inserts its beak and chews out larger areas of the

inner bark. This, makes the feeding damage of P. approximatus less noticeable when it is fresh, but when the bark on the injured twigs become weathered the outer bark flakes off and the feeding damage resembles that of the other species. 95

DISCUSSION AND CONCLUSIONS

At the time when the present investigations were under• taken, available information on H. radicis, H, pales, and

P. approximatus was based mainly on observations made in the New England States, Minnesota, and Wisconsin and applied to problems somewhat different from those in southern Ontario,

It became apparent at that time that conditions brought about primarily by the Christmas tree industry during the previous ten years were ideal for the buildup of large weevil popula• tions and that this presented a serious threat to plantation grown pines, whether planted as Christmas trees or in county forests.

In the present work the previous information existing on the three weevils has been brought together and interpreted in the light of observations made in southern Ontario, The ecology of the weevil complex has been investigated to the extent that the bionomics and cause of outbreaks are well understood, and the main limiting factors of the weevil / • populations, are known.

With this newly acquired knowledge, it is possible to appraise the weevil problem in southern Ontario in a manner not possible previously, and to draw certain conclusions and make recommendations on practical methods of growing pines in pure stands relatively free from weevil attack.

Basically, the weevil problem in southern Ontario is of a silvicultural nature. The three weevils are native species and are not known to occur in large numbers except where pines are grown in pure stands or where large cutting operation of pines have taken place. H. radicis differs in habits from H. pales and P. approximatus mainly in that it attacks and breeds in healthy pines, while the latter two species breeds only in dead or decadent pine material. Since

H. radicis occurs in epidemic number only in puref stands where exotic pines such as Scots, Austrian, or mugho are present in large numbers, one method of coping with the wee• vil is to avoid the planting of pines in such mixtures. This is not always desirable, however, for in southern Ontario

Scots pine has a greater market value as a Christmas tree than any other species and is consequently grown extensively in pure stands. In such areas it may be necessary to control

H. radicis by means other than silvicultural. It was found in the present studies that the application of biological controls would not be practical, since all stages of the weevil are well protected from predators, parasites, and fungi. Stewart (117) reports that he obtained 100$ control of H. radicis infesting Scots pine in southern Ontario, by applying a dieldrin spray at the base of the trees. He has 97

also communicated directly with the author that one applica• tion of this insecticide is effective in protecting the trees from re-infestation for a period of up to three years. The main objection to the chemical control suggested by Stewart is that large quantities of water are needed for the spray.

Since most pine plantations are located on high, well-drained, sandy soils, the water problem is of paramount importance and usually ..prohibits the use of the recommended control.

Therefore, a practical control for H. radicis in southern

Ontario has not yet been achieved. This is true particularly in county forests where pines are planted to grow to maturity, for in this instance it is possible that several application of insecticide would be needed during the life of the tree to prevent re-infestation. However, when considering pines grown for the Christmas tree market it is possible that one application of insecticide would suffice. H. radicis will not attack trees less than 1-fe- inches in diameter at stump height (6 inches above ground), and a tree of this size

(usually four or five years old) needs only three or four years protection before cutting for market.

Since the area infested by H. radicis in southern

Ontario is still actively expanding, it was not possible to determine the factors limiting its distribution. However, it iwould'iseem that the soil exerts some influence on the 98

insect, for all known infestations in the area are confined to light sandy soils of low fertility. This is in agreement with reports by,Schaffner and Mclntyre (109) in the United

States. Preliminary work done on the soil in the Angus area during 1958 indicates that texture is not the only factor involved, for the weevil is conspicuously absent from certain areas where the soil is light and sandy, although heavy in• festations abound in the immediate vicinity. It is possible that a combination of factors such as texture, moisture con• tent, and soil reaction are acting together in limiting the distribution o:g the weevil.

H. pales and p. approximatus both breed in dead or decadent pine material and attack healthy trees only as adults for feeding purposes. Therefore, a large amount of breeding material is necessary for the weevil to increase to epidemic numbers. In natural stands where the weevil occurs in small numbers, the feeding damage is negligible and usually not noticed. It is the lack of a sound sanitation program in Christmas tree plantations and county forests that has brought about the present problem in southern Ontario.

The cutting methods used by Christmas tree growers poses serious problems to a sound sanitation program.

Normally pines are cut as Christmas trees between the ages of six and nine years in three successive years. The first 99

year a light cut is made of the more advanced trees. The second year a heavy cut is made of most of the merchantable trees followed by a clean-up out in the third year. Usually the area is replanted during the fourth year by plowing a furrow between the rows of stumps to receive the new plants.

This means that for three consecutive years large numbers of fresh stumps are left in the ground to rot and be infested by H. pales and P. approximatus. Under this cutting system the Christmas tree grower is hesitant to pull stumps after the first and second cut for fear of damaging the remaining trees. Furthermore, many plantations are located on land covered with large boulders over which a tractor could not be operated.

In view of the fact that Christmas tree growers are hesitant in pulling stumps after each cut for practical as well as financial reasons, an alternative solution to the sanitation problem is desirable. It is possible that infes• tations would be prevented if the stumps and roots of trees cut during the first and second year are kept alive by leaving the bottom whorl of large branches on the stumps, and .then pulling all the stumps after the third cut with a bulldozer or tractor.

In considering chemical controls of H. pales and P.

approximatust it is conceivable that an insecticidal spray 100

applied -to the part of the stump above ground level, would kill the greater part of the P. approximatus population when it emerges as adults. However, since over 60$ of H. pales pupate in the roots at a distance in excess of one foot from the stump and emerge directly through the soil, it would be necessary to spray the soil overlying the roots as well as the stumps to control this species. In a Christmas tree plan• tation this would mean spraying the whole ground once for every crop grown, for the root system of adjacent trees over• lap to a considerable extent.

The large quantity of water and insecticide needed for this control makes it unsuitable for general use and should be considered only as an emergency measure where a valuable crop will be lost if subjected to one more feeding season.

Spraying the foliage of trees to protect the branches from adult feeding is even more impractical, for an application of insecticide would have to be applied every year to all the trees in the stand. This would mean about eight applications per crop and would create an expense that the growers could not bear.

Plantation grown pine is subject to attack by a number of destructive insects. The weevil complex discussed in this thesis is, perhaps, the most recent such problem to attain economic importance in southern Ontario. Since insects usually 101

become problematic wherever plants are grown in concentrated numbers as a crop, it often becomes necessary either to for• mulate suitable direct controls for the pests, or to desist the planting of pure stands. Silvicultural controls are usu• ally more desirable than direct controls, for they tend to prevent insect outbreaks, while direct controls are generally applied only after the insects have reached epidemic propor• tions. There are reasons to believe that silvicultural con• trols could be used successfully against the weevils discussed here. In the Christmas tree industry, the public demand for a specific species of pine or other conifer is created largely by the grower. In the Maritime Provinces the practice is to grow balsam fir; in southern Ontario Scots pine; and in northern Ontario spruces. Strangely enough most of these trees are sold to a common distant market in the United States. It is the belief of the author that it would be profitable for growers to operate co-operatively, planting a crop of mixed conifers instead of only one species. This would limit greatly the ravages of several insect pests that have become increas• ingly important in plantations during the past fifty years, by reducing the density of their favorite food or breeding material.

The weevil problem on pines in southern Ontario still

exists, and the Christmas tree industry is seriously threa- 102

tened in several areas. There is a need for further ecologi• cal investigations to determine the importance of such factors as soil, climate, stand composition, and management as they affect weevil density and the Christmas tree industry. 103

BIBLIOGRAPHY

(1) ANON. 1927. The relation of insects to slash disposal.

TJ. S. Dept. Agr., Circ. 411. 12.

(2) BEAL, J. A., AND K. B. McCLINTICK. 1943. The pales

weevil in southern pines. J. Econ. Ent., 36(5)?

792-794.

(3) BESS, H. A. 1944. Insect attack and damage to white

pine timber after the 1938 hurricane in New

England. J. Por., 42: 14-16.

(4) BLAIS, J. R. 1958. Effects of defoliation by spruce

budworm (Choristoneura fumiferana Clem.) on radial

growth at breast height of balsam fir (Abies bal-

samea (L.) Mill.) 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 II. 340.

(7) ' 1842. In Schonherr's Genera et Species.

Curculionidum VI. 300.

(8) BOURNE, A. I. 1940. Pales weevil (H. pales). U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv. 20: 191. 104

(9) BOVING, A. G. 1929. Taxonomic characters for the

identification of the mature larvae of pissodes

strobi 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•

ecticut Entomologist for 1917. Conn. Agri. Expt.

Sta., Bull. 203. 231-370.

(11) 1920. Nineteenth report of the Conn•

ecticut Entomologist for 1919. Conn. Agri. Expt.

Sta., Bull. 218. 112-208.

(12) 1925. Twenty-fourth report of the Conn•

ecticut Entomologist for 1924. Conn. Agri. Expt.

Sta., Bull. 265. 340.

(13) 1929. Twenty-eightA report of the Conn•

ecticut Entomologist for 1928. Conn. Agri. Expt.

Sta., Bull. 305. 666-768.

(14) BRITTON, W. E. AND M. P. ZAPPE. 1927. ^Hylobius pales

Hbst^. Conn. Agri. Expt. Sta., Bull. 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-

tera: Curculionidae). Proc. Ent. Soc. Wash., 36: 105

252-2 56.

(17) CARTER, E. E. 1916. Eylobius pales as a factor in the

reproduction of conifers in New England. Proc.

Soc. Amer. Foresters, 2(3).s 297-307.

(18) CONKLIW, J. G, 1941. Pales weevil (H. pales). 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., Circ. 411. 4.

(20) 1950. Insect enemies of eastern

forests. TJ. S. Dept. Agr., Misc. Pub. 657.

285-286.

(21) DIETRICH, H. 193L Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 11: 28.

(22) 1932. Pales weevil (H. pales). U. S.

Dept. Agr,, Bur. Ent. plant Quar., Ins. Pest

Surv.,12: 31.

(23) DODGE, R. l874.£kylobius pales Hbst^J . Rural Caro•

linian, V. 476.

(24) EASTERLING, G. R. 1934. A study of the insect fauna

of a coniferous reforestation area in south•

eastern Ohio. Ohio J. Sci., 34s 129-146.

(25) EBEL, B. H. AND C. P. SPEERS. 1957. Population studies 106

on the -pales weevil (Hylobius pales). Proc.

Assoc. South. Agri. Workers, 54: 153-154.

(26) EDDY, B. 1941. Pales weevil (H. pales). TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins Pest Surv.,

21: 208.

(27) PELT, E. P. 1906. Insects affecting park and woodland

trees. Mem. N.< Y. State Mus., 8j 877.

.(28) 1923. ^Hylobius pales Hbst.J . N. Y. State

Rept., 35? 86.

(29) 1924. In Manual of tree insects. 229.

(30) 1926. Pales weevil (H. pales). TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 6:

172-173.

.(31) • 1926. Pales weevil (H. pales). TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 6:

296.

(32) 1926. Pales weevil in a new role. J. Econ.

Ent., 19(5); 795.

(33) 1928. Observations and notes on injurious

and other insects of New York State. N. Y. State

Mus. Bull. 274. 145-176.

(34) 1931. Pales weevil (H. pales). U. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 11: 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 insects

in 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. pales). TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 16s

487.

(39) 1936. A weevil (Hylobius radicis Buchanan).

TJ. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 16$ 417. .. ..

(40) 1938. Scotch pine weevil (Hylobius radicis

Buch.). TJ. S. Dept. Agr., Bur. Ent. Plant Quar.,

Ins. Pest Surv., 18$ 22-23.

(41) 1939. A weevil (H. radicis). TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv.,

19s 405.

(42) 1940. Pine root weevil (H. radicis). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins..Pest

Surv., 20$ 21...

(43) 1940. A pine weevil (H. radicis). TJ. S. 108

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 20$ 191.

(44) 1941. Pales weevil (H pales). U. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21$ 54.

(45) 194L A weevil - H. radicis. TJ. S. Dept.

Agr., Bur. Ent. Plant Quar., Ins. Pest Surv., 21: 110.

(46) 1941. Pales weevil (H. pales). TJ. S. Dept.

Agr,, Bur. Ent. Plant Quar., Ins. Pest Surv., 21s

208.

(47) 1941. Weevils (Hylobius sp.). TJ. S. Dept.

Agr,, Bur. Ent. plari^ Quar., Ins. Pest Surv., 21: 465.

(48) 1941. A pine weevil (P. approximatus),

TJ. S, Dept. Agr., Bur. Ent. plant Quar., Ins.

Pest Surv., 21: 606.

(49) FELT, E. P. AND S. ¥. BROMLEY. 1937. Scientific con•

tributions. Bartlet Trees Res. Lab., Bull. 2.

1-24.

(50) 1941. New and unusual .

shade tree pests. J. Econ. Ent.,. 34(3): 383-386.

(51) 1942. The increasing

importance of coleopterous borers in shade, trees. 109

J. Eoon. Ent., 35s 169-171. .

(52) FINNEGAN, R. J. 1956. Weevils attacking pines in

southern Ontario. Can, Dept. Agr., Div. For. Biol,

Bi-monthly Prog. Rept., 12(2): 3.

(53) PITCH, A. 1859. In Fourth report of noxious insects of

New York. Albany, 66.

(54) FRIEND, R. B. 1937. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. plant Quar., Ins. Pest

Surv., 17? 461.

(55) 1940. Thirty-nineth report of the Conn•

ecticut Entomologist for 1939. Conn. Agri. Expt.

Sta., Bull. 434. 222-322.

(56) 1944. Forty-third, report of the Conn•

ecticut Entomologist for 1943. Conn. Agri. Expt.

Sta., Bull 481. 235-324.

(57) FRIEND, R. B. AND H. H. CHAMBERLIN. 1942. Forty-first

report of the Connecticut Entomologist for 1941.

Conn. Agri. Expt. Sta., Bull. 461. 463-548.

(58) GERMAR, E. F. 1824. In Insectorum species novae, Halae,

24«; 319.

(59) GHENT, A. W, 1956. Linear increment in width of the

head capsule of two species of sawflies. Canad,

Ent., 885 17-23.

(60) GLASGOW R. D. 1935. Pales weevil (H. pales). TJ. S. 110

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 13: 135.

(61) 1936. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 16s 206.

(62) HARRINGTON, ?f. H. 1881. In Eleventh annual report of

the Entomological Society of Ontario. 1880. 52.

(63) 1884. In Fourteenth annual report

of the Entomological Society of Ontario. 1883.

55.

(64) HARRIS, T. ¥. 1841. In Report on the insects of Mass•

achusetts injurious to vegetation. Cambridge,

Mass. 459.

(65) 1862. In Report on the insects of Mass•

achusetts injurious to vegetation. Cambridge,

Mass. 70.

.(66,) .1'HERB ST, 'J. F. W. 1797. In Zafer, VII: 31.

(67) HETRICK, Li A. 1941* Pales weevil (H. pales). TJ. S.

Dept. Agr.,, Bur. Ent. Plant Quar., Ins. Pest

Surv., 21: 110.

(68) HINDS, J. 1909. In Alabama Bull. I46. 101.

(69) HOLT, ¥. R. 1956. Certain aspects of the biology of

four weevils attacking coniferous plantations

in central Pennsylvania. M. For. Thesis, Penn- Ill

sylvania State University.

(70) HOPKINS, A, D. 1904. In United States Department of

Agriculture, Bull 48. 34.

(71) 1911.>I. Contributions toward a mono•

graph of the bark weevils of the genus Pissodes.

U. S. Dept. Agr.,. Bur. Ent. ,PTe.ch. f.Ser., No. 20.

1-68.

(72) KNOLL, J. N. 1931. Pales weevil (H. pales). U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest :..

Surv., 11j 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 prarie Parmer. 42:

(75) LECONTE, J. L. 1876. In Proceedings of -the American

Philosophical Society. XV". 140.

(76) 1885. In Transactions of the American

Entomological Society. XII. 30.

(77) LYLE, C. 1937. Pales weevil (H. pales). 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 radicis Buchanan. J. Econ. Ent.,

30s 215-216. 112

(79) PACKARD, A. S. 1878. Guide to the study of insects.

New York. 715.

(80) 1881. In Insects injurious to forests

and shade trees. TJ. S. Ent. Comm., Bull. 7. 275.

(81) 1890. Insects injurious to forests and

shade trees. Fifth Rept. TJ. S. Ent. Comm., 724.

(82) PEIRSON, H. B. 1921. The life history and control of

the pales weevil (Hylobius pales). Harvard For.,

Bull. 3. 33p.

(83) 1922. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 2? 144. (84) 1922. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 2$ 255.

(85) 1923. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 3: 332.

(86) 1923. In Maine forest service. Bull.

1. 33.

(87) 1927. In Maine forest service. Bull.

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. Ent. Plant Quar.,, Ins.

Pest Surv., 16s 346.

(91) 1936. A weevil (Hylobius radicis Buch.).

U. S. Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 16s 384.

(92) 1937. Thirty-sixth report of the Connec•

ticut Entomologist for 1936. Conn. Agri. Expt..

Sta., Bull. 396. 289-415.

(93) PLUMMER, C. C. HAD A. E. PILLSBURY. 1929. The white

pine weevil in New Hampshire. N. H, Expt. Sta.,

Bull. 247. 32p. . .

(94) PRENTICE, R. M. 1955. Pine root collar weevil in

Manitoba. Can. Dept. Agr., Div. For. Biol. Bi•

monthly Prog. Rept., ll(4)s 1.

(95) PRICO, ¥. A. 1940. Pales weevil (H. pales). U. S. Dept.

Agr., Bur. Ent. plant Quar., Ins. Pest Surv., 20: 350.

(96) PROVANCHER, L. 1877. Petite faune entomologique du

Canada, I. Nat. Can. 9: 515. 114

(97) ROBINSON, J. M. 1938. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 18: 128.

(98) 1940. Pales weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. plant Quar., Ins. Pest

Surv., 20$ 63.

(99) ROELOPS, W. 1884. In Transactions of the American

Entomological Society. XEI. ; 1884T1885.'.30. .

(100) SAUNDERS, W. 1884. In Fourteenth annual report of the

Entomological Society of Ontario. 1883. 55.

(101) 1883. In Report of the fruit growers

association of Ontario. 32 5.

(102) SAVELY, H. E. 1939. Ecological relations of certain

animals in dead pines and oak logs. Ecol. Monogr.,

9(3): 322-385.

(103) SCHAFFNER, J. V.- 1936. Rhyacionia buoliana. U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 16: 302.

(104) 1939. A weevil (H. radicis). U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 19$ 165.

(105) 1939. A weevil (H. radicis). U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 19$ 577. 115

(106) ; 1940. A weevil (H. radicis). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 20$ 277.

(107) 1940. A weevil (H. pales). TJ. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 20$ 412, 509.

(108) ; 1941. A weevil (H. radicis). U. S.

Dept. Agr., Bur. Ent. Plant Quar., Ins. Pest

Surv., 21$ 110. 657.

(109) SCHAFPNER, J. V. AND H. L. McINTYRE. 1944. The pine

root collar weevil. J. For., 42(4)$ 269-275.

(110) SENTELE, N. ¥. 1949. Pales weevil damages plantations

in Louisiana. J. Por., 47(9)$ 741.

(111) SHENEPELT, R. D. 1950. Control of the pine root

collar weevil. J. Econ. Ent., 43(5): 684-685.

(112) SMITH, J. B. 1877. [Tne pales weevil, Hylobius pales

Hbst/y. Peoria. 29.

(113) SMITH, iS. G. 1956. Chromosomal polymorphism in a

bark weevil. Nature, 177$ 386.

(114) SPEERS, C. P. 1956. Pales weevil controlled with

insecticides: first year results. Southeast.

Por. Expt. Sta., Res. Note 96.

(115) C 1957. Pales weevil controlled with

sprays and dips. Assn. South. Agri.. "Corkers, 116

Proc, 129-130.

(116) STEWART, K. E. 1942. Pissodes approximatus Hopk. on

white pine. Can. Ins. Pest Surv., May.

(117) 1958. Chemical control studies on the

pine root-collar weevil Hylobius radicis Buch.

in southern Ontario. Can. Dept. Agr., Div. Por.

Biol. Interim Rept., 1957-2. 9p.

(118) THATCHER, R. C. 1957. Pine reproduction weevilss

preliminary results from 1955-1957 studies.

Southern Por. Pest Reported, U. S. Dept. Agr.,

18s 2.

(119) THOMAS, C. 1880. In Report on noxious and beneficial

insects of Illinois. 111. Agr. Expt. Sta., VI.

174.

(120) WALLACE, D. R. 1954. The pine root collar weevil in

Ontario. Can. Dept. Agr., Div. Por. Biol. Bi•

monthly Prog. Rept., 10(3): 2.

(121) WARREN, G. L. 1956. Observations on the origin of

infestations of the pine root collar weevil in

plantations. Can. Dept. Agr., Div. Por. Biol.

Bi-monthly Prog. Rept., 12(3): 2.

(122) 1956. -The effect of some site factors

on the abundance of Hypomolyx piceus (Coleopteraj

Curculionidae). Ecology, 37(1)j 132-139. 117

(123) WATSON, W. Y. 1955. A description of the full-grown

larva of Hylobius radicis Buch. (Coleoptera:

Curculionidae). Canad. Ent., 87(1)$ 37-41.

(124) WELLS,A. B. 1926. Notes on Hylobius pales Boh. and

Pissodes strobi Peck as nursery pests. J. Econ. Ent., 19(2): 412-413.

(125) WOOL, S. L. 1957. The North American allies of

Hylobius piceus (DeG/reer) (Coleoptera: Curcu•

lionidae). Canad. Ent., 89(1): 37-43.

(126) YORK, H. H. 1933. Some observations on Hylobius

pales Herbst. J. Econ. Ent., 26: 218-221.