This dissertation has been microfilmed exactly as received

Mic 60-4082

FORBES, Robert Shirley. BIOLOGY OF THE MOUNTAIN ASH SAWFLY, PRISTIPHORA GENICULATA (HTG.).

The Ohio State University, Ph. D., 1960 Zoology

University Microfilms, Inc., Ann Arbor, Michigan BIOLOGY OF THE MOUNTAIN ASH SAWFLY,

FRIST PHCRA GENICULATA (HTG.)

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The (Mo State University

By

ROBERT SHIRLEY FORBES, B.Sc.F., M.Sc.

******

The Ohio State University I960

Approved by:

Adviser Department of Zoolo and Entomology ACKNOWLEDGMENTS

I wish to thank M. L. Prebble, Director, Forest Biology

Division, Canada Department of Agriculture, for permission to use

divisional data. Alvah Peterson and later Dwight M. DeLong, my

advisers at The Ohio State University, provided advice and encourage­

ment. I am indebted to R. E. Balch, former Officer-in-Charge, Forest

Biology Laboratory, Fredericton, New Brunswick, for guidance. W. A.

Reeks made helpful suggestions during the early stages of the work.

D. G. Mott and the late C. Reimer assisted in statistical analysis.

D. 0, Greenbank provided advice on climatological analysis. Pho­

tography was by L. E. Williams and E. B. Bates. J. Franz and

W. S tritt provided pinned sawfly adults from Germany. C. C. Smith

permitted the use of unpublished air and ground temperatures.

System atists at the Entomology Research In stitu te , Ottawa,

identified parasites and predators, and officers at the Insect

Pathology Research Institute, Sault Ste. Marie, provided disease determinations. A. E. Roland checked identification of foliage.

I am grateful to the following entomologists for infor­ mation on sawfly distribution: W. E. Waters, A, E. Brower, G. Stuart

Walley, H. G. Wylie, lories Crooke, R. B. Benson, J. Franz, Keizo

Yasumatsu, C. Watanabe, Motonori Inouye, G. T. S ilv er, C. E. Brown,

R. M. Prentice, W. L. Sippell, D. P. Connola, W. E. Smith,

i i F. A. Soraci, William M. Boyd, Paul R, F lin k , Edgar G. Rex,

A. T. Drooz, F. Waldo Craig, J. N. Knull, David E. Donley, D. M.

Benjamin, C. L. Morris, Arthur P. Morris, Theo L. Bissell, Dale

F. Bray, C. F. Speers, and F. Waldo Craig. TABLE CF CONTENTS

Page ACKNOWLEDGMENTS ...... i i

LIST OF TEXT TABLES ...... v ii

LET OF APPENDIX TABLES ...... ix

LIST OF ILLUSTRATIONS ...... x i

INTRODUCTION ...... 1

GENERAL METHODS ...... 3

TAXONOMI ...... 10

HCSTS ...... 11

Sorbus aucunaria Linnaeus ...... 16

Sorbus americana Marshall ...... 17

Sorbus decora (Sargent) Schneider . • • • 20

DISTRIBUTION ...... 21

BIOLOGY ...... 28

Summary of Life History in New Brunswick .... 28

Description and Habits ...... 28

Egg ...... * ...... 28

Larva ...... 33

Pupa ...... 41

Adult ...... 41

Frass Studies ...... 47

Sex Ratio and Reproduction ...... 51

iv V Page LARVAL HEAD WIDTHS ...... 53

HOST RELATIONSHIPS ...... 68

Effect of Insect on Host ...... 68

Growth of Host ...... 68

Defoliation and Refoliation ...... 72 i Effect of Host on Insect ...... 76

Flowering ...... 76

Numbers of Insects on Flowering and Non-flowering Leaf Clusters ...... 78

POPULATION SAMPLING ...... 80

Egg ...... * . . 84-

Larva ...... 89

Tests of Differences ...... 89 j Frequency Distribution ...... 97

Cocoon ...... • 102

NATURAL CONTROL FACTORS ...... 106

Climatic Factors ...... 106

Temperature and Humidity ...... 106

R a in fall and Wind ...... 109 I Relation Between Rainfall and Infestation Intensity • • • . • . • 109

Biotic Factors ...... 117

Parasites ...... 117

Egg P arasites ...... 117

Larval Parasites ...... 118 v i

Pag© Predators ...... 123

Insects . . . * « 123

Birds ...... 126

Mammals ...... 126

Disease ...... , , 127

Viruses ...... 127

Fungi ...... 128

B acteria ...... 129

Protozoa ...... 129

Other Factors ...... 131

Failure of Eggs to Hatch ...... • 131

Starvation ...... 132

Abundance and D istrib u tio n of Host Tree . . 132

Miscellaneous ...... 133

SUMMARY AND CONCLUSIONS ...... 137

APPENDIX ...... U 6

LITERATURE CITED ...... 167

AUTOBIOGRAPHY ...... 176

.1 LIST CF TEXT TABLES ,

Table Page i

1 Observations on period of occurrence and duration of developmental stages of P. geniculata ...... 30

2 Observations on longevity of caged adults, oviposition, incubation, and egg mortality ...... 31

3 Numbers of oocytes in six newly emerged females . . . 32

4 Sizes of male and female cocoons ...... 39

5 Classification of P. geniculata cocoomcollected at three soil lev els ...... 40

6 Observations on field-collected eggs of P. geAiculatfl...... 7 ...... 46

7 Frass drop of P. geniculata collected on a 21 x 21 square ...... 46

8 Frass yield and length of development in instars 2 to 5...... 50

9 Comparison of observed head capsule widths of larvae with those calculated by seven m ethods ...... 60

10 Radial growth of two Sorbus aucuparia tre e s in 1955 . 71

11 Observations on defoliation and refoliation of apical leaf clusters of European mountain ash trees following attacks by P* geniculata ...... 73

12 Distribution and numbers of flowering and non­ flowering leaf clusters with corresponding leaf counts by crown le v e l, crown quadrant, and ra d ia l distance on four European mountain ash trees .... 77

13 Numbers of P. genfon^fttfl larvae on flowering and on non-flowering leaf clusters on four §. aucuparia tre e s in 1953 and in 1955 ...... 79

14 Eggs and larvae of P. geniculata and estimated defoliation in four crown levels of four S. aucuparia tre e s , 1953 ...... 32

v i i v ili

Table Page

15 Eggs and larvae of P. geniculata and estimated defoliation in the outer and inner crown at four crown levels on four European mountain ash trees, 1954 ...... 85

16 Eggs and larvae and estimated defoliation in the outer and inner crown at four crown levels on four trees, 1955 ...... 86

17 Eggs and larvae and estimated defoliation in the outer and inner crown in four crown quadrants on four trees, 1954 ...... 87

18 Eggs and larvae and estimated defoliation in the outer and inner crown in four crown quadrants on four trees, 1955 ...... 88

19 Number of larvae recorded by tree and crown level . • 91

20 Analysis of variance of number of P. geniculata larvae collected by tree and crown level in 1954 and 1955 ...... 92

21 Analysis of variance of the average amounts of Juna-July rainfall in southern New Brunswick from 1936 to 1955, classified by infestation levels of P. geniculata ...... I l l

22 Insectary observations on egg hatching of P.. geniculata ...... 131

23 Observations on mortality of P. geniculata larvae in instars 1, 2, and 3 ...... 134 LET OF APPENDIX TABLES

Appendix Page Table

A Report form for P. geniculata infestations ...... 14-7

1 Head capsule measurements by i n s t a r s ...... • 148

2 Number of flowers recorded on S. aucuparia by tree and crown level in 1955 • . . . 149

3 Number of flowers recorded on S. aucuparia by tree and crown quadrant in 1955 ...... • 150

4 Differences in numbers of flowers on 5. aucuparia between the outer and inner crown by levels in 1955 . 151

5 Differences in numbers of flowers on §,. aucuparia between the outer and inner crown by quadrants in 1955 152

6 Average number of P. geniculata larvae per leaf cluster collected from eight leaf clusters at each crown lev el (A, B, C, D, from top down) and in each crown quadrant (N, E, S, 17) on four European mountain ash trees at two sampling periods. Fredericton, N. B., 1954...... 153

7 Average number of larvae per leaf cluster collected from four leaf clu sters in the outer crown and from four leaf cluster® in the inner crown at each crown level and in each crown quadrant on four trees at the f i r s t la rv a l sampling, 1954 154

8 Average number of larvae per leaf cluster collected from four leaf clu sters in the outer crown and from four leaf clusters in the inner crown at each crown level and in each crown quadrant on four trees at the second larval sampling, 1954 ...... 155

9 Average number of larvae per leaf cluster collected from eight leaf clusters at each crown level and in each crown quadrant on four tre e s a t two sampling periods, 1955 ...... 156

ix X

Appendix Table Page

10 Average number of larvae per leaf duster collected from four leaf clusters in the outer crovm and from four leaf clusters in the inner crown at each crown level and in each crown quadrant on four trees at the first sampling, 1955 ...... 157

11 Average number o f larvae per le a f c lu s te r collected from four leaf clusters in the outer crown and from four leaf clusters in the inner crown at each crown le v e l and in each crown quadrant on four tre e s a t the second sampling, 1955 ...... 156

12 Number of larvae recorded on §. aucuparia by tree and crovm quadrant in 1954 and 1955 ...... 159

13 Differences in numbers of larvae between the outer and inner crown by le v e ls in 1954 and 1955 . . . . 160

14 Differences in numbers of larvae between the outer and inner crown by quadrants in 1954 and 1955 . . • 161

15 Differences in numbers of larvae between first and second samplings by levels in 1954 and 1955 .... 162

16 Differences in numbers of larvae between first and second samplings by quadrants in 1954 and 1955 • . 163

17 Differences in numbers of larvae between the outer and inner crown in different sampling periods by le v els in 1954 and 1955 ...... 164

18 Differences in numbers of larvae between the outer and inner crown in different sampling periods by quadrants in 1954 and 1955 ...... 165

19 Average June-July rainfall in inches for six stations in southern New Brunswick from 1936 to 1955 . 166 LIST OP ILLUSTRATIONS

Figure Page

1 Lantern globe used in rearing larvae ...... 5

2 Bcoc-type cage used in mass-rearing of larvae . . . 5

3 Vials used for individual rearing of larvae . . . 5

4 Sleeve cage used in oviposition studies . . • • • 7

5 Bi-valve rearing cage used in observations of larval feeding ...... 7

6 Jelly-jar unit used in studying egg development . . 9

7 and 8 Larvae of P ristinhora geniculata (Harfcig) feeding on foliage of Sorbaronia hvbrida (Moench) Schneider 14

9 Foliage of Sorbus aucuparia Linnaeus adjacent to that of S. hvbrida ...... 15

10 Leaf of European mountain ash, Sorbus aucuparia L in n a e u s ...... 19

11 Leaf of showy mountain ash, Sorbus decora (Sargent) Schneider ...... 19

12 Leaf o f American mountain ash, Sorbus americana M a r s h a ll...... • 19

13 Leaf of false spiraea, Sorbaria sorbifolia (Linnaeus) Alexander Braun ...... 19

14 Map showing locations of collections of P. geniculata in North America, Europe, and Asia . . . 23

15 Map showing general locations and early years of collection of £. geniculata in eastern North America 26

16 Swellings on periphery of leaflets of S. aucuparia containing eggs of P. geniculata ...*••••• 29

17 Five instars of larvae of £. geniculsba ...... 34

18 Leaf of S. aucuparia partially destroyed by first- and second-instar larvae • • • • ...... 36 x i x i i

Figure Page

19 Typical sawfly defoliation on S. aucuparia . . . . 36

20 New crop of leaves of S. aucuparia produced after almost complete defoliation ...... 36

21 First phase of prepupal larva subsequent to the spinning of the cocoon ...... 42

22 Later phase of prepupal larva just prior to p u p a tio n ...... 42

23 Lateral view of pupa in process of shedding larval exuvium ...... 43

24 Ventral view of pupa in process of shedding larval exuvium ...... 43

25 Adults of £• geniculata ...... 44-

26 Frequency distribution of larval head capsule widths 57

27 Comparison of observed mean head capsule widths of ■ larvae and those calculated by seven theoretical progressions ...... 62

28 Relationship of radial growth of two S. aucuparia trees to mean weekly temperatures of the air and the g r o u n d ...... 70

29 Complete d efo liatio n o f small S. aucuparia tree . 75

30 . Refoliation of same tr e e ...... 75

31 Relationship between variance and mean for larval numbers on le a f c lu ste rs in 1954 and 1955 • • • • 101

32 Four 1-square foot earth-filled sampling trays used for collecting cocoons • • ...... • 103

33 The relation between June-July rainfall and infestation intensity of £. geniculata in southern New Brunswick over a 20-year period ...... 114

34-37 Eggs of P. geniculata parasitized Toy Trichogramma sp. apparently minutum R iley . • • • 120 x i i i

Figure Page

38 Eggs of coccinellid, Adalia bimmctata L. believed to be predaceous on eggs and larvae of £• geniculata ...... ♦ , ♦ 122

39 Unidentified parasite egg on fifth-instar larva of £. geniculata...... 122

40 Part of S, aucuparia leaflet showing normal egg pockets containing fully developed eggs of P. geniculata. and an egg pocket in which the egg has been destroyed by predators 124

41 Excised eggs of P. geniculata showing normal larval embryo and one that appears to have been sucked by predaceous insects ...... 124

42 A hemipterous predator, Podisus m aculiventris (Say) attacking a P. geniculata larva ...... 125

43 Section of cocoon removed to show mycelium of the fungus Fusarium oxvsporum Schl. emend. Snyder & Hansen protruding from the thoracic region of a dead l a r v a ...... 130

44 Dried remains of cocooned larva partially covered with a whitish fungus, Fusarium sp...... 130 INTRODUCTION

The mountain ash sawfly, Pristiphora geniculata (Hartig), is one of several species of sawflie3 that have been introduced to th is continent from Europe w ithin the pant century. This insect has been known in Europe since 1840 and in North America since 1926, and it occurs over wide areas of both continents. Economically, it is not very important, largely because its hosts are shade and ornamental trees which are seldom if ever k ille d by i t s attacks. The insect causes noticeable and occasionally complete defoliation of mountain ash tre e s, however, and to owners of such tre e s and to municipal and park authorities, the pest is a considerable nuisance that often t requires localized control by chemical methods. Scientifically, the species is of interest because little is known about it, and because it is an introduced insect rarely attacked by native parasites. It is evident, therefore, that biological studies are needed before its epidemiology can be understood or any serious program of biological control considered.-

Accordingly, studies were in itia te d in 1950 on the d is tr i­ bution, hosts, life history, habits, development, and natural control factors of the insect in the Maritime Provinces of Canada. In 1953 preliminary sampling techniques were investigated with the object of obtaining more complete information on the biology of the insect and its relationship with the host tree. In 1954- and 1955 sampling was

1 2 intensified and observations were made on the growth and flowering of the host tree and on aspects of defoliation and refoliation.

These investigations were carried out on a part time basis for eight years. Observations and collections were made on the campus and forest of the University of New Brunswick a t Fredericton.

These were supplemented by records and specimens obtained from many parts of the Maritime Provinces.

In any broad biological study certain aspects must be limited. Some lines of investigation warranting further study are pointed out. The work provides a basis for further studies of this and other specieB of d efo liato rs. GENERAL METHODS

The general methods used to observe sawfly habits and development and the techniques followed in studies of oviposit ion, larval rearing, and life history are outlined below. The particular methods used in sampling, in observations on tree growth, and in making head width analyses are discussed later.

Special surveys on the occurrence and distribution of the sawfly and its host plants were made by the Forest Insect Survey in the Maritime Provinces. Sawfly defoliation and damage was recorded on special forms (Appendix A), and sawflies and foliage samples were collected. Several thousand specimens of eggs and larvae were col­ lected by the writer. Much of this material was reared for infor­ mation on development, habits, and mortality factors. Some was preserved for measurement of larval head widths and for dissection.

Half of each sample was k illed in Peterson’s K.A.A.D. and preserved in 95 per cent ethyl alcohol and the other half was killed in 95 per cent alcohol and preserved in 70 per cent alcohol.

All rearings were carried out in a screened outdoor insectary. Sawfly material was usually reared in jelly jars or in lantern globes arranged so that the stem of the foliage was immersed in water (Figure l). The latter containers proved more satisfactory.

Occasionally when large numbers of larvae were involved, they were reared on stem-immersed foliage within large box-type screen cages

(Figure 2). As larvae approached maturity peat moss or vermiculite 3 Figure 1. Lantern globe and Mason jar rearing unit for larvae. Jar contains w ater.

Figure 2. Box-type cage used in mass rearing of larvae. The top and back of cage are of 32-mesh plastic screening. A sliding glass panel is in front.

Figure 3. Vials used for individual rearing of larvae. The corks are bored to accommodate shell vials of water, into which the petioles of the leaves are inserted.

k Figure 3 6

was added to the rearing containers as a cocooning medium. The

containers were transferred to cold storage in late October. Up to

1954- this consisted of a concrete compartment beneath the floor of

the insectaiy where temperatures sometimes dropped below freezing.

Later, cold room facilities were available, where material was kept

at temperatures between 32° F. and 40° F. The material was usually

left in cold storage until early May, when it was placed in the

insectary for adult emergence.

As eggs hatched in the field, first-instar larvae were

collected for individual rearings in vials (Figure 3). Feeding habits, colour changes, and numbers of instars were observed in the material reared. Observations were made simultaneously on larval colonies in the field.

When cocoons were placed in the insectary for adult emergence in the spring, and in the summer between generations, several were opened and the larvae placed in gelatin capsules for observations on pupal development.

Many adults th a t emerged from cocoons in the insectary were placed in sleeve cages (Figure 4) for observations on mating and ovi- position, and in bi-valve rearing cages (Figure $), similar to those designed by Wilder (l95l), for observations on larval feeding. Some adults were preserved for dissection and morphological examination.

Emphasis in oviposition studies was given to numbers of eggs laid, site of deposition, incubation, parasitism, and predation.

The cages were removed when egg-laying was completed. A fter eclosion, 7

Figure 4- Sleeve cage used in oviposition studies.

Figure 5. Bi-valve rearing cage used in observations of larval feeding. Upper part is celluloid; the lower part is 16-mesh fibreglass screening. the larval colonies were observed daily until specimens began to wander and feed singly. Simultaneously, foliage containing several hundreds of eggs was placed in jars in the insectary for obser­ vations on development, general mortality, and parasitism. This foliage was kept fresh for periods up to two weeks by f illin g a Je lly jar with water and placing another jar on top of it in an inverted position, the two being separated by thin cardboard containing a small hole through which the petiole of the egg-bearing leaf was inserted

(Figure 6).

Frass was collected in a 21 x 2 1 cotton-bottom frass tray placed under the crown of a moderately infested tree from June 30 to

August 3, to assess total and peak feeding periods and to determine the general effects of temperature on daily frass drop. Also, frass pellets from individually reared male and female larvae were counted and weighed to obtain evidence of the relation between frass yield and development in each instar. 9

Figure 6. Jelly-jar unit used in studying egg development. The end of the leaf petiole is in water. TAXONOIvK

The mountain ash sawfly, Pristiphora geniculata (Hartig), belongs to the order Hymenoptera, suborder Symphyta (= Chalastogastra), family Tenthredinidae, subfamily Nematinae, and tribe Nematini (Ross,

1951j Benson, 1958). The sawfly was o rig in ally described as Nematus geniculatus by Hartig (I84 O). Brischke and Zaddach (1882, 1883) illustrated the larvae in 1882 and described the larvae and adults in 1883 under the name Nematus cheilon Zaddach. Konow (1890), in revising the Tenthredinidae of Europe, placed the species in the genus Pristiphora. reduced cheilon Zaddach to synonymy, and retained

Hartig*s geniculata. Since that time descriptions or keys to the species have been included in European works by Konow (1902),

Enslin (1912-1917), Morice (1922), Lorenz and Kraus (1957), and

Benson (1958), but the generic and specific status of the insect has remained unchanged. As indicated by Schaffner (1936), when the insect was first discovered in the United States it was tentatively named Pristiphora sp. near banks 1 Marlatt, but it was later identi­ fied as P. geniculata by Dr. H. H. Ross.

10 HOSTS

In North America the most common hosts of the sawfly are the European mountain ash, Sorbus aucuparia Linnaeus, the American mountain ash, Sorbus americana Marshall, and, to a lesser extent, the showy mountain ash, Sorbus decora (Sargent) Schneider, Larvae were also found feeding on leaves of choke cherry, Prunus virginiana Linnaeus, and Sarbaronia hvbrida (Moench) Schneider.

The mountain ashes, Sorbus 3pp., are classified in the . fam ily Rosaceae, subfamily Pomoideae, and tr ib e Pomeae. B otanists are not agreed on the generic status of Sorbus, Some workers, including

Fernald (1950), classify Sorbus. Malus (apples), and Aronia

(chokeberries) as subgenera of Pvrus. Other authors (Jones, 1939j

Roland, 1947} Gleason, 1952} Canada Dept. Northern Affairs and

National Resources, Forestry Branch. 1956) recognize Sorbus as a distinct genus. The latter treatment is followed in the present study.

All authorities agree that these genera are very closely related, Jones (1939) postulates that they had a common origin, originating by genetic change within the basic set of 17 chromosomes.

He states that hybrids are known to occur between Sorbus and Aronia.

Sorbus and Amelanchier. and between Sorbus and Pvrus. Of two natural intergeneric hybrids between Sorbus and Aronia reported from eastern

North America (Jones, 1939) > one is of interest here* Sorbaronia hvbrida. which results from a cross between Sorbus aucuparia and

11 12

Aronia arbutifolia (Linnaeus f.) Elliot. This hybrid, with leaves deeply lobed and densely pubescent beneath (Figures 7, 8, and 9), was found during the present study at Fredericton and Harcourt, New

Brunswick, and at Liverpool, Nova Scotia.

Many cases of misidentification of Sorbus species have occurred. There seems little doubt that much of this confusion has resulted from intrageneric hybridization. For example, Jones (1939) states that several horticultural varieties of the European species,

§. aucuparia. are cultivated in American gardens. Also, hybrids between an American species, S. amerlcana and S. aucuparia. known as

£• splendida Hedlund, are often cultivated.

More than 80 species of mountain ashes have been described.

The group is widely distributed throughout the Northern Hemisphere.

According to Jones (1939) one or more species of Sorbus are found in almost all parts of North America north of Mexico except the Arctic regions, the area between longitude 95° and 1029, and the southeastern part of the United States. No species are found south of latitude

32° N. In other parts of the world, representatives of the genus occur over wide areas of Europe from north to south, in North Africa, and in Asia from Siberia south to the Himalayas (Bailey, 1906;

Reyder, 194-7).

The present study is concerned with the three species in eastern North America: §. aucuparia. g. amerlcana. and g. decora.

The first two are common in the Maritime Provinces, but their Figures 7 and 8. Larvae of Pristinhora geniculata (Hartig) feeding on foliage of Sorbaronia hvbrida (Moench) Schneider.

13 H

IWCTM*'' ‘ni.'-'r

F ig u re 8 15 I i

Figure 9. Foliage of European mountain ash, Sorbua aucuparia Linnaeus (on right) and that of Sorbaronia bvbrida (Moench) Schneider. The latter is an intergeneric hybrid between S. aucuparia and Aronia arbutifolia (Linnaeus f.J Elliot. The trunks of these trees were intertwined. Fredericton, N, B. 16

occurrence is spotty and scattered and they have not been seen in

monocultures. Summaries of the distribution and characteristics of

these species are as follows*

Sorbus aucuparia Linnaeus.—This species has an extremely

wide distribution. Reyder (1947) and Bailey (1906) record it in

Europe to West .Asia and Siberia. Sargent (1894) states that a

Japanese form is common in Yezo (= Hokkaido) and on a ll the high

mountain ranges of Hondo. In North America the species has been

frequently planted as an ornamental and is locally naturalized from

Labrador to British Columbia (Canada Dept, Northern Affairs and

National Resources, Forestry Branch. 1956). Jones (1939) reports it

south to Pennsylvania, westward to North Dakota and in the state of

Washington. Gleason (1952) reports it south to the D istrict of

Columbia, and in Indiana, Illinois, and Iowa* In addition, Fernald

(1950) lists it in Alaska and in Ohio.

According to Jones (1939, p. 4)> "Sorbus aucuparia has been a cause of much misunderstanding of the North American species of mountain-ash because specimens of that distinctive European species frequently have been mistaken for the native American S. decora, or for intermediates between that species and S. amerioana . . . . " 5 further, he states that ..."Complexity is added by the possible fact th a t g . aucuparia L. is a Collective species . 1 Certainly Linnaeus 1 description of the leaves as 'utrinque glabris 1 does not desoribe very accurately most of the specimens of the plants that are currently 1 7

passing as S. aucuparia It has been suggested (United States

Dept. Agriculture, Forest Service. 1948) that climatic races of

S. aucuparia have developed in view of the wide range of the species

and the recognition of several varieties.

Jones (1939) states that the seeds are frequently carried

by birds to localities surprisingly remote from human habitations.

It is perhaps the most common of mountain ashes in the Maritime

Provinces and is the species studied most closely by the writer. The

tree grows up to 40 feet in height. It has white hairy winter buds whereas those of S. americana and S. decora are smooth and gummy.

The leaflets are small and blunt with teeth usually below the

middle (Figure 10).

Sorbus americana Marshall.—This native tree is widely distributed from the Atlantic Coast to the south end of Lake Winnipeg

in Manitoba (Canada Depb. Northern Affairs and National Resources,

Forestry Branch. 1956), south to Minnesota, Illinois, Pennsylvania, and in the mountains to North Carolina (Gleason, 1952). Roland (1947) and Fernald (1950) respectively list it as far south as Tennessee and

Georgia. Shrub-like versions of this species are common along roadsides throughout the Maritime Provinces. Characteristically it ranges from 10 to 30 feet in height and from 4 bo 10 inches in diameter. It is valued chiefly as an ornamental and because its fruit provides food for birds. It is easily distinguished from the other two species by its much more narrow lance-shaped, fine- toothed leaflets (Figure 12). Figure 10. Leaf of European mountain ash, Sorbus aucuparia Linnaeus.

Figure 11. Leaf of showy mountain ash, Sorbus decora (Sargent) Schneider. Note serrationB of leaflets are mainly apical.

Figure 12. Leaf of American mountain ash, Sorbus americana Marshall.

Figure 13. Leaf of false spiraea, Sorbarla sorbifolia (Linnaeus) Alexander Braun. Note the double serrations on the leaflets which distinguish it from Sorbus spp.

0 18 19

Figure 10 Figure 11

Figure 12 Figure 13 20

Sorbus decora (Sargent) Schneider.—Also a native to North

America, this tree is found from Newfoundland and Labrador west to

Manitoba (Canada Dept. Northern Affairs and National Resources,

Forestry Branch. 1956). It has been reported by Gleason (1952) from

Minnesota south to New York and in Iowa, Indiana, Ohio. Fernald (1950) has listed it also from southern Greenland and from Massachusetts.

It has been recorded in several areas in the Maritime Provinces

(Jones, 1939; Roland, 1947), but during the present study only one specimen was located, at Truro, Nova Scotia. The tree is usually small, ranging in height from 15 to 35 feet and in diameter from

4 to 12 inches. Like the previous species it is valued as an ornamental and its fruits provide winter food for birds. Its fruits are 8 to 10 mm. thick (compared with fruits 4 to 6 mm. thick for

§. americana) (Roland, 1947), and its leaflets are broader, with teeth chiefly above the middle (Figure ll).

Occasionally leaves of the false spiraea, Sorbaria sorbifolia (Linnaeus) Alexander Braun, are mistaken for leaves of

Sorbus spp. even though this plant does not grow to tree size. This shrub, a native of east Asia, is common along roadsides and fence rows in eastern United States and Canada (Gleason, 1952)• The leaves of §. sorbifolia (Figure 13) are remarkably similar to those of S. aucuparia but may be distinguished from the latter by the presence of double serrations on the leaflets. DISTRIBUTION

Examination of the literature, and correspondence with

entomologists in North America, Europe, and Asia, indicate that

P. geniculata has been found in all three continents from about 40° to about 56° north latitude (Figure 14). The southernmost record of

occurrence was obtained by William M. Boyd, Chief, Bureau of

Entomology, Department of Agriculture, State of New Jersey, who sub­ mitted larvae to the writer in 1959 from Lawrenceville, New Jersey.

The northernmost record of occurrence is from Silini, Latvia

(Conde, 1934).

Despite the fact that the insect has been known in Europe

since 184 Q, relatively few records of occurrence have been published.

In continental Europe the species has been recorded on S. aucuparia in Poland at Jaflchkenthale, Oliva, near Zoppot, Danzig, and Schlesien

(= Silesia); in Denmark at Sonderburg (Brischke and Zaddach, 1883); in Holland in the towns of Lonnelcer and Plasmolen (van Rossum, 1904); in Latvia at Silini (Conde, 1934); in Germany at Freienwalde (Wolff,

1924), at Brucher Lache (Lorenz and Kraus, 1957), and Dr. J. Franz^-

(private communication) said th a t i t has been found a t Bremen, near

Hamburg, and at Ettlingen. Benson (1958, p. 158) indicates that the sawfly occurs in ..."North and Central Europe to Italy...," but

^Institut fflr biologische Schfidlingsbekfimpfung, Darmstadt, Germany.

2 1 Figure 14-. Map showing locations of collections of P. geniculata in North America, Europe, and Asia. Note th a t th e known distribution of the insect ranges from about 40° to about 56° north latitude. January and July isotherms are shown in broken and continuous lines, respectively. ARCTIC OCEAN

REENLAND

EUBOP

NORTH PA a FI C OCEA N NOR TH

SOUTH PACIFIC OCEAN

F igaro 14 reference to the species in Italy has not been found in the literature or mentioned in letters from European workers. Also, no references have been found on the occurrence of the insect in

Belgium or France. The sawfly was first found in England at Lyndhurst

(Morice, 1922), and more recently at Tring, Heath, and Reach (Benson,

1958). In Ireland i t has been found in County Wicklow (Benson, 1958).

In Asia, P. geniculata was collected on the Kamchatka

Peninsula near Petropavlovsk and Elisovo, presumably on §. aucuparia

(Malaise, 1931).

The sawfly was f i r s t found in North America a t Haines F a lls,

New York, in 1926 (Schaffner, 1940)* There seems l i t t l e doubt th a t th is sawfly was introduced from Europe, probably as cocoons in earth accompanying nursery stock or as eggs on foliage. Evidence, provided in Figure 15, that the insect has spread in all directions, but mainly to the north and east, was obtained from reports of state- conducted surveys of forest insect damage, the Canadian Insect Pest

Review, Reports of the Forest Insect Survey in Canada, and from unpublished records of a large number of entomologists in the United

States and Canada. P. geniculata is now known to occur in the

United S tates in Maine, New Hampshire, Vermont, Massachusetts, New

York, Connecticut, New Jersey, Pennsylvania, and Michigan. The

insect was first recorded in Canada in southern Quebec in 1934

(Petch, 1935j Twinn, 1938). Since th a t time it s d istrib u tio n has

increased remarkably and it is now found in all eastern provinces of Canada as far west as Haviland Bay, Lake Superior, Ontario, where Figure 15. Map showing general locations and early years of collection of P. geniculata in eastern North America. Note the apparent spread of the insect in all directions from southern New York State where it was first collected on th e continent in 1926. *41

I4*

F igure 15 27 i t was located in 1958 (S ip p ell and MacDonald, 1959)* The species was first recorded in New Brunswick in 1937 (Balch, 1937); in Nova

S cotia in 1939 (Brown, 1948); in Prince Edward Island in 1941 (Brown,

1942); and in Newfoundland in 1949 (Reeks, Forbes, and Cuming, 1950).

This Is another example of an introduced insect, which with a widely distributed food supply, suitable climatic conditions, and the absence of important enemies, has become successfully established over a wide area of North America, apparently within 50 years.

Indeed, it appears that the insect is at least as common in North

America as i t i s in Europe and perhaps more so. BIOLOGI

Summary of Life History in New Brunswick

The mountain ash sawfly overwinters as a larva in a cocoon in the litter or just below the soil surface* Pupation occurs in the spring, followed by adult emergence in the latter part of June and early July. Oviposit ion takes place soon after emergence. Male larvae have four instars and feed for about two weeksj female larvae have five instars and complete their feeding in about three weeks.

The larvae drop to the ground and spin cocoons. Some individuals develop to adults and undergo a second generation in August and

September, but the majority have only one generation.

Description and Habits

Egg

The eggs are about 1.3 mm. long and 0 ,6 mm. wide, pearl gray, elliptical, slightly flattened dorsad and convex ventrad. Red eye spots and brown tips of the mandibles are visible 2 to 3 days before hatching.

The eggs are laid around the periphery of the leaflets and are Inserted between the epidermal layers through incisions made by the saw of the female (Figures 16 and 34)*

Eggs of the first generation were observed between June 10 and July 9 and those of the second generation between August 20 and

September 7 (Table l). Second generation eggs were found on both

2B 29

Figure 1 6 . Swellings on periphery of leaflets of S. aucuparia containing eggs of £. geniculata. T a b le 1

Observations on Period of Occurrence and Duration of Developmental Stages of P. geniculata. Fredericton, N. B. 1950-1954.

Period of occurrence Earliest and latest No. Length of stage - days. S tage G eneration No. o b s. dates observed days Minimum Maximum Mean

Egg 1 IS June 10 - July 9 29 6 9 8 .1 2 3 Aug. 20 - Sept. 7 18 8 13 10.3

Stage I larvae 1 2 2 1 June 28 - July 18 20 2 5 3.5 2 3 Sept. 2 - Sept. 10 8 3 6 4 .3 Stage II larvae 1 27 June 29 - July 22 23 2 5 3 .2 2 1 S e p t. 6 - S e p t. 8 2 2 — —

Stage III larvae 1 24 July 2 - July 22 20 2 5 3 .4 2 1 S e p t. 8 - Sept. 14 6 6 — —

Stage IV larvae 1 14 J u ly 6 - J u ly 29 23 3 6 4 .1 2 2 Sept. 14 - Sept. 25 1 1 ???

Stage V larvae 1 8 July 12 - Aug. 6 25 5 8 6.5 9 2 1 S e p t. 25 -- • ?? Pupa 1 6 June 6 - J u ly 3 27 8 1 2 9 .8 \ A dult 1 132 June 1 8 - J u ly 3 15 — «•_ 2 1 1 Aug. 5 - Aug. 27 22 --- — --- T a b le 2 Observations on Longevity of Caged Adults, Oviposition, Incubation, and Egg Mortality of P. geniculata. Fredericton, N. B. 1951 - 1954.

Incubation period Daily aean teap. Dates adult activity E xpt. No. and sex Eggs Dates eggs D uration deposition to dates eggs Per cen t no. of adults Emerged Caged la id Died hatched (days) of hatch la id hatched m o rta lity

51-1 ** June 18 June 18 June 21 June 2$ Cage and fo lia g e destroyed by wind — — — / - 51-2 June 18 June 18 June 20 June 25 June 28 8 62.5 __ ___ 51-3 June 18 June 18 June 20 June 25 June 29 9 62.4 ___ __ 51-5 2&0, lp — June 29 June 30 July 1-3 J u ly 9 9 64.3 114 106 7.0 51-6 266, 1$ Juno 29(p) June 29 June 30 J u ly 1-3 J u ly 9 9 64.3 87 75 13.8 51-7 *9 June 24* June 29 June JO J u ly 3 J u ly 9 9 64.3 17 11 35.3 51-8 , 1 9 June 24* June 29 June 30 July 3 July 9 9 64.3 77 37 51.9 52-1 26 6, lp June 27 June 27 June 28 -- Ju ly 5 7 66.8 — 60 52-2 June 28 June 28 June 30 — J u ly 7 7 69.4 71 30 57.7 52-3 2?? June 28 June 28 June 30 — J u ly 7 7 69.4 47+9** 42 — 52-4 *9 June 29 June 29 J u ly 1 — J u ly 7 6 70.4 47 42 10.6 53-1 2po June 17-18 June 18 June 20 — June 28 8 6 6 .4 107 46 57.0 53*2 2?? June 19-20 June 20 June 22 Juno 22 June 30 8 66.1 16 4 75.0*** 53-3 3$p ___ June 23 June 23 June 24 June 24-25 J u ly 2 8 66.6 100 40 60.0 53-5 2p9* * — June 25 June 27 -- J u ly 4 7 67.8 70 22 68.6 54-1 i ? r i 9 Aug. 18 Aug. 18 Aug. 20 Aug. 30 10 62.0 150 31 79.3 T o tal 912 546 Av. 39.5

• Living ££ retained in cold storage. ** Nine eggs mere selected for measurement and disseotiaa. *** Undetermined Heniptera nyaph seen on foliage oostaining 12 egga that ears destroyed. **** Field-oolleoted adults. 32 original and second-growth foliage, but were more common on the latter. The mean date of occurrence in each generation was June 28 and August 29. The incubation period in the first generation ranged from 6 to 9 days with a mean of 8 .1; in the second generation eggs hatched in 8 to 13 days with a mean of 10.3 (Table l). Temperature plays an important role in regulating the length of the egg stage.

Table 2 shows that eggs hatched in 6 days when the daily mean temperature from deposition to hatching was 70° F. On the other hand the duration of the egg stage ranged from 7 to 10 days at temperatures from 62° F. to 69° F. Daviault (1947b) observed that the optimum temperature for the development and successful hatching of eggs of this insect is about 22? C. (71° F.).

Single caged females laid 17 to 150 eggs with an average of

80(Table 2). The largest number of eggs was laid by a second-gener- a t ion adult th a t emerged August 18 , The numbers of oflcytes found in ovaries of six newly emerged females are lis te d in Table 3.

Table 3

Numbers of OBcytes in Six Newly Emerged Females of P. geniculata.

Specimen 1 2 3 A 5 6

Fully developed oBcytes 71 62 50 A3 42 45

Undeveloped oBcytes 111 115 116 100 140 126

Totals 182 177 166 143 182 171 33

larva

Larvae of the first three instars are pale green to yellow

with heads and thoracic legs dark brown to black. The body is

slightly more yellow in the later instars. In the fourth instar some

larvae have dark brown to black heads and thoracic legs, and some have yellow heads and pale yellow thoracic legs (Figure 17). All

larvae of the fifth instar have yellow heads and yellow thoracic legs.

Second-instar larvae have small, black spots on the thorax and abdomen. These become la rg e r and more numerous in the th ird in s ta r.

The number and size of these spots, p artic u larly on the thoracic segments, vary somewhat with individuals but their position is quite uniform. In larvae of the third, fourth, and fifth instars, spots are usually present on the dorsal aspects of the thoracic segments, the first abdominal segment, and abdominal segments 6 to 9 (Figure 17), and on the laterodorsal, supraspiracular, epipleural, and hypopleural areas of all segments except the last.

Larvae from newly hatched eggs invariably begin to feed near the eggs at the edges of the leaflets. Usually they consume all of the leaflet except the mid rib and the areas immediately adjacent to egg sites. These unchewed parts of the leaflet dry, become brown, and curl (Figures 7 and 18). Larvae of later instars typically destroy all of the leaf except the mid ribs of the leaflets and the p etio le (Figures 19 and 20). The larvae of the f i r s t two in stars 34

Figure 17. Five instars of larvae of P. geniculata. Note that head capsules of larvae in Instars 1 to 3 are nearly black. Larvae in the fourth instar have yellow and black heads (second and third from left); those with yellow heads have four instars and produce males; those with black heads w ill moult to the fifth stage and develop as females. Figure 18. Leaf of S. aucuparia partially destroyed by first- and second-instar larvae of P. geniculata. Note larvae feeding gregariously on lower leaflets.

Figure 19. Typical sawfly defoli­ ation on £. aucuparia.

Figure 20. New crop of leaves of S. aucuparia produced after almost complete defoliation by larvae of P. geniculata.

35 F igure 18 F igure 19

Figure 20 37 feed gregariously. The tendency to disperse is noticeable in the third instar, and larvae of the fourth and fifth instars often feed singly. The feeding position shown in Figure 8 is typical.

Larvae of the first generation were first observed on

June 28 and l a s t seen August 6 ; second generation larvae were

. observed from September 2 to September 25. The minimum, maximum, and mean duration in days of each instar are listed in Table 1. The average length of the feeding period of male larvae (four instars) at

Fredericton is 14..2 days; female larvae (five instars) require an average of 20.7 days to mature.

Laboratory rearings indicated that individuals that spun cocoons in the fourth stage developed to male adults and those that had five stages became females. Dissections of 54 fourth-stage larvae with black heads showed that they were all females. Dis­ sections of 56 fourth-atage larvae with yellow heads showed that 49 were males and seven were unsexed (neither testes nor ovaries observed). Because the testes are about the same size as a fat cell it seems certain that the testes were overlooked in these seven specimens. Dissections of one hundred fifth-stage larvae, collected in 1952, 1954, 1955, and 1957, showed that they were all females.

Accordingly, it is concluded that male larvae have four instars with yellow heads in the fourth and that female larvae have five instars with black heads in the fourth. This determination of sex in larvae 38 of the fourth and fifth Instars is facilitated by the fact that the instar of individuals may be reliably determined by head measure­ ment (see p. 5 5 ).

Several European workers, including Brischka and Zaddach

(1883), van Rossum (1904.), Enslin (1912-1917), and Lorenz and Kraus

(1957), have indicated that the larvae of £. eeniculata often emit an unpleasant odor, particularly when disturbed. Wolff (1924)* however, stated that he had not noticed this. No larval odor was detected in the present study.

Observations on the occurrence of diapause in this insect were limited to the examination of larvae from non-emergent cocoons that had been stored in cold storage for several months and then incubated. High overwintering mortality of larvae in cocoons and the subsequent loss of many of the remaining larvae in diapause prevented further study on this phenomenon. Daviault (1947a), however, observed that the insect is able to stay in diapause at least four years. He indicated that temperature extremes are among the factors responsible for the inception of diapause in cocooned larvae. There is little doubt that diapause enables the insect to adapt itself to different climatic regions. More information on diapause and factors relating to its inception and variation in the insect is needed far an under­ standing of its epidemiology.

Cocoons are dark brown and fibrous. The sizes of cocoons from which males and females emerged are lis te d in Table 4* 39

T able 4

S izes o f Male and Female Oocoons o f P. g eniculata

..... Males . .. Females No. Range (mm.) Mean No. Range (mm.) Mean

Length 119 5.0 - 7.0 6.4 84 8 .0 - 1 0 .0 8 .6

Width 119 2.5 - 3.0 2.9 84 3 .0 - 4.5 3.9

The examination of eleven 1-square foot samples of soil showed that about 57 per cent of cocoons were found in the top inch of soil, that about 36 per cent were found between this level and

1 inch, and that the remaining 7 per cent were located between the

1- and 2-inch levels (Table 5)*

In the present study no cocoons were observed on trees.

According to Wolff (1924)> and Lorenz and Kraus (1957), some larvae of

£. geniculata in Europe spin cocoons on the leaves, which later drop with the leaves when they fall; others drop to the ground before spinning cocoons.

Larvae of the first generation were observed to spin cocoons from July 16 to August 6 , and the mean date of cocoon spinning was July 24. van Rossum (1904) indicated that larvae were Hin the ground” by June 22; this suggests that the seasonal occurrence of the sawfly in parts of Europe is considerably earlier than that in eastern Canada.

The first phase of the prepupal larva subsequent to the T ab le 5

Classification of £. geniculata Cocoons Collected at Three Soil Levels fron Eleven One-Square Foot Quadrats. Fredericton, N. B. 1954*

Number cocoons collected Male Female No. dead No. dead S o il fron o .c. No. easreed Ho. chewed No. fron o .c. No. eaeraed _Jfo. chewed No. Grand level and intact Host Parasite Insects Mamals doubtful Total and in ta c t Host Parasite Insects Ifenmals doubtful Total to ta l

^ inch 103 97 0 28 14 75 317 42 72 0 25 32 44 215 532

1 inch 35 77 1 15 20 W 218 23 43 0 13 20 22 121 339

8 0 _6 2 inch 18 1 _2 _7 JO _46 A -J* _3 _2 _23 _69

Grand to ta l U 6 192 2 45 41 155 581 69 123 0 a 54 72 359 940

o.c. = Other causes 4 i spinning of the cocoon is the one in which the insect overwinters; larvae in this phase are characterized by a general compression of the body segments lengthwise and a withdrawal of the abdominal prolegs (Figure 21), The development of adult rudiments occurs just prior to pupation. Part of the pupal eye becomes apparent, the thoracic segments are enlarged, the body is distended and the abdominal prolegs are further reduced (Figure 22). ElieBcu (1932),

Prebble (1941), and others have used the terms eonymph and pronymph for these phases of sawfly larvae.

Puna

Following ecdysis the pupae are pale yellow with pink eyes (Figures 23 and 24). In five or six days the structures begin to harden and darken from the head and thorax posteriorly. Limited observations on larvae taken from overwintering cocoons and placed in gelatin capsules in the insectary showed that pupation occurred between June 6 and June 24. The mean daily air temperature during this period was 62.2° F. The duration of the pupal stage of indi­ viduals in these capsules varied between 8 and 12 days.

Adult

The adults are nearly black with mouthparbs and legs mostly p ale. The abdomen of males is uniform ly black but th a t of females is pale on the venter. Males are considerably smaller than females (Figure 25).

A comparison of the color pattern, median fovea, wings, Figure 21. First phase of prepupal larva subsequent to the spinning of the cocoon. Note lengthwise compression of body and withdrawal of abdominal prolegs.

Figure 22. Later phase of prepupal larva just prior to pupation. Note development of pupal eye, enlargement of mesa- and metathoracic segments, distension of body,-and further reduction of abdominal p ro le g s. Figure 23. Lateral view of pupa in process of shedding larval exuvium.

Figure 24. Ventral view of pupa in process of shedding larval exuvium. 44

Figure 25. Adults of P. geniculata on leaflets of S. aucunaria. Male on left, female on right. 45

ovipositor sheath, lance, and lancets of Canadian female adults and

one European female did not show any important differences. Since

Hartig's original description in 1840 , adults have been re-described

by Brischke and Zaddach (1883), Konow (1902), and Enslin (1912-1917).

Emergence of adults from overwintering cocoons was observed

between June 18 and July 3. The mean date of emergence of insectary-

reared adults was June 27. Adults of the second generation were

observed to emerge between August 5 and August 27# the mean emergence

date being August 17. Large numbers of adults were seen in flight

near European mountain ash trees on June 23, 1953, and on June 25

and 2 6 , 1954- Females lay eggs, with or without mating, usually

within one or two days of emergence (Table 2). All females caged on

foliage died within five days of cessation of oviposition.

Field observations showed that the female often did not

complete the incision in the leaf, or if so, did not deposit an egg.

Examination of 2,697 egg pockets showed that 569 or 21 per cent were

empty (Table 6). Similar behavior was observed by Severin and

Severin ( 1908 ) in Cimbex americana Leach.

The occurrence of two generations of P. geniculata has

been recorded in Europe, and elsewhere in North America. In Europe

two generations were observed by Brischke and Zaddach (1883),

Enslin (1912-17), Wolff (1924), and Lorenz and Kraus (1957). On this continent, Schaffner ( 1 9 3 6, 1940) mentioned the possibility of a

partial second generation, and Daviault ( 1 9 3 8 , 1943) reported two

seasonal broods throughout much of Quebec. In the latter publication, 46

T a b le 6

Observations on Field-Collected Eggs of £. geniculata in 1955, 1957, and 1958 at Fredericton, N. B.

No. No. No. eggs with No. o v i- 3bs. normal parasitized evidence of p o sitio n no. ©ggs .eggs predator attack scars Tota]

1 139 0 4 34 177 2 41 0 0 10 51 3 135 0 0 45(3) 180 4 92 0 0 38(13) 130 5 145 13 0 17(9) 175 6 147 0 0 3 150 7 43 0 0 24(18) 67 8 113 15 0 10(2) 138 9 76 0 1 20(13) 97 10 129 1 0 170 11 138 0 1* i s 146 12 7 0 0 4* 1 (1) 75 13 155 0 0 11(6) 166 14 145 0 2* 54(44) 201 15 42 1 14+2* 26(25) 85 16 68 3 1* 53(46) 125 17 34 0 55* 16(3) 105 18+ 53 83 1* 4 2 (8 ) 179 19 33 6 0 0 39 20 6 11 35 67(45) 119 21 0 0 0 21(1) 21 22 0 0 0 8 8 23 70 0 1* 22 93 T otal 1874 133 121 569 2697

Per cent parasitized eggs based on total eggs laid = 6.2 Per cent eggs with evidence of predator attack =5*7 + September collection * Egg pocket darkened-contents shriveled as if sucked by insects. () Figures in parentheses indicate instances in nhich a full egg receptacle was not formed. In most of these cases partial incisions between the epidermal layers of the leaflet were evident, causing the tissue to brown* 47

Daviault stated that the second generation is very weak if the

climate is unfavorable during the developmental period of eggs and

larvae of the first generation; also, he indicated that the insect

has only one generation per year in the most northern areas of its

occurrence.

Frass Studies

The daily frass drop, collected on a 2* x 2' cotton-bottom

tray placed under the crown of a moderately infested European

mountain ash tree from June 30 to August 3, is shown in Table 7; the

mean daily temperature and daily rainfall are also recorded. Most

feeding, as indicated by daily frass volumes of one or more cubic

centimetres, occurred from June 30 to July 18. This range is close to the average female larval period of 20.7 days recorded in the

field and in the insectary. The apparent effect of temperature on

feeding and frass drop was demonstrated on July 12 and July 18 when the volumes of frass increased with increases in mean temperatures to 75° P. and 71.5° F., respectively. No conclusions of the effects

of rainfall on frass drop during this period can be made.

Because of high mortality of individually reared larvae in

the insectary, frass yield studies were lim ited to five male and three female larvae. Also, high mortality of first-instar larvae

prevented an accurate assessment of frass yield in this instar. The

average frass yields, expressed in weight and numbers of pellets T a b le 7

Frass Drop of P. geniculata Collected on a 2* x 21 Square. Fredericton, N. B. 1950.

Volume fra s s Mean tem­ R a in fa ll Volume fra s s Mean tem­ R a in fa ll Date dropped (c.c.) p eratu re (inches) Date dropped (c.c.) p eratu re (inches)

June 30 1.0 66.0 0 J u ly 18 2.2 71.5 0.20 J u ly 1 1.8 58.5 0.05 J u ly 19 0.85 69.5 0 J u ly 2 3.6 66.5 0 Ju ly 20 0 .5 62.0 0 J u ly 3 3.1# 63.0 0.43 Ju ly 21 0 .4 58.0 0 J u ly 4 9.2 65.0 0.03 Ju ly 22 0.15 58.5 0.01 J u ly 5 5.4 67.5 0.02 Ju ly 23 0 .1 62.0 0 J u ly 6 — 60.0 0.89 Ju ly 24 0 .1 63.0 0 J u ly 7 5.0 67.0 0.20 July 25 0.2 57.0 0.09 J u ly 8 5.4 66.5 Trace July 26 0.1 63.5 0 J u ly 9 5 .4 62.5 0 Ju ly 27 0.1 71.0 0 J u ly ID 5 .6 65.0 0 Ju ly 28 0 .1 66.5 0 J u ly 11 5.8 69.5 0 Ju ly 29 0 .3 69.5 0.47 J u ly 12 6.0 75.0 0 Ju ly 30 0.05 68.5 0 .0 4 J u ly 13 5.4 76.0 0 Ju ly 31 0.03 67.5 0.05 J u ly U 4.0 68.5 0.01 August 1 0.01 66.0 0.46 J u ly 15 2.9 60.5 0 August 2 0.01 59.5 0 J u ly 16 1 .4 64.0 0 August 3 0.01 68.0 0 J u ly 17 1.15 61.5 0

* Accident occurred in "which volume graduate was broken. Some of the frass was lost. 49 ejected, are shown in Table 8, in relation to the average length of development of these individuals and 8 7 others of the first gener­ ation. Because of the small quantities of frass yielded in insectary rearin g s i t was necessary to use weight ra th e r than volume in i t s measurement.

Morris (1949a), in studies of the European spruce sawfly,

Diprion hercynlae (Hartig), showed that there was a close relationship between the percentage of spruce needles consumed in each instar and the corresponding percentage of frass by weight. A close relation­ ship between frass drop and foliage consumption exists also with other defoliators (cited by Morris). This aspect was not studied in the present work, but it is presumed that the same relationship holds for P. geniculata. Table 8 shows that the average weight of frass ejected by female larvae was almost three times that of males. Male larvae dropped about 75 per cent of their frass in the last instar, female larvae about 77 per cent. Correspondingly high proportions have been found in other insects, such as 78,9 per cent for

D. hercvniae (Morris, 1949a) and 8 2 per cent for d is s tr ia Hbn. (Hodson, 1941)*

Morris (1949a) demonstrated that the average weight of frass ejected in successive instars of D. hercvniae increases in rapid progression? also, he compared these absolute weights with the number of days required for the development of the corresponding instars, showing that the average rate of yield per day increased with each instar. Table 8 shows that both these observations hold T a b le 8

Frass Yield and Length of Develojaerrt In Instars 2 to 5 of £. gyr^tgiii«ta.

Male larrae______TN.—1* Frmaa elected_____ Frass ejected_____ Estifid------ih ih it m — Wo. pellets ejected win™"” Ho. pellets ejected Mftl? IftTTM fftBftl* 1WTM Instar Mean Range Per cent Mean Range Per cent Mean Range Par oent Mean Range Par cent Days Per cent Days Per cant

1 —— —--— — — — — — — — 3 .5 2 4 .7 3 .5 1 6 .9

2 3 .8 2I 5- 5.6 5 .4 211 154-241 26 .1 3 .0 1 .8 - 3 .6 1 .6 216 202-226 23 .9 3 .2 2 2.5 3 .2 1 5 .5

3 1 4 .2 9 .8 -2 0 .0 20 .0 231 157-352 2 8 .6 7 .0 5 .9 -8 .8 3 .6 125 107-142 1 3 .8 3 .4 2 3 .9 3 .4 1 6 .4

4 5 2 .9 4 3 .8 -7 1 .7 7 4 .6 365 283-433 4 5 .3 33.8 2 4 .6 -4 0 .0 1 7 .4 193 152-220 2 1 .4 4 .1 2 8 .9 4 .1 19 .8

5 — — — — — — 150.3 127.3-171.8 77 .4 369 321-4D1 4 0 .9 *ae — 6 .5 3 1 .4

_ — T o ta l 7 0 .9 10 0 .0 807 100.0 194.1 100.0 903 100.0 1 4 .2 100.0 2 0 .7 100.0 51

for P. geniculata. In the latter case, the average frass yield in

milligrams per day for male larvae in the second, third, and fourth

instars was 1.2, 4*2, and 12.9. Corresponding rates of yield for

female larvae from the second to the fifth instar were 0.9, 2.1, 8.2,

and 23.1. The average number of pellets ejected, however, does not

increase progressively with each inBtar, and, as in J). hercvniae.

seems to be more closely related to length of the instar.

The mean daily air temperature during the period was 67° F. with a maximum of 93^ F. and a minimum of 45° F. The effect of temperature fluctuations on frass yield, however, was not studied.

Morris* studies suggested that absolute frass yield is constant within ordinary temperature ranges. He cited the work of others who

showed that the rate of yield, however, is closely associated with

fluctuating temperatures. It is evident, therefore, that temperature

must be considered in intensive studies on frass yield.

Sex Ratio and Reproduction

Of 635 adults reared, 134 were males and 501 were females.

This suggests a sex ratio of 21 per cent males and 79 per cent

females. Raizenne (1957) found a ratio of 34 per cent males and 66

per cent females in Ontario.

Females were frequently observed to oviposit parthenoge-

netically, or without being fertilized (Table 2). Observations on the progeny of these females showed that they had four larval instars 52 and developed Into males. This indicates that parthenogenesis in

P. geniculata is facultative or arrhenotokous, a conclusion that was also reached by Wolff (1924) and Benson (1950). Mating was not observed in the present study.

There is p ro b a b ly considerable variation in the proportion of sexes from year to year. Far example, if males predominated in a generation, more females would be fertilized, resulting in increased numbers of females in the next generation. Because of this pre­ ponderance of females many would probably be unmated and so produce an abundance of males in the following brood. Such oscillations in sex ratio were observed by Miles (1932) in Nematus ribesii Scop.

Factors which might effect the regularity of such oscillations in

P. geniculata are the tendency of females to oviposit soon after emergence without being impregnated, and the possibility of a sex difference of specimens entering and remaining in diapause. LARVAL HEAD WIDTHS

Studies of growth in immature insects are often based on the long-established generalization that sclerotized parts do not change in size within a stadium but increase on ly at ecdysis. Dyar

(1890) was one of the first to demonstrate that widths of larval heads constituted convenient measurements of growth between different larval stages. His conclusion from measuring the head widths of 28 species of Lepidoptera during each in3tar of their development that

"the widths of the head of a larva in its successive stages follow a regular geometrical progression" has become well known as Dyar’s rule or Dyar’s law. This rule has been used as a tool by many workers as a check on the number of in sta rs observed, and to deduce from the ratio of widths in two successive instars the number of stages of inaccessible larvae or the number of ecdysea where series of cast skins are incomplete. The rule has proved useful in many lepi- dopterous larvae but in other caterpillars the ratios of increase between instars have been inconstant. Indeed, Gaines and Campbell

(1935) reported from a study of over 800 growth ratios by various investigators of lepidopterous larvae that growth ratios tend to decrease during larval development. Studies by Peterson and

Haeussler (1928) on the oriental fruit moth, Grapholitha fcsLaapeyresia) molesta (Busck), and by Brindley (1930) on the Mediterranean flour moth, Anagasta (= Enhestia) kflhniella (Zeller) show that the

53 application of Dyar’s law may indicate instars that do not exist.

The literature contains numerous instances where growth and the number of instars are directly influenced by environmental factors such as nutrition and temperature, and Dyar's rule cannot be used for corroborating the number of instars.

The application of Dyar’s rule to sawfly larvae has been considered by Miles (1931), Taylor (1931), Friend (1933), and

Ghent (1956). The two former authors observed that Dyar's rule is useful if applied to the feeding instars, but does not hold for the non-feeding prepupal stadium, where larvae show no increase in head width beyond that of the last feeding instar. Friend (1933), working with Fenusa pusilla (Lep.) (= pumila Klug.), stated that geometrically progressive increases did not regularly occur in successive larval instars of this species. Ghent (1956), however, who re-examined

Friend’s data, showed that growth of the head capsule of £. pusilla and that of Neodinrion americanus banksianae Roh. was almost precisely linear and that a straight line more accurately describes the growth than the exponential curve described by Dyar’s rule.

Moreover, Ghent presents evidence which shows that Dyar's rule is not reliable as a check on missing instars.

In the present study larval head capsules were measured to check on the number of feeding instars, to determine the relationship of sex to head widths, to see if the increase in head widths in successive instars followed a linear or an exponential growth pattern, 55 and to calculate theoretical growth rates by several methods and to compare the goodness of fit of these calculated progressions with the observed progression.

The larvae for this study were randomly collected in 1954 at two- or three-day intervals from foliage of S. aucunaria at

Fredericton, N. B. All larvae were killed in 95 per cent alcohol and preserved in 75 per cent alcohol. Head capsule widths were measured with an adjustable ocular eyepiece attached to a binocular microscope.

Head widths of first- and second-stage larvae were measured accurately to 0.03 mm. and interpolated to 0.003 mm. Third- and fourth-stage individuals were measured accurately to 0.05 mm. and interpolated to

0.005 mm. Fifth-stage larvae were measured accurately to 0.13 ram. and interpolated to 0.01 mm.

When the values for 451 head widths were presented as frequency distributions in units of 0.01 mm., the measurements fell into five well-defined, discontinuous groups, which, in addition to the general appearance of the larvae, showed that there are five feeding instars (Figure 26). McGugan (1954) observed that sex differences and the effect of parasitism caused considerable variation in head capsule size within an instar of the spruce budworm. In the present study larval parasitism was negligible. A slight bi-mo dal pattern in some of the groups suggested a difference in head width due to sex. Accordingly, 110 fourth-instar larvae were sexed by dissection and examination of the gonads. Fifty-four of these were females and 56 were males. The mean head width of the Figure 26. Frequency distribution of larval head capsule widths of P. geniculate.

56 NUMBER OF LARVAE 40 - 1 i-i 4 . 5 .0 6 .0 80 .5 9 LO 0 LO 5 2 15 .0 .5 .0 .5 5 15 .0 .5 7 17 t80 165 0 t.8 1.75 L70 1.65 1.60 155 150 1.45 1.40 1.35 1.30 125 L20 U5 LiO 105 LOO .95 0 3 .85 0 .8 5 7 .70 .65 .60 .55 0 .5 .45 ------1 ------1 ------1 ------1 ------1 ------i 1 ------1 ------1 ------1 ------ED IT (mm.) WIDTH HEAD r i r 1 gr 26 igure F ------i 1 ------1 ------1 ------1 ------1 ------1 ------1 ----- ~i ------i 1 ------1 ------i ------r 58 females was 1.441 non. as compared with 1.373 mm. for the males. This difference was analyzed by the following formulae. The resultant nt B value of 10,30 showed the probability of a real difference to be approximately 0,999.

where = mean of female head widths

*2 = mean of male head widths

= number of females

Ng = number of males

standard error of the mean difference

D.F. = 108

No attempt was made to sex larvae in the early instars.

Dissecti on and sex determination of 100 larvae, classified as fifth instar on the basis of head width, taken from four col­ lections in 1952, two collections in 1954» two collections in 1955, and one collection in 1957, showed that they were all females. This information supports that obtained in individual roarings and indi­

cates that male larvae have four feeding instars and female larvae have five such instars. 59

The numbers of larvae from which head measurements were taken and the mean head widths of each instar in millimetres are

shown in Table 9* Appendix Table 1 shows that the range of head sizes

in instars 1, 2, and 3 is considerably smaller than that in the fourth

i n s t a r .

Because there is no overlapping in head sizes between

instars and because the intervals between the extremes of each group are relatively large, it seems apparent that the instar of single

individuals may be reliably determined in the absence of serious

nutritional or environmental effects. No attempt was made to determine

if variation in the number of instars occurred under varying con­

ditions of food or environment.

Ghent (1956) has pointed out that linear growth in width of head capsules is determined by the addition of a constant amount to the width of the head at every moult. The difference between the

successive means in the present series were as follows: 0.19 mm.,

0 .3 4 mm., 0 .3 8 mm., and 0.38 mm. Although th e re i s f a i r l y uniform

linearity between the means of the head widths of instars two to five, the difference between the means of the first and second

instars is only about half the amount of the differences between the

successive means. This indicates that the growth of head capsules

in the specimens measured tends to be curvilinear rather than

strictly linear (Figure 27). However, it is quite possible that if T a b le 9

Conparioon of Obaerved Hoad Capsule Widths of Larrae of £. with those Calculated by Scran Methods.

Q > aerred L o g ar- Beau At . ith w io No. widtha ■ D yar'a* grow th grow th .Linear regression equations Parabolic equations s t a r ■assured (m .) r a t i o D if f . r a t i o D if f . r a t i o D if f . X=**bx D iff. Log I»e+bx D iff. I= a + h rfc r^ D iff. Log YBa+brfflje* D if f .

1 ■ 101 0 .4 9 3 — — — — — — 0 .4 2 9 0 .0 6 4 0 .5 0 2 0 .0 0 9 0 .4 8 0 0 .0 1 3 0 .5 1 9 0 .0 2 6

2 74 0 .6 8 4 0 .6 8 4 0 .0 0 .6 8 1 0 .0 0 3 0 .6 6 0 0 .0 0 4 0 .7 5 4 0 .0 7 0 0 .7 0 2 0 .0 1 8 0 .7 2 2 0 .0 3 8 0 .6 8 7 0 .0 0 3

3 104 1.029 0.949 0 .0 8 0 0 .9 4 1 0 .0 8 8 0 .9 3 8 0 .0 9 1 1 .0 7 9 0 .0 5 0 0 .9 8 0 0 .0 4 9 1 .0 2 4 0 .0 0 5 0 .9 4 6 0 .0 8 3

4 110 1 .4 0 6 1 .3 1 6 0.090 1.300 0.106 1 .2 9 4 0 .1 1 2 1 .4 0 4 0 .0 0 2 1 .3 7 0 0 .0 3 6 1 .3 8 6 0 .0 2 0 1 .3 5 4 0 .0 5 2

5 62 1 .7 8 8 1 .8 2 5 0 .0 3 7 1 .7 9 7 0 .0 0 9 1 .7 8 6 0 .0 0 2 1 .7 2 8 0 .0 6 0 1 .9 1 4 0 .1 2 6 1 .8 0 7 0 .0 1 9 2 .0 1 5 0 .2 2 7

Weighted euwa of equarea of differ- l.&a 2.047 2.242 1.260 1.409 0.193 4.278 enoss bet wan actual and oalculatad weans Figure 27. Comparison of observed mean head capsule widths of larvae of P. geniculata and those calculated by seven theoretical progressions. HEAD WIDTH (mm.) 2.00 1.70 1.40 1.60 ISO 1.50 1.00 1.30 1.10 1.20 .80 .90 .50 .60 .70 2 //// S traight line equation, equation, line ratio growth traight S ic Logarithm Parabolic equation, y» y» equation, Parabolic Dyar's ratio ratio Dyar's Observed vrg got rto ratio growth Average " , log " " " iue 27 Figure 2 6 INSTAR 3 logy*a+bx+cx2 , o+bx+cx2 y>atbx y>atbx « y ////// a + + a bx 4 5 the head sizes of larvae of each sex were analyzed separately and greater numbers of specimens were measured, a somewhat different growth pattern might be demonstrated.

Seven methods of calculating theoretical growth ratios from the observed measurements were tested;

1. *Dvar!a ratio.—Dvar (1890) used the ratio obtained by dividing the head width of an instar by that of the succeeding instar. However, in recent years the reciprocal of this ratio has been widely used because it indicates growth directly; in the present study this ratio of increase was determined by dividing the mean observed head width of first-instar larvae into that of second-instar larvae. Calculated means of subsequent instars were obtained by using this ratio with the observed mean of the first in s ta r .

2. Average growth ratio.—An average ratio of increment was obtained by dividing the observed mean head width of each instar by the one that precedes it. As above, the calculated progression was obtained from this ratio and the observed mean of the first in s ta r .

3. Logarithmic growth ratio.—A growth ratio involving logarithms was calculated by the following formula, from which 64

Lejeune (1950) obtained rather satisfactory results.

lo g R = S M

where: R = growth ratio

L s average head capsule width of the last instar

S = average head capsule width of the first instar

M = number of moults between 1 and S

As pointed out by Lejeune this method is simple and requires the average head widths of only the first and last stadia.

However, the number of intervening moults must be known.

4* Linear regression equation y ss a + bx.—Calculated means for each instar were obtained by substituting for x in the least squares regression equation where y = mean width, x = stadium.

5* Regression equation log y = a + bx. --Calculated means for each instar were obtained by the same method outlined in (4) except that the observed mean widths were converted to logarithms far calculation and the resulting logarithmic widths were transposed to arithmetic numbers.

6. Parabolic equation v = a + bx + ex?.—As in (4) and

(5), y equals the actual mean width of each instar and x the number of the instar. After calculating the constants a, b, and c, values for each instar were determined by substituting for x in the eq u atio n . 65

7. Equation log y = a + bx + ca?.—Values for each instar were determined by the same method as in (6) and the calculated logarithmic widths transposed to the arithmetic scale.

The values calculated by each of the above-mentioned methods were compared with the observed values graphically (Figure 27) and by computing the weighted sums of squares of the differences between the actual and the calculated means (Table 9)* A small sum represents a good fit.

The weighted sums of squares of the differences between the actual means and those calculated by "Dyar's" ratio, the average growth ratio, and the logarithmic growth ratio were 1.641, 2,047, and

2.242 for each of these methods, respectively (Table 9). This indicates that the deviations from the observed values were slightly smaller in the application of "Dyar's" ratio than in the other two methods.

The calculated values obtained for each instar by fitting the straight line equation y = a + boc to the observed means are also shown in Table 9. The sum of the squared deviations of the calcu­ lated widths from the actual widths is 1.260, which is less than that obtained in applying "Dyer's" ratio, the average growth ratio, and the logarithmic growth ratio, and indicates closer agreement with the observed values (Figure 27). Gaines and Campbell (1935) and

Ludwig and Abercrombie (1940) indicated that if the increase in size of the head capsule follows a regular geometric progression, the relationship may be best represented by the equation log y = a + bx. 6 6

Application of this equation to the observed widths produced

calculated widths of which the sun of the squared deviations from

the actual widths was 1.409. This indicates that the use of

logarithms in this way produced calculated values more discrepant

from those observed than the equation y = a + bx.

As mentioned earlier (p. 53), several workers with lepi- dopterous larvae have reported growth ratios which are high in the early part of larval development and diminish somewhat during develop­ ment. Gaines and Campbell (1935) in studying the corn ear worm,

HeliothiB zea (Boddie) (= obsoleta (Fabricius)), obtained such a pro­ gression. They showed that the relationship between head width and stage of development could more accurately be described by the second degree equation log y = a + bx + c y ? than by the equation log y = a + bx. The following growth ratios between successive instars of

P. geniculata were obtained: 1.39, 1.50, 1.37, and 1.27. As these ratios show some tendency to decrease in the late stages, the appli­ cation of the parabolic equation y = a + bx + ex? and the. equation log y = a + bx + cx2 to the observed widths was tested. The weighted sums of squares of the differences between the actual means and those calculated by these two equations was 0.193 and 4*276, respectively

(Table 9) * The agreement between the observed means and the means calculated by the parabolic equation y = a + bx + cx^ is closer than in any of the other methods tested. This indicates that the 67 increase in size of the head capsules selected for measurement does not follow a regular geometric progression, but agrees more closely with a relationship demonstrated by a parabola. This appears to be the first time that a parabolic equation has been applied to head capsule growth in sawflies. HC6T RELATIONSHIPS

Effect of Insect on Host

Growth of Host

A knowledge of the growth characteristics of a tree species is requisite to any analysis of the effects of insect defoliation or other factors affecting tree growth. Nothing has been seen in the literature nor has the writer observed any mortality of mountain ash trees that could be attributed to the effects of defoliation by the

sawfly, even though some trees bear repeated defoliation from year to year. It was felt that some information on the growth pattern of £. aucunaria trees and its relationship to the development and feeding habits of the insect might help to explain this. Accordingly, the radial increment was measured and shoot growth observed on two trees in Fredericton in 1955. Radial measurements were taken weekly from April 29 to September 30 with a dendrometer. Two points, one on the north and one on the south side of each tree at breast height were selected for measurement. Simultaneously, the growth of four terminal shoots at the cardinal points on each tree was measured to the nearest millimeter; following the technique used by Morris,

Webb, and Bennett (1956), the base of the bud was used as the reference point throughout the season. Sawfly defoliation proved to be negligible on Tree 1 and light to moderate on Tree 2.

63 69

The relation between radial growth and mean weekly temperatures of the air and ground (l inch below the surface) is shown in Figure 28.

Radial increment is expressed cumulatively in Table 10.

Growth commenced about May 1 and was terminated ly September 23 on both tre e s . Radial growth was about 50 per cent complete on

July 7. Although radial and shoot growth commenced at or near the same time, shoot growth was virtually complete when cumulative radial growth was at the 50 per cent point.

Food consumption of the mountain ash sawfly is greatest in the later instars. Generally larvae are in the fourth and fifth instars between July 6 and August 6 (Table l) . At this time trees have completed 50 to 75 per cent of their radial growth and almost all of their shoot growth. Therefore, it is not surprising that the trees withstand considerable defoliation with apparently little effect. In this connection, Mr. J. Clark^* (private communication) showed that all beech trees that were artificially defoliated early in the growing season for three years were either dead or dying by the third year, whereas no mortality occurred in similar trees that were defoliated after mid-July. He postulates that foliage is produced at the expense of food reserve and when defoliation occurs early in the season there is no opportunity to replace the carbo­ hydrates through photosynthesis. On the other hand the loss of

■^Tree Ihysiologist, Forest Biology Laboratory, Fredericton, N. B. Mean Radial Growth in Inches Mean Weekly Temperatures - Deg. Fahr. .010 .020 .030 o nd T« i r u t o r t ip I i r « T u f o « p d n im T ro G ir A *— temperatures of the a ir and the ground ( l inch inch l ( ground the and ir a the of temperatures eo te urae. rdrco, . . 1955. B. N. Fredericton, weekly rface). mean su to the s e below tre aucunaria S. two of Figure 28. R elationship of ra d ia l growth growth l ia d ra of elationship R 28. Figure ueJuly June K x r T l 70 uutSpe ber Septem August 71

T able 10

Radial Growth of Two S. aucuparia Trees Based on Dendrometer Readings on the North and South Sides of Each Tree at D.B.H, Fredericton, N. B. 1955*

'M '' " Tree & Tree p , Av. aocumu- Av. accumu­ lated growth, Per cent lated growth, Per cent Date Inches _____ development inches development

A pril 29 m m — — May 6 .004 1.9 .002 1.1 May 13 .008 3.8 .003 1.6 May 20 .013 6.2 .007 3.8 May 27 .023 10.9 .016 8.7 June 3 .033 15.6 .025 13.6 June 10 .042 19.9 .033 17.9 June 16 .052 24.6 .043 23.4 June 24 .071 33.6 .062 33.7 June 30 .086 40.8 .075 40.8 July 7 .108 51.2 .092 50.0 July 17 .133 63.0 .111 60.3 July 22 •144 68.2 .119 64.7 July 28 .158 74.9 .130 70.6 August 5 .165 78.2 .135 73.4 August 11 .177 83.9 .145 78.8 August 19 .188 89.0 .158 85.9 August 26 .199 94.3 .168 91.3 Sept. 2 .206 97.6 .176 95.6 Sept. 9 .208 98.6 .181 98.4 Sept. 16 .211 100.0 .182 98.9 Sept. 23 .211 .184 100.0 Sept. 30 .211 .184 72

leaves later in the season permits at least partial replacement of

the food reserve and hence the effects of defoliation are less

severe. Another factor which may contribute to the capacity of

§. aucuparla to withstand considerable foliage loss is the feeding

pattern of the sawfly, which causes greater defoliation in the lower

crown levels than near the tops of the tree (see p. 92).

Defoliation and Kefoliation

Many of the severely defoliated shoots of §• aucuparla

grow a second crop of leaves (Table 11; Figures 20, 29, and 30).

Other species of broad-leaved trees in eastern North Amerioa that

produce a second crop of leaves following severe defoliation by

insects or climatic agencies include white elm, Ulmus americana

Linnaeus (Balch, 1939ai red oak, Quercus rubra Linnaeus (Cuming,

195#), trembling aspen, PqpuI ub tremuloides Michaux (Rose, 195#),

and beech. Faeus grandlfolia Birhart (Clark, private communication).

In the present work, defoliation estimates were made on

original and second-growth foliage on 40 apical shoots of

§. aucuparla: the lengths of shoots were measured and the numbers of

leaves and leaflets on defoliated and refoliated leaf clusters were

counted (Table 11). An analysis of these observations is as follows:

(a) Second-growth leaves usually arose from buds in the axils

of the petioles of defoliated leaves (Figure 20), and the shoots

showed little or no tendency to elongate when new foliage appeared. 73

T ab id 11

Obeervatione on Defoliation and Refoliation of Apical Leaf Cluatera of European Mountain Ash Following Attache tiy £• geninni«t«_ Fredericton, II. B.

Length of atan of Ueafluronente on original and aeooad-arowth foliage Prwofa iw f aliirttr la ■■ No. of No. o f Av. no. le a f- Eatlastad defol­ ? # rt.+ vith with l a m a le a fla ta iation (car ofltrt) axmn arlg. seoond Qrlg. ! 1 Qrlg. Saoood Qrig. Seoond Orlg. Seoond ft). 1 m l Exp. f o l. g r. f o l. Growth growth growth growth growth growth growth growth 1954 1 A B 202 202 0 9 5 114 60 12.7 12.0 95 0 2 B S 47 47 0 6 1 72 11 12.0 U.O 100 0 3 C E A A 0 6 3 73 42 12.2 14.0 100 0 A D E 62 62 0 5 3 TO 40 14.0 13.3 98 0 5 0 S 18 18 0 5 3 60 38 12.0 12.7 100 0 6 0 V 175 177 2 7 0 A -- 11.6 — 0 — 7 D E 20 20 0 6 0 69 — 11.5 — 80 — 3 D T 345 345 0 8 0 106 — 13.2 99 — 9 D E 20 20 0 5 0 67 — 13.4 -e* TO 10 G N 28 28 0 5 3 61 39 12.2 13*0 90 0 11 DB 19 19 0 1 0 11 0 11.0 100 — 12 D N 444 455 11 9 1* 139 7 15.4 100 — 13 D 3 223 223 e 9 0 116 0 12.9 — Traoa — U D 3 204 204 0 9 0 1 1 6 0 12.9 — 15 — 15 D 3 270 270 0 7 1 89 9 12.7 9.0 90 0 16 D 3 193 193 0 8 2 98 247 12.2 - - 100 — m . 17 DS 210 210 0 10 4 113 51 U .3 12.3 90 0 18 0 T .. — — 24 1 4 270 149 11.2 10.6 95 0 19 D V 400 400 0 12 4 122 55 10.2 13.8 95 0 20 A H 490 490 0 19 14 227 140 11.9 10.0 90 0 21 DN 560 560 0 22 0 287 .. 13.0 — 80 — 22 D E 350 350 0 13 5 153 57 U .3 U .4 90 0 23 D E 172 172 0 8 4 90 47 11.2 U .8 85 10 24 DE 335 ... 335 0 17 0 194 — U .4 — 45 — 25 D 3 262}** 262) a e 0 0 — 12.1 — 30 277) 277) 13 157 2 6 0 f 204 204 0 9 2 88 14 9 .3 7.0 50 0 27 D T 363 363 0 13 5 153 £0 11.8 12.0 100 0 28 0 V 343 343 0 13 8 130 105 10.0 13.1 95 30 29 D T 265 265 0 10 0 116 — U .6 «MW 5 — 30 D E 285 285 0 9 3 128 37 14.2 12.3 95 0 A D M 387 387 0 17 4 208 44 12.2 11.0 100 0 32 D H 166 166 0 2 0 — — .. — 15 — 33 D N 200 200 0 13 0 141 ~ 10.6 — 55 -- 34 D N 330 330 0 14 0 175 — 12.5 -** 100 — 35 D I 237 237 0 17 4 184 A 10.8 7.8 100 0 36 0 I 155 155 0 8 0 96 ~ 12.0 — 100 -- 37 D 1 178 178 0 10 1 118 9 U .8 9.0 95 0 38 D R 147 147 0 7 1* 76 7 10.3 — 95 — 13.0 0 39 D H 43 43 0 8 3 105 39 13.1 95 46 0 3 315 315 0 _ 8 _ 9 105 137 13.1 15.2 100 0 T otala and average* 401 107 4778 1238 U .9 n . 6

+ Top to bottoa # Expanding tad ** Forked taoot Figure 29. Complete defoliation of small S. aucuuaria tree caused by larvae of P. geniculata. Photographed August 5, 1958.

Figure 30. Refoliation of same tree. Photographed August 26, 1958.

76

(b) Fewer leaves were produced In the second crop than In the

first crop of foliage, but there was little difference in the number

. of leaflets per leaf, which averaged 11.9 and 11.6 on original and

second-growth leaves, respectively.

(c) Defoliation of second-growth foliage by larvae of the

second generation was generally negligible; this agrees with other

observations indicating that larvae of the second generation are not

numerous enough to cause serious defoliation.

(d) Second-growth foliage was produced on 24 out of 30 shoots

on which defoliation of leaf clusters averaged 80 per cent or more;

of the remaining 10 shoots, on which defoliation waB less than 80

per cent, only one produced seoond-growth foliage (average defoli­

ation of leaf clusters was 50 per cent). This suggests some

relationship between the degree of defoliation and refoliation.

Effect of Host on Insect

Flowering in balsam fir, AbieB balsamea (Linnaeus) Miller,

has been shown to have an important effect on foliage production

(Morris, 1951a), and on the abundance and survival of the spruce

budworm (Blais, 1952; Prebble and Morris, 1951)* Because of the

possibility that flowering in £• aucunaria trees might have some

relationship to certain biological aspects of the sawfly, counts

were made of leaves on flowering and non-flowering leaf clusters and

data were obtained on distribution of flowers in tree crowns

(Table 12). T a b le 1 2 Distribution and Numbers of Flowering and Non-flowering Leaf Clusters with Corresponding Leaf Counts by Crown Level (A, B, C, D, from top to bottom), Crown Quadrant (H, B, 8, W), and Radial Distance (Outer and Inner Crown) on Four European Mountain Ash Trees. Fredericton, N. B., 1955. s s c ------Qiter grgwn______Inner crown______Flower-bearing Non flower-bearing Flower-bearing Non flower-bearing loaf-dusters leaf dusters leaf clusters leaf dusters 3. ll bSfiZSfi Leaves. No. leaf Leaves Leaves Lusti Av.no.per Av.no.per clusters Av.no.per Av.no.per r a n rli Nm&er Total cluster Number Total cluster examined Number Total cluster Number Total cluster

32 11 47 4.3 21 97 4.6 32 23 88 3.8 9 26 2.9 i 32 9 40 4.4 23 110 4.8 32 15 59 3.9 17 53 3.1 32 12 53 4.4 20 112 5.6 32 18 67 3.7 H 42 3.0 -22 14 _ & 4.4 12 _§i 4*1 -22 20 -26 h i IS -22 2*2 128 AS 201 4.4 82 400 4.9 128 76 288 3.8 52 160 3.1 32 16 71 4.4 16 63 3.9 32 19 71 3.7 13 40 3.1 32 11 44 4.0 21 88 4.2 32 15 53 3.5 17 49 2.9 3 2 U 56 4.0 18 86 4.8 32 19 71 3.7 13 45 3.5 -22 ID -62 A il 22 112 2*4 -22 l£ _£8 2j£ 16 -62 2*1 128 51 218 4.3 77 356 4.6 128 69 253 3.7 59 183 3.1 32 13 56 4.3 19 59 3.1 32 13 43 3.3 19 59 3.1 32 11 42 3.8 21 72 3.4 32 15 54 3.6 17 48 2.8 32 17 68 4.0 15 58 3.9 32 18 69 3.8 14 42 3.0 -22 n _62 h i 21 81 M -22 18 _Z2 4*1 14 -22 2.8 128 52 209 4.0 76 270 3.6 128 64 239 3.7 64 188 2.9 32 8 29 3.6 24 84 3.5 32 9 35 3.9 23 67 2.9 32 10 38 3.8 22 70 3.2 32 7 27 3.8 25 82 3.3 32 13 50 3.8 19 65 3.4 32 5 18 3.6 27 83 3.1 -22 -60 4.4 21 121 4.6 -22 -Z -26 h i -22 _Zg 2*1 128 40 157 3.9 88 324 3.7 128 28 106 3.8 100 310 3.1

512 189 785 4.2 323 1350 4.2 512 237 886 3.7 275 841 3.0 78

The average number of leaves on flowering and on non­ flowering shoots in the outer crown from all levels, all quadrants, and all trees was 4*2 and 4*2, respectively. Corresponding averages in the inner crown were 3.7 and 3.0.

An analysis of variance of the number of flowers by tree and crown level is presented in Appendix Table 2. Fewer flower clusters were recorded in the lowest crown level than in the other levels. However, this difference was not statistically significant, although more sampling might make it so. Flowering varied signifi­ cantly between trees, but no consistent relationship was apparent between flowering and larv a l attack by tree s and levels (Appendix

Table 2; Table 19).

Similar analyses of numbers of flowers by quadrants, and in the inner and outer crowns, showed that the differences were non-significant (Appendix Tables 3, 4, and 5).

Mbe£g_of InsectB-_Qn Flowering and Non-flowering Leaf Clusters

A total of 71 leaf clusters out of 3,076 contained egg masses or evidence of egg deposition; 18 of these were on flowering leaf clusters and 53 on non-flowering leaf dusters. Table 13 indicates that there was little difference in the average number of larvae per leaf cluster on flowering and on non-flowering shoots in

1953 and in 1955. 79

T ab le 13

Numbers of P. genlculata Larvae on Flowering and on Non-flowering Leaf Clusters on Four S. auouparia Trees in 1953 and in 1955."

Flowering Non-flowering leaf clusters No. No. le a f Av. no. No. No. le a f Av. no. leaf clusters Total larvae leaf clusters Total larvae clusters with no. per leaf clusters with no. per leaf Year sampled larvae larvae cluster sampled larvae larvae cluster

1953 371 37 217 0.6 977 77 467 0.5

1955 426 34 689 1.6 598 73 1068 1.8

Little or no evidence was obtained of a relationship between eg g and larval distribution and the occurrence of flowers, but more sampling is needed. POPULATION SAMPLING

The sampling of egg and larval populations was not undertaken to develop life tables or to establish a method of

measuring population changes from year to year. A number of factors,

including the time and assistance available, and the scarcity of suf­

ficient suitable trees, precluded any serious consideration of such

objectives. Rather, the primary object of sampling was to obtain

information on the location of eggs and the distribution and feeding habits of larvae within the tree crown. Because information on distribution of the insect within the tree crown and inter- and

intra-tree variability is basic to the development of techniques for

intensive population studies or for extensive surveys, some of the

conclusions drawn from the present study may be useful in population research on this or related species.

This insect is largely a group feeder until the third

instar, after which the individual larvae tend to disperse. Also, general observations suggested that large numbers of larvae in the

early instars are present on apical leaf clusters and that feeding progresses to inner crown foliage as the insect develops. Accordingly, it was felt that two samplings were necessary to provide full infor­ mation on larval distribution and trends of migration within the crown. The f i r s t sampling was ca rrie d out when th e larvae were in the gregarious feeding stages and the second was undertaken when many of the larvae were feeding singly.

80 81

In 1953 a sampling technique similar to that used for the winter moth by Morris and Reeks (1954) was te ste d . The crowns of four trees were divided into four equal vertical levels, A, B, C, D, from the top of the crown to the base. Each crown le v el was partitioned into four quadrants corresponding to the cardinal points of a compass.

Larvae were counted on leaf clusters on a 3-foot branch in each quadrant of each vertical level. The trees were sampled once from

July 14 to July 17. This sampling was inadequate for the following reasons: it failed to test differences between apical and basal leaf clusters; one sampling was not sufficient to indicate possible migratory trends within the crown; the work was conducted too late as most of the larvae were in the fourth and fifth instars and were feeding singly. Only part of the data obtained in 1953 lends itself to analysis.(Table 14).

In 1954 and in 1955 the same basic technique was used except that sampling was conducted twice on each tree and the sampling of each branch included larval counts on four leaf clusters near its apex and four near its base. This provided for the sampling of 16 branches and 128 leaf clusters on each of four trees.

It should be mentioned that the four basal leaf clusters were not necessarily restricted to the same branchlet as the apical leaf clusters, but were chosen from the most basal clusters of the selected branch.

The treeB sampled were ornamental dominant or co-dominant T a b le 14-

Eggs and Larvae of P. geniculata and the Estimated Defoliation on Sixty-four 3-foot Terminal Branches in Four Crown Levels of Four S. aucunaria Trees. Fredericton, N. B. 1953.

Number l e a f E stim ated Number c lu s te r s average Number Crown leaf clusters showing p er cen t egg Number T ree le v e l examined defoliation defoliation co lo n ies la rv a e 1 A 88 0 0 0 2 B 100 15 69 0 99 C 79 12 61 0 148 D 63 8 12 0 120 Sub t o t a l 330 35 — 0 369 2 A 80 0 0 1 0 B 95 3 16 1 0 C 89 8 69 0 11 D 90 28 62 2 1 6 8 Sub t o t a l 354 39 — 4 179 3 A 95 0 0 0 0 B 117 5 6 0 0 C 100 5 52 0 2 D 79 29 79 0 12 Sub t o t a l 391 39 — 0 14 4 A 86 9 30 1 1 B 71 6 27 0 0 C 62 30 37 0 76 D 54 34 74 0 45 Sub t o t a l 273 79 — 1 122 T o ta l 1348 192 — 5 684 83

"S. aucunaria. located some distance from one another on the campus of

the University of New Brunswick in Fredericton. These trees ranged

in height from about 30 to 40 feet and in diameter from about

8 to 12 inches.

Collections were made with pruning shears supported by

interlocking sections of an aluminum extension pole. The cutting

head was fitted with clamping jaws which gripped the cut branch until

it was brought to the ground. Larvae in the early instars were not

easily dislodged but considerable care was necessary with larvae of

the fourth and particularly the fifth instar which dropped readily

when disturbed.

The number of leaves in each leaf cluster was recorded so

the population could ultimately be expressed as larvae per leaf or

larvae per leaf cluster. Morris and Reeks (1954)> in sampling for

larvae of the winter moth, Oueronhtera brumata (Linnaeus), on red

oak, have offered valid reasons why the leaf cluster often offers

greater stability than the leaf in measuring changes in absolute

populations of defoliating insects. They state (p. 438) that WA

reduction in the number of leaves per shoot from one year to the

next would be reflected in an apparent increase in population per

leaf, but not in population per leaf cluster.tt Henson (1954* P* 432)

stated that MIf figures for insect density are required, the

expression of density per unit leaf area is probably the most satis­

factory." It seems likely, however, that high populations of this sawfly would cause d efo liatio n severe enough to prevent a measurement

of leaf area. In the present study the population is expressed as

larvae per leaf cluster.

The gregarious feeding of larvae in the early stages often destroys the egg-bearing leaves and much of the evidence on ovi-

position sites is lost. Thus it is very difficult to make an accurate

appraisal of egg colonies. In some cases the locations of egg

colonies were interpreted from evidence of early larval feeding (see

p. 33). Because such estimates are complicated by more advanced

defoliation found at the time of the second sampling, the data recorded on numbers of egg colonies are considered only for the first sampling.

Egg

In 1954- eggs found on le a f c lu sters in th e outer crown a t the first sampling totalled 17, compared with 5 on leaf clusters in the inner crown (Table 15); corresponding to ta ls in 1955 were 11 and

2 (Table 16).

Eggs found in th e lower orown le v els (C, D) in 1954 and in

1955 to ta lle d 16 and 13, resp ectiv ely , compared with 6 and 0 in the topmost lev els (A, B) fo r these years (Tables 15 and 16).

In 1954 the egg colonies found in the north, east, south, and west quadrants totalled 4> 10, 5, and 1, respectively (Table 17);

corresponding totals in 1955 were 2, 5, 1> and 5 (Table 18). T a b le 15

Eggs and Larvae of £. g»n

Leaf c lu ste rs in outer crown Leaf dusters in inner crown. Av. defol. Av. defol. of le a f Av. defol. Av. no. of le a f Av. defol. Av. no. clu sters of all leaf No. larvae d u s te rs of all leaf No. larvae Crown No. No. affeoted clu sters egg No. per leaf No. No. affected d u s te rs egg No. per le a f

F ir s t Sampling A 64 8 94 12 24- 124 1.9 64 2 41 1 1+ 51 0.8 B 64 3 26 1 1+ 98 1.5 64 4 75 5 24- 2 0.03 C 64 10 46 7 24- 0/|3 3.8 64 3 3 0.1 2 8 0.1 c D _§4 22 42 16 12 837 13.1 J 4 _6 25 2__ 0_ _53 0.8 V Total 256 43 — 9 174- 1301 5.1 256 15 -- 2 54- 114 0.4 Second Sanpling A 64 4 94 6 27 0 — 64 3 46 2 17 1 0.02 B 64 19 51 15 87 78 1.2 64 11 79 14 4+ 13 0.2 C 64 20 70 22 137 43 0.7 64 26 79 32 217 33 0.5 D J 4 2 . 66 42 317 350 _§4 32 62 31 207 132 2.0 T otal 256 82 — 21 547 471 1.8 256 72 • • 20 467 179 0.7

• As larvae in the early instars feed gregariously and usually destroy several leaves, the nusiber of egg easses reoorded in aaapling eust be considered approxlaate. T a b le 1 6

Eggs and Larvae of P. geniculate and Estimated Defoliation of Leaf Clusters in the Cuter and Inner Crown in Four Crown Levels (A, B, C, D, from the top down) on Four European Mountain Ash Trees. Fredericton, N. B. 1955.

Leaf d u s te rs In outer crown ______Leaf clusters in inner crown Av. defol. Av. defol.' I of le a f Av. defol. Av. no. of le a f Av. defol. Av. no. clu sters of all leaf No.* larvae clusters of all leaf No.* larvae Crown No. Ho. affected clu sters egg No. per leaf No. No. affected clu sters egg No. per le a f lev el examined defoliated (ner cent) (per cent) masses larvae c lu ste r examined defoliated (per cent) (per cent) masses larvae clu ster - F ir s t Sampling A 64 13 54 11 2? 287 4.5 64 4 56 4 0 30 0.5 B 64 2 48 2 0 67 1.0 64 0 __ __ 0 1 0.02 C 64 18 57 16 6*1? 423 6.6 64 15 34 8 1 155 2.4 D J* * 76 36 5*2? 322 5.0 64 27 50 21 1+2? 25£ 4.0 Total 256 63 — 16 11+5? 1099 4.3 256 46 — 8 2+27 440 1.7 Second Sampling A 64 3 7 0.3 0 0 - 64 4 ' 6 0.3 0 0 _ B 64 20 76 24 4+1? 23 0.4 64 20 70 22 0 3 0.05 C 64 40 70 44 6+1? 15 0.2 64 40 74 46 1 15 0.2 D J 4 54 68 57 5 96 1.5 64 57 6? 61 7 66 1.0 T otal 256 117 — 31 15+27 134 0.5 256 121 — 32 8 84 0.3

* As larvae in the early instars feed gregariously and generally destroy several leaves, the number of egg masses recorded in sampling must be considered approximate. T a b le 1 7

Eggs and Larvae of £. and Estimated Defoliation of Leaf Clusters In the Outer and Inner Cron In Pour Cron Quadrants (N, E, 3, W) on Four European Mountain Ash Trees. Fredor la ton, N. B. 1954.

^CSaBBSSSIBBBaB& ^aBaCSSaBE=BE^BBSSS:^SSBSB=Sm iBX {^Q tBaB3BBSBSSCai^S1 Iffflf olW.£grg In g&9T grcma------Leaf dusters In In n e r e r o n Av. defol. Av. defol. o f l e a f Av. defol. A v. n o . o f l e a f Av. defol. Av. n o . c l u s t e r s of all leaf N o.* la r v a e d u s t e r s of all leaf N o.* la r v a e Quad­ No. No. a f f e c te d c l u s t e r s eg g No. per leaf No. No. a f f e c te d d u s t e r s egg No. p e r l e a f r a n t exam ined d e f o lia te d ( p e r o e n t) ( p e r c e n t) m asses larvae duster examined d e f o lia te d (p e r c e n t) ( p e r c e n t) m asses I s r v a e c l u s t e r

F irst Sampling

N 64 13 24 5 4+ 455 7 .1 6 4 0 0 2 0 .0 3 E 64 17 79 21 6fr 514 8 .0 6 4 11 36 6 4+ 94 1 .5 S 64 7 50 6 4+ 161 2 .5 64 2 69 2 1 16 0 .2 V _64 67 1+ 171 0 11-15 1 * ± 2 .7 64 1 2■ 1 0 .0 3 2 0 .0 3 T o ta l 256 42 — 9 15+ 1301 5 .1 256 14 ~ 2 5+ 214 0 .4

Second Sampling

N 64 19 66 20 9+ 10 0 .2 64 20 79 25 4+ 6 0 .1 E 64 30 50 23 11+ 447 7 .0 64 25 70 27 9+ 249 2 .3 S 64 18 77 22 10+ 13 0 .2 64 13 64 13 4+ 24 0 .2 V 15 80 19 7+ 1 0 .0 2 64 U 63 14 5+ 10 0 .2 64 — 1 1 ■ ■ ■■ ■■ ■■ T o ta l 256 82 — 21 37* 471 1 .8 256 72 20 2 2 f 179 0 .7

* As larvae in the early instars feed gregariously and usually destroy several leaves, the noaber of egg masses reoarded in sampling must be considered approximate. T a b le 18

Eggs and larvae of £. geniculate and Estimated Defoliation of Leaf Clusters In the Outer and Inner Grom in Four Crown Quadrants (N, E, 3, W) on Four European Mountain Ash Trees. Fredericton, H. B. 1955.

Lwf .slufltaw in gutay srava, Leaf dusters in inner crown Av. defol. Av. defol. of leaf At. defol. A t. no. o f l e a f Av. defol. Av. n o . c lu s te r s of all leaf No. la rv a e d u s t e r s of all leaf Ho.* larvae Quad* Mo. No. affected d u s t e r s •g g No. p e r l e a f No. No. a f f e c te d d u s t e r s egg . Mo. p e r l e a f r a n t exam ined d e f o lia te d (p e r c e n t) (p e r c e n t) la rv a e c lu s te r examined d e f o lia te d (p e r c e n t) (p e r c e n t) masses larvae cluster

F irst Sampling

N 6 4 14 70 15 2 287 4 .5 64 6 42 4 0 8 0 .1 E 64 23 86 31 3+2? 137 2 .1 64 18 51 U 2 361 5 .6 S 64 18 53 15 1+2? 408 6 .4 64 14 29 6 0 57 0 .9 V _64 _8 23 _3 5+1? 267 4 .2 _8 *4 _8 2? _14 0 .2 T o ta l 256 63 — 16 11+5? 1099 4.3 256 46 8 2+2? 440 1 .7 Second Sampling

N 64 25 70 27 2 9 0 .1 64 30 75 35 2 7 0 .1 E 64 28 69 30 3 46 0 .7 64 31 81 39 1 6 0 .1 S 64 38 84 50 8+2? 14 0 .2 64 36 60 34 4 59 0 .9 1 12 0 .2 W 64 26 44 18 _Z__ 65 1.0 M 24 57 a T o ta l 256 117 — 31 15+27 134 0 .5 256 121 — 32 8 84 0 .3

• As larvae in the early instars feed gregariously and usually destroy several leaves, the number of egg masses recorded In sampling must he considered approximate. 89

Lagvg

Leaf dusters sampled in 1953, 1954, and 1955 totalled

1,348, 1,024, and 1,024, respectively (Tables 14, 15, and 16).

Corresponding totals of larvae were 684, 2,065, and 1,757, which

indicates that the average number of larvae per leaf cluster for these years was 0.5, 2.0, and 1.7.

Tests of Differences.—Of 2,048 leaf clusters sampled in

1954 and 1955, a total of 1,368 contained no larvae. Because of this

prevalence of zeros a complete analysis of variance of the data was

not feasible. However, with considerable condensation of the data

it was possible to test the significance of the effects of crown

levels, quadrants, radial distances of leaf clusters on branches,

dates of sampling, and some of their two-factor interactions.

Snedecor (1946) has indicated that the analysis of variance is valid only when th ere is no re la tio n sh ip between th e variance and th e mean.

If the variance shows dependence on the mean the relationship may be removed by transforming the original variates to logarithms. A pre­

liminary analysis of the tables did not indicate a systematic relationship of this type, so the data were not transformed. The late Mr. C. Reimer, Statistical Research and Service Unit, Research

Branch, Department of Agriculture, Ottawa, has indicated (personal

correspondence) that even if some relationship exists between the variance and the mean, the F-test in an analysis of variance will

seldom lead to erroneous conclusions* 9 0

Tabulations used in the analyses of variance were extracted

from sampling data compiled in 1954 and 1955 (Appendix Tables 6, 7,

8, 9 , 10, and 11) and were based on the following substitutions: by

letting X equal the total number of larvae found in a sample of four

leaf clusters, then

XqI = number of larvae in outer crown sample, f i r s t sampling.

Xq2 = number of larvae in outer crown sample, second sampling.

X jl = number of larvae in inner crown sample, f i r s t sampling.

Xj2 - number o f larvae in inner crown sample, second sampling.

The analysis of variance was carried out in four sections

in which the effects of the following factors were tested:

(a) Crown le v e l (L) and crown quadrant (q) by tabulating the sum

Ya = XqI + Xq2 + Xjl + Xj2 (Table 19 and Appendix Table 12).

(b) Radial distance (R), that is, inner versus outer crown, and

the interactions (RL), (RQ) be tabulating the sum

Yb = XqI + Xq2 - Xil - Xj2 (Appendix Tables 13 and 14).

(c) Sampling dates (S), and the Interactions (SL) and (SQ) by

tabulating the sum Yc = XqI - Xq2 + Xjl - Xj2 (Appendix

Tables 15 and 16).

(d) The interactions (RS) by tabulating the sum

Yd = XqI - Xq2 - Xjl + Xj2 (Appendix Tables 17 and 18).

Eight 4 * 4 tables of Y-values, based on data collected in

1954 and 1955 were constructed, and tests for significance of differences carried out. Significance is expressed at the 1 and 5 per cent levels. The sums of squares for error are sums of all higher order interactions and vary with the analyses.

Table 19

Number of £. geniculata Larvae Recorded on §. aucunaria ty Tree and Crown Level in 1954 and 1955.

Level A B CD Total Tree 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955

1 1 313 65 3 12 275 429 254 507 845 2 6 4 26 91 209 261 203 163 444 519 3 0 0 0 0 11 70 346 134 357 204 4 169 0 100 0 94 2 394 187 757 189 Total 176 317 191 94 326 608 1372 738 2065 1757

An example of the calculations of sums of squares, using the above to ta ls for 1954, is as follows;

E i2 = (l)2 + (65)2 + — + (394)2 1 = 596483

Correction factor, C = (2065)2 = 266514 lS Trees SS = (507)2 + — (757)2 _ c 4 = 22157

Levels SS = (176)2 + - - (1372)2 - c 4

= 247515

Trees x Levels SS = 596483 - (other SS)

= 60297 92

T able 20

Analysis of Variance of Humber of £. geniculata Larvae Collected on S. aucuparia by Tree and Crown Level in 1954- and 1955.

■ ■■■ ------■ - -...... ------■ - n T - 4 Source Degrees Sums of Mean of of pqufl.pep F P v ariatio n freedom 1954 1955 1954 1955 1954 1955 1954 1955

Correction facto r 1 266514 192940 — Trees 3 22157 72241 7386 24080 1.10 3.06 >.20 >.05<.10 Levels 3 247515 62968 82505 20989 12.31**2.67 <.01 >.10<.20 Trees x levels 2 60297 70786 6700 7865 Total 16 596483 398935

** Significant within 1 per cent level

Table 20 shows that in 1954 the larval counts varied signifi­ cantly between crown levels (averaged over all quadrants, over all trees, over inner and outer crown samples and over both dates of sampling). Greater numbers were found in the lower parts of the crown

(Table 19). In 1955 the differences were not significant. The inclusion of larg er numbers of tree s undoubtedly would increase the sensitivity of these tests of significance.

Defoliation records also provide information on larval distribution. Tables 15 and 16 indicate that more leaf clusters were defoliated and the average defoliation for all leaf clusters was 93

higher in the lower crown levels (C and D) than near the top of the

crown in 1954 and 1955. The average defoliation of leaf clusters

sampled in 1953 showed a similar pattern by crown levels (Table 14) •

This indicates that larval distribution by crown levels is

not uniform and it is recommended that all levels be represented in

future larval sampling.

Crown Quadrants.—In 1954 more larvae were found in the

north and east quadrants (particularly the east) than in the others

Appendix Table 12). The differences between quadrants were statisti­

cally significant when averaged over all levels, over all trees, over

both inner and outer crown samples, and over both dates of sampling.

Defoliation records agree with these differences (Table 17). In 1955

significant differences between quadrants were not found, but differ­

ences between trees were significant.

It seems evident that the distribution of larvae by crown rquadrants must be studied further before conclusions are justified. A

consistent difference associated with quadrants would not be expected,

however, as larval population studies on two other defoliators, the

w inter moth, and th e spruce budworm, C horistoneura fum lferana

(Clemens), did not show any significant quadrantal variance (Morris

and Reeks, 1954; Morris, 1955).

Outer and Inner Crown by Levels.—In 1954 the difference

between numbers of larvae found on outer crown leaf clusters and those

found on inner crown leaf clusters (averaged over all trees, all

levels, all quadrants, and both sampling periods) was significant 94

(Appendix Table 13); that is, the counta in the outer crown were on the average higher than those in the inner crown (test of mean square for R produced ”Fn value of 37.25)* Moreover, the difference in numbers between the outer and inner crown was not the same at all levels, and decreased from the bottom to the top levels. A corre­ sponding treatment of the 1955 data showed that differences in larval numbers between the outer and inner crown were not statistically significant.

Outer and Inner Crown by Quadrants.--The difference in numbers of larvae between the outer crown and the inner crown was not the same in a ll quadrants in 1954 or in 1955 (Appendix Table 14).

This difference was greater (but not necessarily significantly greater) in the north and east quadrants in 1954, and greater in the south and west quadrants in 1955. In 1955 the difference in numbers between the outer and inner crown varied significantly between trees.

F irst and Second Samplings bv Levels.—Averaged over a ll trees, all levels, all quadrants, and the inner and outer crown the differences in numbers of larvae between the first and second samplings were not statistically significant in 1954 or in 1955

(F = 0.99, 6.9, respectively) (Appendix Table 15). In 1954 the difference in numbers between sampling periods varied significantly between trees; more larvae were found at the first sampling than at the second sampling in trees 2 and 4, whereas in trees 1 and 3 the reverse occurred. Any factors which might account for this differ­ ence in seasonal variation between these trees are not apparent. 95

Fix at and Second Samplings by Quadrants.—A statistically significant inter-tree difference was obtained in numbers of larvae collected between sampling periods in 1955 (Appendix Table 16); trees 1 and 2 produced higher counts at the first sampling than at the second sampling than trees 3 and 4»

Outer and Inner Crown in Different Sampling Periods by

Levels.—Averaged over all trees, all levels, and all quadrants the difference in la rv a l numbers between the outer and inner crown was not significantly different in one sampling period than in the other in 1954 or 1955 (Appendix Table 17). In 1955 ra d ia l differences in numbers between sampling periods varied significantly between trees.

Outer and Inner Crown in Different Sampling Periods fry

Quadrants. —Appendix Table 18 shows that in 1955 the degree of larval migration from the outer to the inner crown between sampling periods was not the same in all trees or in all quadrants.

Even though the average difference between numbers of larvae found in outer crown and inner crown le a f clu sters a t d iffe r­ ent sampling periods was not statistically significant (possibly because of the limited numbers of trees sampled), the following defoliation records from Tables 15 and 16 provide evidence of the tendency for larvae to feed from the outer leaf clusters to the inner leaf clusters} 96

Outer crown leaf clusters rtwrtftEB Number Av. per cent Number Av. per cent defoliated dMoliation, ftefoAlflM 12 & F ir s t sampling 43 9 15 2 Second sampling 82 21 72 20 1955 First sampling 63 16 46 8 Second sampling 117 31 121 32

These figures indicate that more defoliation was apparent on the outer leaf clusters at the first sampling, bub at the second sampling th e re was l i t t l e d ifference in th e number of le a f c lu s te rs defoliated and the loss of foliage between outer and inner leaf c lu s te rs .

To summarize, the larval density differed between levels, between quadrants and between the inner and outer crown in 1954> but not in 1955. In 1955 differences in larval numbers between trees were found. The difference between inner and outer crown densities was associated with levels in 1954; with trees in 1955 f and with quadrants (not the same quadrants) in both years. The average difference in density between first and second samplings was not statistically significant in either year, but significant inter-tree differences between sampling periods were found (but not consistent in particular trees) in both years. The average difference in numbers of larvae between the inner and outer crown was not 9 7

significant between sampling periods in 1954 or 1955,^£ut radial

differences in numbers between sampling periods varied significantly

between trees and between quadrants in 1955.

It is evident that sampling of a larger number of trees is

required before broad conclusions are warranted. Sufficient evidence

has been obtained, however, to recommend that a sampling program for

this insect should include all levels, all quadrants, and outer and

inner crown leaf clusters. The results indicate that two separate

samplings are unnecessary. Sampling should commence when the majority of the larvae are in the third instar; it should terminate before larvae complete the fourth instar, as at this time male larvae drop to the ground and spin cocoons.

Frequency Distribution.—The nature of the frequency distribution is not considered pertinent to this study. However, the rapid development of sampling techniques in the past few years has placed increased emphasis on the distributions of forest insect populations and their role in the development of sequential sampling plans and other statistical designs. An analysis of these data may be useful in suggesting the distribution that may be expected with more adequate d ata.

Waters (1955) states that forest insect survey data will generally be fitted by one of the four following distributional binomial, negative binomial, Poisson, or Normal. These distri­ butions were respectively applied to data by Ives and Prentice (1958),

Morris (1955)> Reeks (1956), and Stark (1952). Morris (1955, p. 26l) has indicated that ..."The most direct way to ascertain the nature of the frequency distribution for a given insect species is to examine a large number of sample units

(preferably several hundred) collected at the same time and place*

The re s u lts can be lis te d in a frequency ta b le and compared d ire c tly , by chi-square tests, to the theoretical frequencies that would be expected when different types of distributions are assumed. When such large-scale sampling at one time and place is not practical, the nature of the distributions can generally be deduced from the relationship between variance and mean....n

Bliss and Fisher (1953) have shown that the negative binomial distribution applies to many different kinds of biological data, including counts of plants and animals* In this distribution the relationship between the variance and the mean is curvilinear, and is approximated by the expression: s^ e X + 5 & /k . The distribution can arise for several reasons, including a heterogeneity in the probability of occurrence of insects between sample units because of eggs being laid in masses, or the insect possessing a gregarious habit.

The data obtained in the present study are too limited to show the exact nature of the frequency distribution but they will show something of the relationship between the variance and the mean* The variance and th e 99 mean (x) of larval numbers were calculated for 54 groups of four le a f clu sters (outer and inner crowns a t two samplings) in 1954 and for 57 such groups in 1955.

The plotted points in Figure 31 indicate that the variance does have a curvilinear relationship to the mean, such that "over- dispersion" probably occurs; "over-dispersion" has been used by Bliss and Fisher (1953) to indicate that the variance is significantly larger than the mean. This suggests that a transformation is desirable to remove the relatio n sh ip between the variance and the mean, and make s2 independent of x. According to Snedecor (1946), this is necessary for tests of significance. However, the foregoing analyses were based on sums and on means, which are known to tend to be normally distributed even when drawn from a non normal d istri­ bution of original variates* Moreover, as previously indicated

(p. 89), the F-test in an analysis of variance is known to be fairly efficient even when there is a relationship between the variance and the mean. The separate curves (s2 = S + S^A) for data in 1954 and

1955 are based on the assumption that the distribution is negative binomial, a distribution that is described by two parameters, the mean (x) and an exponent k. Several mathematical methods of esti­ mating k have been established by Anscombe (1949). In this study, the values of k were approximated by the formula k = ]> x2 /£>s2 “ as used by Morris (1955). The values of k for 1954 and for 1955 were 0.77 and 0.41, the differences between which were not analyzed fo r significance. However, i t is Figure 31. Relationship between variance and mean for larval numbers on leaf clusters in 1954- and 1955. The open and closed circles represent populations in 1954 and 1955. Each point is based on numbers of larvae on four leaf clusters. S2 = variancej x = mean. In set shows points below x = 5 on an expanded scale. 5500

9000

4500

4000

3500

3000

2000

1500

1000

500

20 35 4 0 45 5 0 55 60 F ig u re 31 102 interesting to note that these k values are considerably smaller than that calculated by Morris (1955) for spruce budworm larval and pupal populations (k = 8.217). This indicates greater "over- dispersion" of sawfly data, -which may be due in part to the differ­ ences in sampling methods. On the other hand, the gregarious feeding habits of the sawfly, not demonstrated by the spruce budworm, probably contribute to the greater "over-dispersion.*

Cocoon

The sampling and analysis of cocoons was conducted primarily to obtain information on populations, on the kind and extent of natural control factors in the soil, and to provide some evidence on the depth of soil in which cocoon-spinning occurs.

In 1953 cocoon sampling was carried out by allowing the larvae to fall into earth-filled trays upon the completion of feeding. Each tray, measuring 1 square foot in surface area and

2 inches in depth, with copper screen bottom, was divided into four quadrats by tin strips (Figure 32). This partitioning of the squares was done for replication and to impede wandering of larvae.

Four trays were placed under the canopy of each of four trees.

This provided 16 large sampling units and a total of 64 small units.

Following larval drop the squares were covered with balsam fir brush for overwintering. The following spring observations on adult emergence were made daily during the latter pert of June and early July. Subsequently the soil in each square was sifted to 103

Figure 32. Four 1-square-foot earth- filled sampling trays used for collecting cocoons of P. geniculate. Note that each square is partitioned by two 1* x 2" tin strips into four £-foct quadrats. 104-

obtain cocoon totals and evidence of parasitism and predation. The

same methods were used in 1954- except that the earth in the trays was sifted for cocoons soon after larval drop.

Also in 1954) eleven 1-square-foot samples of soil were

collected near the base of the four permanent sample trees. All the soil and debris were collected and examined from the ^-inch, one-inch, and two-inch levels.

The results of using the 1-square-foot trays under the canopies of trees to sample cocoons were disappointing. Only two adults (l

Evidently the trays were inadequate for cocoon sampling.

Probably some larvae crawled out of the trays, after dropping, to spin cocoons elsewhere. The chief reason why more cocoons were not found in the sampling trays may be predation. Several catbirds,

Dumetella carolinensis Linnaeus, were observed eating sawfly larvae that had dropped into the squares.

The eleven 1-square-foot samples of soil collected near the bases of four sample trees produced a total of 940 sawfly 1 0 5 cocoons, most of which were one or more years old. Of these, 532 were found at the -^-inch level, 339 were collected in soil inch to 1 inch deep, and 69 cocoons were found as deep as 2 inches

(Table 5). This means that about 93 per cent of the cocoons were found in the first inch of soil.

Information on predation and fungus diseases obtained from the analyses of these cocoons is presented in the section on natural control. NATURAL CONTROL FACTORS

Climatic Factors

Temperature and Humidity

The influence of temperature and humidity on the development of P. geniculata has been studied to some extent by others. Brown and Daviault (1942)> in investigating the influence of temperature on the development of various sawflies after hibernation in cocoons, showed that P. geniculata has a rather high thermal constant, requiring 709 and 714 day degrees for males and females, respectively, to complete development. On the other hand they showed that the insect has a low theoretical threshold of development of 34*5° F. for males and 35.1° F. for females. The-high thermal constant would seem an important limiting factor to development in more northern latitudes. However, as indicated by these worker b, the low threshold enables the insect to utilize sufficient heat from the low spring ground temperatures in that area to overcome the handicap of requiring a high total of effective temperature.

Daviault (1947a), with three lots of 150 larvae each reared at three constant temperatures of 52° F., 64*4° F., and 80° F., showed that the percentage of emergence in the same season was 30.6,

42.2, and 8.5, respectively. In further studies Daviault (1947b) observed that the optimum temperatures for all stages of the insect are between 68° F. and 73.4° F.j he concluded that the sawfly will

1 0 6 107

th riv e and cause damage in North America wherever th e mean

temperature during the development of egga and larvae is near this

optimum*

Ife have already seen (p. 21) that the known distribution

of £. geniculata in North America, Europe, and Asia ranges from about

40° to about 56° north latitude* Figure 14 also includes Isotherms

of mean January and July temperatures for areas of known sawfly

occurrence* In Europe the insect has been found in areas which lie

between the January isotherms of 20° F. and 40° F. In North America the sawfly is known to occur within areas where the mean January temperature ranges from about 10° F. to slightly above 30° F, In

Asia the known area of distribution lies between the January

isotherms of 0° F. and 10° F. The range of the July isotherms in relation to distribution of the sawfly Is much less. In Europe and

in North America P. geniculata has been collected from areas where the mean July temperature is slightly under 60° F. to areas where the

July mean is slightly over 70° F. In Asia the areas of known distri­ bution of the sawfly are between the July isotherms of 60° F. and

70° F .

Brown and D aviault (1942) showed th a t dry conditions ten d to retard development* Daviault (1947b) indicated that the adult life is greatly prolonged in dry conditions, particularly at low temperatures, but that longevity.is much reduced in extreme dryness ; at the highest temperatures adults were very active when the atmosphere was humid and longevity was greatly shortened* Further, 108 he showed that prepupal and pupal development could not be completed at humidities lower than 50 per cent, because the dried wall of the cocoon could not be pierced ty adults ready to emerge; on the other hand, mortality was also high in a completely saturated atmosphere.

In discussing humidity requirements for sawflies in general Benson

(1950) indicated that the optimum humidity for many eggs, larvae, prepupae, and adults is almost 100 per cent; he says that cocoons can only be made successfully in this high humidity and it must be maintained for the development and emergence of adults. He concludes that many adults are unable to emerge if the cocoons are dry and hard.

In the present study, dead adults were commonly found in dried cocoons.

Raizenne (1957) reported that 763 adults were reared from

5,796 larvae kept at temperatures as low as 20° F. for several monthB and then incubated at about 75° F. This represents a rearing mortality of about 87 per cent. Mortality of material reared at the Fredericton laboratory was similarly high, using much the same procedures and about 75 per cent relative humidity in incubation; this mortality was not less than 76 per cent in any year.

It is evident that temperature and humidity are important factors in determining the distribution, development, and mortality of this insect. It is equally apparent that considerable infor­ mation is needed for successful rearing, particularly on the optimum 109 humidity for cocoon spinning, the degree and duration of cold exposure, and the amount of moisture necessary for the development and emergence of adults.

Heavy rains and high winds often dislodge larvae from leaves. The rearing of many larvae in the laboratory showed that when larvae fell from the foliage, particularly in the early instars, they were unable to regain their feeding positions and almost always died of starvation.

The effects of wind and rain were tested by placing a

4--square-foot cotton-bottomed tray beneath leaf dusters that sup­ ported a colony of 65 larvae; following a high wind 27 larvae were present on the tray. On another occasion the number of larvae on a branch was reduced from 72 to 4 6 by heavy rains. On August 31 * 1954» a total of 31 larvae issued from eggs under observation in the field on September 1, following the high winds and heavy rains from hurricane "Carol*, none of these larvae was present on the foliage.

Relation between Rainfall and Infestation Intensity.—

Further evidence of the importance of rainfall as a mortality factor was obtained by comparing rainfall averages with sawfly infestation levels in southern New Brunswick from 1937 to 1956.

Southern New Brunswick, as used here, refers roughly to that part of the Province between 45° and 46° 30' north latitude.

Much of this area is included in the "Southern New Brunswick 110

Climatic Region” characterized by Putnam (1940). He stated that the

area has warm summers (July average in Fredericton 67° F.) and cold winters (Januaiy average in Fredericton 13° F .). The frost free

season averages about 113 days. The mean annual precipitation is

38 inches; normal snowfall is 96 inches. The number of rainy days a year varies from 100 to 150. As he said (p. 139), ..."One of the

chief reasons for the heavy precipitation in the Maritimes is their

location at a point near which practically all the cyclonic storms of North America leave the continent,...n

Rainfall records, from the Monthly Record, Meteorological

Observations in Canada, Meteorological Branch, Department of

Transport, were summarized for the following stations: Woodstock,

F redericton, Sussex, Moncton, S aint John, and S t. George (Appendix

Table 19). As adults, eggs, and larvae of the sawfly may be found

in both June and July in this area, the total rainfall was averaged for these months at these stations to represent general

precipitation in southern New Brunswick. Also, annual rainfall and that for June and July, separately, were similarly compiled.

Data on infestation levels were obtained from the Canadian

Insect Pest Review, Annual Reports of the Forest Insect Survey,

Annual Technical Reports of the Forest Biology Laboratory at

Fredericton, Forest Biology Ranger Reports, and from observations by the writer since 1950. The status of infestations was summarized I l l and classified in three degrees on the basis of defoliation estimates: light-trace to 20 per centj moderate- 30 to 60 per cent; and sev ere- over 70 per ce n t.

The relationship between the average amounts of June-July rainfall at the six stations in southern New Brunswick and the

severity of infestations during the 20-year period is shown in

Figure 33. Table 21 shows that the differences in the average amounts of June-July rainfall (Appendix Table 19) were significant when classified fcy years according to the infestation level the

following year.

Table 21

A nalysis of V ariance of th e Average Amounts o f June-July Rainfall in southern New Brunswick from 1936 to 1955 Classified by Infestation Levels of P. geniculata.

Source o f Degrees Sums of Mean v a ria tio n o f freedom squares square F

Infestation le v e l 2 5.5773 2.7886 4 . 68 * E rro r 17 10.1264 0.5956 T o tal 19 15.7037

■m- Significant within 5 per cent level

Similar analyses showed that the differences in the mean annual rainfall, classified according to infestation intensity the 112 following year, were non significant. Also, differences were non significant when the separate rainfall averages for June and for

July were similarly classified.

Figure 33 shows th a t th e highest r a in f a ll (over 4 inches average) in the 2-raonth period occurred in 1938, 1943, 1947, and

1954- Except for 1947 these years of high rainfall were followed by years of light defoliation; in 1948 defoliation was moderate.

Lesser amounts of rainfall, but above the 20-year mean (3.17 inches), occurred in 1945, 1948, 1950, 1951, and 1953; these years were followed by infestations of moderate intensity in 1946, 1949, 1951, and 1954, and of light intensity in 1952. The years when rainfall was below average in 1936, 1937, 1939, 1940, 19a, 1942, 1944, 1946,

1949, 1952, and 1955 preceded years of either moderate or severe defoliation, except in 1944 when rainfall was only slightly below average and was followed by light infestations in 1945.

The evidence suggests that rainfall In June and July is a significant factor in the determination of sawfly populations the following year. Definite conclusions cannot be drawn, however, until more intensive studies show the mechanisms by which this is brought about, the influence of other mortality factors, and the cause and effect relationship of rainfall on these factors. Morris

(1959) has demonstrated the value of a single factor approach in showing how population changes from generation to generation may be related to a variable ‘key factor,' and how the measurement of Figure 33. The relation between June-July rainfall and infestation intensity of £• geniculata in southern New Brunswick over a 20-year period. Rainfall totals are averaged from six stations. Infestations are shown with a lag of one year.

1 1 3 o o RAINFALL

w Ul u o IN IN INCHES r* in g AVERAGE AVERAGE JUNE- JULY ct Y 09 m < INFESTATION INTENSITY

1937 1938 1939 1940 1941 1942 1943 1944 1945 1948 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 _ . YEAR „ F ig u re .33 1 15 m ortality caused by this factor may have predictive value. Thus it is possible that more study w ill show that rainfall operates as a

’key factor1 in the determination of sawfly density, perhaps through its effect on the action of other factors of natural control.

As adults, eggs, and larvae of P. geniculata may be found during June and July, it is interesting to examine some of the possible effects of rainfall on each of these stages, Uvarov (1931) has cited the observations of several workers regarding the effect of heavy rainfall on the activity and mortality of adult insects. If rainfall during this period resulted in the death of many adults or otherwise reduced mating and oviposition, we would expect that

Infestation intensity would be generally reduced the same year.

However, Figure 33 shows little evidence that rainfall has this effect. Further, an analysis of variance showed that the differences between the average June-July rainfall, classified with infestation intensity the same year, were non significant* As the eggs are embedded in the leaf tissue there seems little reason to suppose that they are seriously affected by heavy rains. Larvae, however, as previously mentioned, are often dislodged from foliage by heavy rains. Similar loss of larvae has been reported in other insects,

Tripp (1956) indicated that heavy prolonged rainfall has an important bearing on survival of larvae of Heodiprion swalnei

Middleton, and he observed that increased numbers of larvae fe ll from foliage when raindrops were large. Beirne (1955, p. 43) stated 1 1 6 that . .."The scarcity of Lepidoptera as a whole in Ireland as compared with southern England, which has been remarked by those experienced in collecting in both regions, may be partly because of the relatively much higher rainfall in Ireland....11

Although the drowning of adults and larvae and the pelting effect of heavy rainfall probably causes considerable mortality, the influence of abundant precipitation in reducing infestations the following year may be more complex than th is. Greenback (1956) showed that the spruce budworm develops more rapidly under clear and dry conditions than under wet and overcast conditions. He indicated that the longer developmental period under adverse weather conditions subjects the insects to increased exposure to attacks by natural enemies, especially birds and diseases. L ittle information was obtained on the effects of adverse weather on the developmental period of the sawfly, but there seems no doubt that wet cool con­ ditions would prolong development. Also, it Is well known that wet conditions favour the incidence and development of fungus diseases.

As P. geniculata larvae spin cocoons in the ground, the influence of wet soil and high humidity in fostering diseases of larvae in cocoons may be important in reducing sawfly populations. Further, it is possible that the influence of heavy rainfall in delaying development may have an important effect on fecundity. In this, connection, M iller (1957) showed that spruce budworm specimens with an early seasonal development have a significantly greater fecundity and pupal weight than those with a late seasonal development. 117

To summarize, the evidence suggests a relationship between

rainfall and infestation intensity of the sawfly the following year*

The complex of factors involved is not well understood and more study

is needed to determine their significance.

Biotic Factors

P a ra s ite s

The literature contains few records of parasitism in this species. Because of this and because of the European origin of the sawfly, an investigation of the numbers and importance of parasites was considered important in establishing a basis for any program of biological control which might be considered in the future. From

1950 to 1957 several thousand Bawfly eggs and larvae were collected for detailed observations and rearing, the results of which are outlined in the following paragraphs.

Egg P a ra s ite s . —The f i r s t reco rd s known to th e w rite r o f egg parasitism in this sawfly were obtained in 1954 when specimens of

Triohogramma sp., apparently mlnutum Riley, were reared from field-collected sawfly eggs at Fredericton. All collections of parasitized sawfly eggs were taken from June 30 to July 12 except one on September 4. Adults emerged from the summer collections from

July 12 to July 15; emergence from the autumn collection occurred on

September 12. This parasite is known to attack 110 other insect hosts representing several orders (Peck, 195l). Sawfly eggs parasitized by this polyembryonic species appear blackish 118

(Figures 34 and 35) J this is caused by the black parasite cocoon formed within the chorion of the host egg (Figure 36). Some immature stages of the parasite are shown in Figures 36 and 37, where it is seen that at least six individuals may develop within one parasite cocoon.

The September record of egg parasitism indicates that the parasite is capable of attacking sawfly eggs of the second generation.

Moreover, parasitism was higher in this collection than in any of the early summer collections, in that almost 61 per cent of the eggs collected were parasitized.

Of 2,128 sawfly eggs examined for parasite and predator attack, 133 were parasitized, indicating that egg parasitism averaged about 6.2 per cent (Table 6).

Larval Parasites.—Apart from two tachinids, Bessa select*

(Meigen) (= Bessa harvevi (Townsend)) and barbatula

Rondani, recorded by Baer (1920), no references to parasitism of P. geniculata in Europe have been found. Only a few parasites of the sawfly have been recorded in North America. Raizenne (1957) listed three tachinids reared in very small numbers from collections taken by the Forest Insect Survey in Ontario from 1938 to 1952, inclusive:

Bessa harveyi (Tns.), Compsilura concinnata (Meigen), and

Neonhorocera hamata Aldrich and Webber. Dr. W. E. Waters^ (private communication) indicated that the tachinids Achaetoneura

1 »■ Leader, Forest Insect Laboratory, Northeastern Forest Experiment Station, New Haven, Connecticut. Eggs of P. geniculata parasitized by Trichogramma sp. apparently minutum Riley

Figure 34-. Blackish eggs on right of leaflet are parasitized. Eggs on left side of leaflet are unparasitized.

Figure 35. Parasite cocoons within sawfly egg pockets. Note parasite emergence hole in the uppermost cocoon.

Figure 36. Epidermal layer of leaflet removed to show parasite cocoons in sawfly egg pockets. The lowermost cocoon has been dissected to show immature stages of the polyembryonic parasite.

Figure 37. Parasite pupae.

1 1 9 120

Figure 34-

F ig u re 36 F ig u re 37 121 tenthredinarufl (Townsend) and Pvtchomla se le c ts Meigen (= Bessa harvevi (TnB.)) are recorded at the Forest Insect and Disease

Laboratory, Northeastern Forest Experiment Station, New Haven,

Connecticut, from sawfly collections taken from a number of locali­ ties in the Northeastern States. Hawboldt (194-7) also reared B. harvevi from the mountain ash sawfly. Unpublished records of the

Forest Insect Survey in Fredericton indicate that small numbers of

B. harvevi and the pteromalid Tritneptis dinrionis Gahan have been reared from the sawfly in the Maritime Provinces.

In the present study several thousand sawfly larvae were reared, primarily for observations on parasitism and disease and many of the cocoons were dissected. No parasites emerged, and except for one unidentified parasite egg present on one fifth-stage sawfly larva (Figure 39), no immature stages of parasites were found. The analysis of 94-0 cocoons taken from one-3quare-foot quadrats near the bases of sample trees showed that only two had emergence holes that could be attributed to parasites (Table 5)j these were very tiny, and may have been made by T. dinrionis. This evidence suggests that parasitism in this region is of very minor importance in the natural control of this sawfly.

Limited attempts to introduoe a European parasite were carried out in the liberation of 1000 specimens of Sturmia sp. in

1948 and 500 in 194-9 at Wellington, Ontario (Biological Control

In v estig atio n s U nit, 194-8, 194-9). This seems to be the only attem pt to date to use biological control methods against this insect. 1 2 2

Figure 38. Eggs of co ccin ellid , Adalia binunctata Linnaeus, believed to be predaceous on eggs and larvae of P. geniculata.

Figure 39. Unidentified parasite egg on fifth-instar larva of P. geniculata. Predators

Insects.--Two species of insects were observed feeding on

eggs of P. geniculata: a tenthredinid sawfly, Macro diva sp., and a

clerid beetle, Fbyllobaenus verticalis Say. The Macronhva was seen to eat five eggs in less than five minutes. The adult clerid female ate sawfly eggs while copulating. Examination of 2,128 sawfly eggs

collected in the field showed that 121 or 5.7 per cent had symptoms of predator attack (Table 6j Figures 40 and 4l)»

Species observed feeding on P. geniculata larvae included the pentatomids Podisus maculiventris (Say) (Figure 42), Podisus serieventris Uhler., and Podisus modestus Dallus. Also, a chrysopid larva, Chrvsopa sp. prob. oculata Say, was seen to destroy several larvae.

Eggs (Figure 38), larvae, and adults of the coccinellid beetle, Adalia bipunctata Linnaeus, were frequently found on the foliage of mountain ash. This species was not observed feeding on the sawfly, but dead sawfly larvae with integumental punctures were found.in cages, where it was present, and there seems little doubt that larvae and adults of A. biuunctata are predaceous on sawfly larvae.

Spiders were commonly observed on foliage in proximity to colonies of sawfly larvae. It is probable that they destroy larvae but such predation was not actually observed.

Of 940 cocoons taken from litte r and soil samples, 86 were 124

Figure 40* Part of S. aucuparia leaflet showing normal egg pockets containing fully- developed eggs of P. geniculata. and an egg pocket (on right) in which the egg has been destroyed by predators.

Figure 41* Excised eggs of P. geniculata showing normal larval embryo on right and one that appears to have been sucked by predaceous i n s e c t s . Figure 42. A hemipterous predator* Podisus maculiventris (Say), attacking a £• ggnipyMfl larva* 126

classed as having been attacked by insects (Table 5). Most such

cocoons had an opening near the middle similar in size and shape to

those made by larval Elateridae in the European spruce sawfly, D.

hercvniae (Morris, 1951b), but a few had large ragged holes, possibly

made by carabids.

Birds.--On several occasions, catbirds, Dumetella

-carolinensis Linnaeus, were observed eating sawfly larvae, particu­

larly in the later stages when larvae were migrating along branches

o r a f te r they had dropped to th e ground. Mr. W. A. Squires-*-

(private communication), however, indicated that the catbird is not

common in New Brunswick, and suggested that there are not enough of

these birds to materially affect sawfly numbers. Further, he stated

that this is in great contrast to the situation in southern New

England and through New York into mid-western states where the

catbird is very common.

Similar predation by an unidentified bird was also observed.

Mammals.—The dropping of full-grown larvae to the ground

where they spin cocoons in the litter and in the upper layers of the

soil not only renders them susceptible to attack by birds on the

ground and by predaceous insects in the soil, but also by small

mammals. Studies of predation by small mammals on the European

spruce sawfly, D. hercvniae. by Balch (1939)> Morris (194^4

■^Curator, Natural Science Department, New Brunswick Museum, Saint John, N. B. 127

Conklin (1942), and on the larch sawfly, Pristiphora erlchsonii

(Hartig), by Graham (1928), Lejeune (1951), and Buckner (1958)

indicated that they are important agents in the natural control of

these pests. Observations on the role of small mammals as con­

trolling factors of £. geniculata were limited to the analyses of

cocoons from the soil sampled in 11 one-square-focrfc quadrats near the

bases o f four permanent sample tre e s . Cocoons opened by mammals were distinguished by criteria illustrated by Morris (1949b) and

Buckner (1958), but no attempt was made to distinguish between those

chewed by rodents and those chewed by insectivores.

Forty-one male cocoons and 54 female cocoons, or 95 out of

94Q examined, showed evidence of small mammal attack (Table 5). This

is probably a conservative count as some of the cocoons classed as

doubtful were old and deteriorated and it could not be established

with certainty that these had been opened by mammals. It has been

pointed out by Morris (1949b) and by Holling (1955) that any

assessment of the control value of small mammals made on the basis of

cocoon collections may be inaccurate because of the overlapping or

mutual interference of various control factors, and because of the varying degrees of selectivity demonstrated by small mammals in

distinguishing between cocoons that are sound or dead from

parasitism or disease.

Disease

Viruses.—Virus diseases are important agents in the 128 control of other introduced sawflies, as shown by Balch and Bird

(1944) and Bird (1954) in the European spruce sawfly, D. hercyniap» and by Bird (1953) in the European pine sawfly, Neodinrion sertifer

(Geoffroy). In the present study all specimens of P. geniculata th a t appeared to show ex tern al symptoms o f d isease were subm itted to the Insect Pathology Research Institute, Sault Ste. Marie, Ontario, for examination* Specimens submitted from Spruce Brook, Newfoundland, in 1951 showed evidence suggesting infection by a capsule virusj also specimens collected in New Brunswick in 1955 at Belle lake and

Nictau Lake road, and in 1957 at Jacquet River contained polyhedra- like bodies. Because of the infrequent occurrence of the granular and polyhedral inclusions in the smears, however, the records cannot be considered positive. Infection tests by Mr. D. E. Elgee*^ and the writer with a small part of the material of the last-mentioned collection thought to contain a polyhedrosis proved negative.

According to Dr. J. MacB. Cam eron^ (private communication) no positive cases of virus diseases have been reported in the genus

Pristinhora.

Fungi.—About 70 cocoons taken from the soil were sent to the Insect Pathology Research Institute for examination; most of these were old and showed little of significance. Three fungi

1 Assistant Technician, Forest Biology Laboratory, Fredericton, N. B. ^Director, Insect Pathology Research Institute, Sault Ste. Marie, Ontario. 129 considered to be secondary were isolatedi Fusarium oxygporum Schl. emend. Synder & Hansen (Figure 43) > Fusarium sp. (Figure 44 )» and

Penicillium sp. Yeasts were isolated from a number of larvae, but these were not pathogenic.

Wolff (1924) observed a fungus on P. geniculata larvae of the second generation in Europe that he considered to be entomogenous. Gordon (1959) recorded the fungus, Fusarium oxvsporum. on material collected by the writer and submitted to him by the

Insect Pathology Research Institute. No other reference to the occurrence of a fungus on P. geniculata has been found.

Bacteria.—Many P. geniculata larvae that died in rearing from unknown physiological causes contained bacteria. The body fluids of several larvae were cultured and sent to the Insect

Pathology Research Institute for diagnosis. All cultures contained saprophytic bacteria, many of which included gram negative bacilli and cocci.

Protozoa. —Mountain ash sawfly larvae collected in New

Brunswick at Berryville, Northumberland County, on August 1, 1957, at

Fredericton on July 9, 1958, and at Patrieville, Madawaska County, on July 29, 1958, were diagnosed by pathologists at Sault Ste. Marie as being infected with microsporidia. These are apparently the first records of sporozoan parasites in P. geniculata. Figure 43. Section of P. geniculata cocoon removed to show mycelium of the fungus, Fusarium oxysporum Schl. emend. Snyder & Hansen, protruding from the thoracic region of a dead larva.

Figure 44. Dried remains of cocooned P. geniculata larva partially covered with a whitish fungus, Fusarium sp. 131

Other Factory

F ailu re of Eggs to Hatch. —I t has been shown th a t parasites and predators destroyed about 12 per cent of sawfly eggs collected at random from the field (Table 6). Other observations on eggs produced by caged ad u lts (cages were removed sh o rtly a fte r eggs were laid) showed that the average percentage of eggs that failed to hatch was about 40 and that egg mortality ranged from 7 to 79 per cent (Table 2). This mortality or failure of eggs to hatch may have been caused by climatic or biotic control factors as well as inviability.

Seven groups of eggs on foliage were placed in individual jelly-jar units containing water in the insectary. The numbers of hatched and unhatched eggs are listed in Table 22.

Table 22

Insectary Observations on Egg Hatching of P. geniculata

No. eggs Number Number Per cent collected hatched unhatched unhatched

IS 48 0 0 112 103 9 8.0 105 102 3 2.8 53 IS 10 18.9 4-8 32 16 33.3 87 62 25 28.7 36.0 2 1 JS 27 I s 528 4-38 90 17.0 132

Starvation. —There is little doubt that food shortages occur* This may be of considerable consequence in natural control through direct mortality and an effect on the reproductive capacity of the survivors, as was shown by Prebble (1941) in the European spruce sawfly and by Heron (1955) in the larch sawfly. However, no instance of obvious food shortage was observed in the field, and apparently there is close synchronization of egg deposition in relation to the available foliage. For example, no more than one group of eggs was ever observed on small trees of breast heightj the larvae from these often completely defoliated the trees (Figures 29 and 30), but seemingly not before larval development was completed.

Abundance and Distribution of Host Tree.—It is well known that monocultures encourage outbreaks of insects. Sorbus does not grow in monocultures in the Maritime Provinces and its spotty and discontinuous occurrence may be an important factor of natural control. The mountain ash sawfly is in a position similar to that of the European spruce sawfly before introduction of parasites and disease; that is, both sawflies were introduced about the same time, both with few effective parasites on this continent, both with diapause, and both with one and a partial second generation per year.

Yet a disastrous outbreak of the latter sawfly occurred in eastern

Canada because of an abundance of spruce in the forests. The mountain ash sawfly, on the other hand, is incapable of reaching high populations per acre because its host is scattered and relatively 133 scarce. On this account, Dr. R. F. Morris^ (private communication) feels that it must be much more subject to density-dependent control factors such as birds and mammals* In the case of the European

spruce sawfly where populations of the insect per acre were high, birds and mammals were unable to exert an important regulating effect of this kind.

Miscellaneous. —Ivbrtalitv of larvae in the field was high.

Counts made daily on colonies of larvae from eclosion to the fourth instar, when they tend to wander and feed singly, showed that many larvae disappeared in the course of feeding and must be presumed dead. Some o f th e known causes o f t h i s m o rta lity have alre ad y been d isc u sse d .

Table 23 indicates that larval mortality in the first instar ranged from 0 to 100 per cent, and averaged 4-5 per cent. The average mortality for second-and third-instar larvae was 19 per cent and 26 per cent, respectively.

Although mortality factors are not completely understood, the evidence available gives an indication of the relative proportions of each stage that appear to succumb to natural control factors. Assuming that the average number of eggs laid per female is 80, we have seen that egg mortality under field conditions

■^Principal Research Officer, Forest Biology Laboratory, F re d e ric to n , N. B. T ab le 23

Field and Laboratory Observations on Mortality of P. geniculata larvae in Instars 1, 2, 3. Fredericton, N. B. 1951-1954*

I n s ta r 1 ______I n s ta r 2 ______I n s ta r 3 O rig in al No. O riginal No. O rig in al No. Obser­ number la rv a e Per cen t number la rv a e Per cen t number la rv a e Per cent v a tio n la rv a e d ied m o rta lity la rv a e died m o rta lity la rv a e died m o rta lity

51-F56 181 46 25.4 135 26 19.2 109 11 10.1 51-57 11 10 90.0 1 1 100.0 — — 51-5*3 37 36 97.3 1 1 100.0 — 52-F1 60 57 95.0 3 2 66.7 1 * * 52-F2 30 29 96.7 1 0 0 1 * •* 52-F3 42 38 90.5 4 2 50.0 2 ** 52-F4 35 29 82.8 6 0 0 6 * 53-F1 46 46 100.0 — — — —— 53-F2 4 3 75.0 1 # -a- st- St- * 53-F3 39 12 30.8 27 4 14.8 23 5 21.7 53-F4 188 33 1 7.6 155 58 3 7.4 97 51 52.6 53-F5 95 84 8 8.4 11 10 90.9 1 1 100.0 53-L1+ 103 84 8 1.6 19 # * •* ** 53-L2* 43 6 14.0 37 * *# * 53-U** 32 0 0 32 0 0 32 0 0 54-F1 201 4 2.0 197 18 9 .1 179 54 3 0.2 54-F2 20 15 75.0 5 0 0 5 ** 54-F3 21 1 4 .8 20 0 0 20 __ 3 15.0 T o tals 1188 122 1 8 .6 476 125 26.3 and av s. 533 44.9 655 + Observations on laboratory-reared material. * Observations discontinued. 135 averaged 40 per centj this leaves 4B eggs that hatched. Using the data obtained on average mortality for the first three larval instars, we see that 22 larvae died in the first instar, leaving 26 larvae to moult to the second stage; 5 larvae succumbed in the second instar, providing 21 third-instar larvae; the mortality in this stage was

5 leaving 16 in the fourth instar. No percentage mortality figures are available for the fourth and fifth stages, but if we use the average percentage mortality for the first three instars, a percentage of 30 is obtained. Applying this to the fourth stage, we see that 5 more larvae died, leaving 11. Now assuming that the sex ratio is about 80 per cent females, we see that 2 male larvae drop to the ground and spin cocoons; a remainder of 9 female larvae which feed throughout the fifth instar is left. Three of these die leaving 6 to spin cocoons. We now have 8 cocoons (2 SS and 6 ^) from our original complement of 80 eggs.

If we accept the mortality estimates obtained for male and female cocoons (Table 5) we see that 67 per cent of the males

(including those classed as doubtful) were destroyed by natural control factors; the corresponding estimate of mortality for female cocoons was 66 per cent. When these estimates of mortality are deducted from the 2 male cocoons and the 6 female cocoons in our hypothetical group, we have a remainder of 0.7 males and 2 females to emerge as adults. 136

These rough estimates suggest an increasing population in the Fredericton area during the period of study, but it should be remembered that the average percentages of mortality adopted for the fourth and fifth instars may not be realistic.

The evidence indicates that P. geniculata is well adapted to conditions in the Maritime Provinces. This insect fluctuates considerably in numbers in response to climatic and biotic control factors, but it lacks adequate density-dependent control factors such as parasites, predators, and diseases. The ultimate limiting factor is the scattered distribution of its food supply. This suggests that it is a pest because it lacks an effective complex of natural enemies to prevent it reaching levels at which severe defoliation takes place. It appears to be a case where the introduction of parasites, predators, or disease might have beneficial results. SUMMARY AND CONCLUSIONS

The biology of the mountain ash sawfly, Pristlphora geniculata (Hartig), an introduced insect, was studied at Fredericton,

New Brunswick, between 1950 and 1957.

This insect was described by Hartig in 1840 as Nenatus geniculatus. In 1883 it was re-described as Nematus cheilon Zaddach.

In 1890 Konow placed the species in the genus Pristinhora and retained Hartig's geniculata.

This sawfly has been reported on Sorbus aucanaria Linnaeus in Europe* The most common hosts in North America are S. aucunaria and S. americana Marshall. In the Maritimes it was also found on

S. decora (Sargent) Schneider, Sorbaronia hybrids (Moench) Schneider, and Prunus virginiana Linnaeus. The distribution and characteristics of the principal hosts are described.

P. geniculata has been found in England and Ireland, and throughout much of continental Europe, in eastern North America, and on the Kamchatka Peninsula in Asia. It has been located as far south as Lawrenceville, New Jersey (about 40° north latitude) and as far north as Silini, Latvia (about 56° north latitude). It has been collected in areas roughly between the January isotherms of 0° F. and

40° F., and in areas approximately between the July isotherms of

60° F. and 70° F.

Standard techniques were used in field and laboratory

137 138 observations on habits, development, and natural control factors of all stages of the insecrt, and on radial and shoot growth studies of the host tree. Information on the occurrence of eggs, the distri­

bution and feeding habits of the larvae within the tree crown, and

flowering and growth characteristics of the host tree, was obtained by the following sampling technique: the crowns of four European mountain ash trees were divided into four quadrants corresponding to the cardinal points of a compass. The sampling of one branch from

each quadrant of each crown level included larval counts on a ll

leaf clusters on a 3-foot branch in 1953. This was modified in 1954

and 1955 to include larval counts on four leaf clusters near the

apex of the branch and on four near its base. One sampling was

conducted in 1953 and two in 1954 and 1955, the first when the larvae were feeding gregariously, and the second when most larvae were feeding singly. Cocoon sampling was carried out by using earth-filled trays with screen bottoms placed under the canopies of sample trees.

£. geniculata overwinters as a larva in a cocoon in the litte r or just below the soil surface. Some larvae remain in

diapause. Others pupate in the spring, and adults emerge during the latter part of June and early July. Oviposition occurs soon after emergence. Larvae feed from two to three weeks and then drop to the

ground and spin cocoons. Some individuals produce a second gener­

ation in August and September but most have only one generation. 139

The pearl gray, elliptical eggs are laid around the periphery of the leaflet between the epidermal layers. These hatch in from 6 to 13 days depending on temperature. The number of eggs laid by single females ranged from 17 to 150, averaging 80.

Larvae of the first three instars are pale green to yellow with heads and thoracic legs dark brown to black. Larvae with yellow heads and yellow thoracic legs in the fourth instar are males in their ultimate instar. Larvae with dark brown to black heads and thoracic legs in the fourth instar are females. These have yellow heads and yellow thoracic legs in the fifth instar. Black spots occur on the thorax and abdomen of larvae in instars 2 to 5. Larvae of the first two instars feed gregariously, while those of the later instars often feed singly. Cocoons from which males emerged averaged 6.4 mm. long and 2.9 mm. wide; corresponding averages for

"female" cocoons were 8.6 mm. and 3.9 mm. The duration of the pupal stage varied from 8 to 12 days.

The adults are near black with mouthparts and legs mostly pale. A comparison of the colour pattern, median fovea, wings, ovipositor sheath, lance, and lancets of Canadian female adults and one European female did not show any important differences.

Measurement of the daily frass drop showed that the range of feeding was close to the 20-day larval feeding period recorded for females in the field and in the insectary. Frass drop increased with high mean temperatures. The average weight of frass ejected by individually reared female larvae in the inBectary was almost 1 4 0

three times that ejected by males. About 75 per cent of frass by weight was ejected by both males and females in the ultimate instar,

in dicating th a t most of th e food i s consumed in th is in s ta r.

A sex ratio of 21 per cent males and 79 par cent females was obtained by rearing adults. Females may lay eggs parthenoge-

netically. These develop to males, indicating that parthenogenesis

is facultative and arrhenotokous. The proportion of sexes from year to year probably varies, but these fluctuations may be affected

by the tendency of females to oviposit soon after emergence and the

possibility of a sex difference of specimens entering and remaining

in diapause.

Five discrete groups were obtained by plotting the head widths of 451 larvae. This supported other evidence that there are

five feeding instars, and means that the instar may be reliably determined by head-width measurement, in the absence of serious nutritional or environmental effacts. Head widths of 54- female larvae in th e fourth in s ta r averaged 1.44- mm., compared with 1.37 mm. for 56 male fourth-instar larvae. This difference was statistically significant. The weighted sums of squares of the differences between the observed means and those calculated by seven methods were as follow: Dyar’s ratio, 1.641; an average growth ratio,

2.04-7; a logarithm ic growth r a tio , 2.242; lin e a r regression equation y = a + hoc, 1.260; regression equation log y = a + bx,

1.409; parabolic equation y = a + hx + cx£, 0.193; and equation i a

log y = a + bx + cx?, 4.278. It is concluded that, of the methods

tested, the parabola y = a + bx + ex? gives the best description of

the increase in size of head capsules.

Measurement of the growth of two S. auouoaria trees

showed radial and shoot growth commenced about May 1. Shoot growth

terminated about July 7 when radial growth was about 50 per cent

complete. Radial growth continued until September 23. Most larval

feeding at Fredericton occurs between July 6 and August 6 when the

majority of larvae are in the fourth and fifth instars. At this

time trees have completed 50 to 75 per cent of their radial growth

and almost all their shoot growth. It is postulated that the trees

can withstand considerable defoliation year after year with

apparently little effect because most of the foliage is destroyed

at this time rather than early in the season, and because most

defoliation oocurs in the lower crown levels. Refoliation occurred

on most shoots that had lost 80 per cent or more of their leaves.

Where loss of the first crop of foliage was less than 80 per cent,

refoliation was rare. Fewer leaves were produced in the second crop than in the first crop of foliage.

The differences in numbers of flowers on four g. aucunaria, trees by crown levels, crown quadrants, and outer and inner crowns were not statistically significant. There was little or no evidence of a relationship between egg and larval distribution and the occurrence of flowers. Outer crown leaf clusters contained about 142 four times as many eggs as inner crown leaf clusters. About five times as many eggs were found in the lower half of the crown as in the upper half. The most eggs were found in the east and south quadrants in 1954 and in the east and west quadrants in 1955*

The sampling of 3,402 leaf clusters produced 4,506 larvae.

The average number of larvae per leaf cluster for 1953, 1954, and

1955 was 0.5, 2.0, and 1.7. More larvae were found in the lower crown levels than in the upper levels. These differences were statistically significant in 1954 but not in 1955. Differences in larval numbers between quadrants in 1954 and between trees in 1955 were statistically significant. Significantly greater numbers of larvae were found on the average in the outer crown than in the inner crown in 1954, but not in 1955. In 1954 the difference in numbers between the outer and inner crown was not the same at all levels and decreased from the bottom to the top. The difference in larval numbers between the outer and inner crown varied significantly by quadrants in both years and by trees in 1955. The average difference in density between first and second samplings was not statistically significant in either year, but significant inter-tree differences between sampling periods were found in both years. The average difference in numbers of larvae between the outer and inner crown was not significant between sampling periods in either year, but radial differences in numbers between sampling periods varied significantly between trees and between quadrants in 1955.

Sampling should be carried out on a larger number of trees, 143 and should include all levels, all quadrants and leaf clusters in the outer and inner crown. One sampling is sufficient but it should be started when most of the larvae are in the third instar, and terminated before the completion of the fourth instar.

The relationship between the variance and the mean of larval numbers found on leaf clusters in 1954- and 1955 was curved, indicating that nover-dispersionn (variance significantly larger than the mean) probably occurs. This n over-dispersion” is probably due mostly to the gregarious feeding habits of the sawfly.

Cocoon sampling by using earth-filled trays under the canopies of sample trees was unsuccessful, probably because catbirds destroyed most of the larvae. The analysis of soil samples in

1-square-foot quadrats showed that 57 per cent of the cocoons were at the -£-inch level, 36 per cent were between inch and 1 inch, and

7 per cent were as deep as 2 inches.

The sawfly is difficult to rear in the laboratory—mortality being no less than 76 per cent in any year. Information is needed on moisture requirements and the degree and duration of cold exposure necessary for successful development and emergence of adults.

Rainfall and winds cause important mortality in the field.

A relationship was shown between the average amounts of June-July rainfall and the severity of sawfly infestations in southern New

Brunswick over a 20-year period. High rainfall one year was usually followed by light infestations the next year. Tears when rainfall 144 was below average usually preceded years of moderate or severe defoliation# The mechanisms by which this is brought about are postulated, but more study is needed to determine the significance of the factors involved*

Egg parasitism averaged about 6 per cent. The only egg parasite reared was Trichogrftmmft sp. apparently minutum Riley, apparently a new record on this host* Small numbers of the tachinid,

Bftssa harvard (Townsend), and the pberomalid, Tritnentia dinrionia

Gahan, have been reared from P. geniculata by the Forest Insect

Survey at Fredericton since 1936. Larval parasitism in the present study was negligible.

About 6 per cent of sawfly eggs were destroyed by insect predators. A tenthredinid sawfly, Macrouhva sp., and a clerid beetle, Phvllobaenus verbicalis Say, were seen to feed on eggs.

Predators of larvae included the pentatomids, Podisua maculiventris

(Say), P. serieventris Uhler., P. modestus Dalius, and a chrysopid larva, Chrvsona sp. prob. oculata Say. Spiders also probably destroy larvae. Catbirds were often observed destroying larvae.

About 9 per cent of cocoons collected in the field showed evidence of attack by insects, probably by elaterids and carabids. About

10 per cent of field-collected cocoons appeared to have been a tta c k e d by sm all mammals*

No positive cases of virus infection and no evidence of attack by primary fungi were found. Saprophytic bacteria were 145 common in larvae that died in rearing. Microsporidian parasites were found in larvae from three areas of New Brunswick, apparently for the first time on this insect.

Other factors of natural control that may be important are: (l) egg mortality or failure to hatch, which ranged in the field from 7 to 79 per cent and averaged 40 ; (2) miscellaneous mortality of larvae, which averaged 45, 19, and 26 per cent in the first, second, and third instars, respectively; (3) starvation; and

(4) spotty and discontinuous occurrence of host tree.

In the Maritime Provinces P. geniculata fluctuates considerably in numbers in response to climatic and biotic control factors, but it lacks adequate density-dependent control factors.

Its scattered food supply seems to be the ultimate limiting factor.

The introduction of parasites, predators or disease might be beneficial. APPENDIX Appendix A

Report Fora for £. geniculata Infestations.

Date

Location ______County ______Prov.

Grid ______Forest District ______

Obse r v e r ______Address______

Tree Species (Amoricon or European mountain ash)

Note: Please collect and press at least one compound leaf for verifi­ cation of identification (a third species, Sorbua decora.is present in some areas of the Marltlaes). Approx. size: D.B.H. ______Height ______

Isolated trees ______Groups or stands ______

Trees densely shaded ______Moderately shaded _____ Open groan _

Flowers: Light ______M e d i u m ______Heavy ______

Evenly distributed ______Mostly in upper crown ______

Mostly in middle crown ______Mostly in lower crown ______

Eggs present ? ______Note: The eggs are inserted between the epidermal layers around the edges of the leaflets. They are more easily seen when the leaf is turned over. In central H. B. eggs of the first generation are usually found from June 19-30 and those of the seoond generation from August 20 - September 3. Leaves containing eggs should be oollected and sent to the laboratory as soon as possible. The petiolar ends of such leaves should be wrapped in moist absorbent cotton and the leaf placed in a cellophane bag (stapled). If the egg-bearing leaf is not shaken, one may find such egg predators as stink bugs, beetles, or other insects feeding on the eggs.

Larvae present Larvae absent Larvae feeding singly . or in colonies Larvae feeding on: Outer leaf clusters ______Inner leaf clusters (Apices of branches) Head capsules of larvae: Black Yellow ______

Defoliation: Trace to 20 per cent _____ 30 - 60 per cent ______Over 70 per cent . Defoliation mostly in vertical levels from top down as follows: A. _____ B. C.______D.______Damage: (a) Normal branches and shoots all over orown ______(b) Few dead branches and shoots in crown levels: A.. B# ______C.______D.__ (c) Half of branches and shoots dead by crown levels: A., B.______C.______D •____ (d) Whole tree dead 148

Appendix Table 1

Head Capsule Measurements by Instars of■ 451 £. geniculata Larvae,

' "?'■ ■ i^r , . v : , u s . : : , Inotar I Instar II . Instar III Instar IV . Instar V Size Mo.______Size No.______Size Ho. _____ Size No. Size No.

0.462 1 0.624 1 0.956 1 1.301 1 1.716 1 0.465 1 0.630 1 0.967 3 1.312 1 1.729 3 0.468 1 0.641 1 0.972 3 1.323 1 1.742 2 0.470 3 0.644 1 0.977 3 1.328 2 1.754 5 0.473 7 0.650 2 0.983 2 1.339 5 1.767 8 0.476 9 0.652 2 0.988 1 1.345 3 1.780 10 0.479 8 0.661 2 0.999 1 1.350 8 1.793 3 0.482 4 0.664 3 1.004 2 1.355 6 1.806 17 0.484 5 0.666 4 1.010 4 1.361 1 1.819 11 0.490 2 0.669 7 1.015 7 1.366 2 1.832 1 0.493 3 0.672 2 1.021 6 1.372 2 1.845 1 0.496 8 0.675 5 1.026 22 1.382 2 0.498 7 0.678 2 1.031 8 1.388 3 0.501 7 0.680 2 1.037 12 1.393 9 0.504 14 0.686 2 1.042 3 1.399 4 0.507 8 0.689 1 1.048 4 1.404 8 0.510 4 0.692 2 1.053 3 1.409 6 0.512 4 0.694 5 1.058 6 1.415 4 0.518 3 0.697 9 1.064 4 1.420 4 0.524 1 0.700 8 1.069 2 1.426 2 0.526 1 0.703 3 1.075 2 1.431 2 0.706 2 1.080 1 1.436 3 0.708 2 1.085 3 1.442 2 0.717 1 1.096 1 1.447 3 0.725 3 1.453 5 0.728 1 1.458 6 1.463 5 1.469 2 1.474 1 1.480 1 1.496 2 1.507 2 1.512 2

Totals 101 74 104 110 62 Appendix Table 2

Number of Flowers Recorded on S. aucut>aria by Tree and Crown Level in 1955.

Level AB C D T otal Tree

1 59 45 43 22 169

2 10 1 2 0 13

3 30 32 39 20 121

4 23 42 32 26 123 T otal 122 120 116 68 426

Analysis of Variance

Source of Degrees of Sums of Mean v aria tio n freedom squares square F P

Correction facto r 1 11342 tm tm

Trees 3 3283 1094 14*99** < .0 1

Levels 3 499 166 2.27 > .1 0 ,< .2 0

Trees x levels 9 658 73 — —

T otal 16 15782

•k* Significant within 1 per cent level 150

Appendix Table 3

Number of Flowers Recorded on S. aucuparia by Tree and Crown Quadrant in 1955.

Quadrant N E S W T o ta l T ree 1 u 46 46 33 169

2 3 1 6 3 13

3 35 25 32 29 121

4 30 21 32 40 123

T o ta l 112 93 116 105 426

Analysis of Variance

S ource o f Degrees of Sums o f Mean v a r ia tio n freedom sq u a re s sq u are F P C o rre c tio n f a c t o r 1 11342 __ — ....

T re es 3 3283 1094 34.19** < . 0 1

Q uadrants 3 76 25 0 .7 8 > . 2 0

T re e s x q u ad ran ts 9 291 32 —

T o ta l 16 14992

■a* Significant within 1 per cent level 151

Appendix Table 4

Differences in Numbers of Flowers on S. aucunaria Between th e CXiter and In n e r Crown by L evels in 1955.

L evel A B C D T o ta l T ree 1 - 5 - 1 -1 - 4 -11

2 - 2 - 1 -2 0 - 5

3 -1 4 - 4 -1 14 - 5

4 - 9 -12 -8 2 -2 7

T o ta l -30 -18 -1 2 12 -48

Analysis of Variance

Source of Degrees of Sums o f Mean variation freedom sq u ares square F F

Radial distance 1 144 — 5.33 > .1 0 ,< .2 0

R a d ia l distance x trees 3 81 27 0 .8 2 > . 2 0

R a d ia l distance x levels 3 234 78 2.36 > .1 0 ;< .2 0

Radial distance x trees x levels 295 33

T o ta l 16 754 152

Appendix Table 5

D ifferences in Numbers of Flowers on S. aucunaria Between the Outer and Inner Crown by Quadrants in 1955.

Quadrant N E S W T o tal Tree ■ 1 -2 -4 0 - 5 -11

2 -3 -1 -2 1 - 5

3 -5 -3 6 - 3 - 5

4 -6_ -3 -8 -30 -27

T otal -16 -11 ~4 -17 -48

Analysis of Variance

Source of Degrees of Sums of Mean variation freedom squares square F P

Radial distance 1 144 — 5.33 >.10j<*20

R adial distance x trees 3 81 27 2.45 > .10;< *20

Radial distance x quadrants 3 26 9 0.82 > .2 0

Radial distance x trees x quadrants J? _97 11

T o tal 16 348 Appendix Table 6 Average Number of P. Larvao per leaf Cluster Collected from Eight Leaf Clusters at Each Crown level (A, B, C, D, from top down) and in Each Crown Quadrant (N, E, S, V) on Four European Mountain Ash Trees at Two Sampling Periods. Fredericton, N. B. 1954*

______Efrirt IflmJ- pappjigg______Second larval sampling Tree Quad- ______Level______Level______no. rant ABCD SX XA B CDSX X 1 N 0.0 0.0 0.0 18.38 18.38 4.60 0.0 0.0 0.12 0,0 0.12 0.03 E 0.0 0.0 0.0 5.00 5.00 1.25 0.0 8.12 0.62 30.12 38.86 9.72 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 W 0.0 0.0 0.0 0.0 0.0 0.0 0.12 0.0 0.75 0.12 0.99 0.25 s x 0.0 0.0 0.0 23.38 23.38 — 0.12 8.12 1.49 30.24 39.97 — X 0.0 0.0 0.0 5.84 — 1.46 0.03 2.03 0.37 7.56 -- 2.50 2 N 0.0 0.0 0.0 11.62 11.62 2.90 0.0 0.12 0.0 0.0 0.12 0.03 E 0.75 2.25 9.62 0.12 12.74 3.18 0.0 0.88 4.38 0.25 5.51 1.38

S 0.0 0.0 11.88 3.88 15.76 3.94 0.0 0.0 0.0 0.88 0.88 0.22 153 w 0.0 0.0 0.0 8.62 8.62 2.16 0.0 0.0 0.25 0.0 0.25 0.06 sx 0.75 2.25 21.50 24.24 48.74 — 0.0 1.00 4.63 1.13 6.76 — X 0.19 0.56 5.38 6.06 -- 3.04 0.0 0.25 1.16 0.28 — 0.42 3 N 0.0 0.0 0.0 15.38 15.38 3.84 0.0 0.0 0.0 0.75 0.75 0.19 E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.38 26.75 28.13 7.03 S 0.0 0.0 0.0 0.25 0.25 0.06 0.0 0.0 0.0 0.0 0.0 0.0 f 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.12 0.12 0.03 SX 0.0 0.0 0.0 16.13 16.13 — 0.0 0.0 1.38 27.62 29.00 — X 0.0 0.0 0.0 4.03 — 1.01 0.0 0.0 0.34 6.90 m m 1.81 A N 0.0 0.25 2.62 8.88 11.75 2.94 0.0 1.00 0.0 0.0 1.00 0.25 E 21.13 10.00 1.00 26.12 58.24 14*56 0.0 0.0 2.00 0.0 2.00 0.50 3 0.0 0.0 6.12 0.0 6.12 1.53 0.0 1.25 0.0 1.25 2.50 0.62 1 0.0 0.0 0.0 13.00 13.00 3.25 0.0 0.0 0 .0 0.0 0.0 0.0 sx 21.13 10.25 _ 9.74 . 48.00 89.11 _ 0.0 2.25 2.00 1.25 5.50 — X 5.28 2.56 2.44 12.00 — 5.57 0.0 0.56 0.50 0.31 0.34 All tre e s SX 21.87 12.50 31.24 111.75 177.36 — 0.12 11.37 9.50 60.2A 81.23 — X 1.37 0.78 1.95 6.96 — 2.77 0.01 0.71 0.59 3.76 — 1.27 Appendix Table 7 Average Number of £. geniculata Larvae per Leaf Cluster Collected from Four Leaf Clusters in the Outer Crown and from Four Leaf Clusters in the Inner Crown at Each Crown Level (A, B, C, D, from top down) and in Each Crown Quadrant (N, E, S, W) on Four European Mountain Ash Trees at the First Larval Sampling. Fredericton, N. B. 1954.

A B C D SX X Tree Quad­ Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner no.- rant crown crown crown crown crown crown crown crowi crown crown .crown crown

1 N 0.0 0.0 0.0 0.0 0.0 0.0 36.75 0.0 36.75 0.0 9.19 0.0 E 0.0 0.0 0.0 0.0 0.0 0.0 10.00 0.0 10.00 0.0 2.50 0.0 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 w 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 s x 0.0 0.0 0.0 0.0 0.0 0.0 46.75 0.0 46.75 0.0 — X 0.0 o.o 0.0 0.0 0.0 0.0 11.69 0.0 — — 2.92 0.0 2 N 0.0 0.0 0.0 0.0 0.0 0.0 23.25 0.0 23.25 0.0 5.81 0.0 E 1.50 0.0 4.50 0.0 19.25 0.0 0.0 0.25 25.25 0.25 6.31 0.06 S 0.0 0.0 0.0 0.0 23.75 0.0 3.75 4.00 27.50 4.00 6.38 1.00 W 0.0 0.0 0.0 0.0 0.0 0.0 17.00 0.25 17.00 0.25 4.25 0.06 SX 1.50 0.0 4.50 0.0 43.00 0.0 44.00 4.50 93.00 4.50 — X 0.38 0.0 1.12 0.0 10.75 0.0 11.00 1.12 —— 5.81 0.2S 3 H 0.0 0.0 0.0 0.0 0.0 0.0 30.75 0.0 30.75 0.0 7.69 0.0 E 0.0 0.0 0.0 o.o 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 S 0.0 0.0 0.0 0.0 0.0 0.0 0.50 0.0 0.50 0.0 0.12 0.0 V 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 s x 0.0 0.0 0.0 0.0 0.0 0.0 31.25 0.0 31.25 0.0 — — X 0.0 0.0 o.o 0.0 0.0 0.0 7.81 0.0 — — 1.95 0.0 4 N 0.0 0.0 0.0 0.50 5.25 0.0 17.75 0.0 23.00 0.50 5.75 0.12 E 29.50 12.75 20.00 0.0 0.0 2.0 43.75 8.5 93.25 23.25 23.31 5.81 S 0.0 0.0 o.o 0.0 12.25 0.0 0.0 0.0 12.25 0 .0 3.06 0 .0 V 0.0 0 .0 0 .0 0 .0 0 .0 0 .0 25.75 0.25 25.75 0.25 6.44 0.06 SI 29.50 12.75 20.00 0.50 17.50 2.00 87.25 8.75 154.25 24.00 —— X 7.38 3.19 5.00 0.12; 4.38 0.50 21.81 2.19 — — 9.64 1.50

All treee SZ 31.00 12.75 24.50 0.50 60.50 2.00 209.25 13.25 325.25 28.50 — a m X 1.94 0.80 1.53 0.03 3.78 0.12 13.08 0.83 — — 5.08 0.44 Appendix Table 3 Average Nuober of £. geniculata Larvae per Leaf Cluster Collected trm Four Leaf Clusters In the Outer Crown and Aron Four Leaf Clusters In the Inner Grown at Eaoh Crown Level (A, B, C, D, Aram top down) and in Each Crown Quadrant (H, E, S, V) on Four European Mountain Ash Treea at the Seoond Larval Sanpling. Fredericton, N. B. 1954.

Level A B C D SX X Tree Quad­ Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner no. rant crown crown crown crown crow crown crown crown crow crown c r o w crown 1 H 0.0 0.0 0.0 0.0 0.0 0.25 0.0 0.0 0.0 0.25 0.0 0.06 E 0.0 0.0 16.25 0.0 0.0 1.25 31.25 29.00 47.50 30.25 11.88 7.56 S 0.0 0.0 0.0 0.0 0.0 0,0 0.0 0.0 0.0 0.0 0.0 0.0 w 0.0 0.25 0.0 0.0 0.0 1.50 0.0 0.25 0.0 2.00 0.0 0.50 s x 0.0 0.25 16.25 0.0 0.0 3.00 31.25 29.25 47.50 32.50 —— X 0.0 0.06 4.06 0.0 0.0 0.75 7.81 7.31 — — 2.97 2.03 2 N 0.0 0.0 0.25 0.0 0.0 0.0 0.0 0.0 0.25 0.0 0.06 0.0 E 0.0 0.0 0.0 1.75 3.75 5.00 0.25 0.25 4.00 7.00 1.00 1.75 S 0.0 0.0 0.0 0.0 0.0 0.0 1.75 0.0 1.75 0.0 0.44 0.0 1 0.0 0.0 0.0 0.0 0.25 0.25 0.0 0.0 0.25 0.25 0.06 0.06 SX 0.0 0.0 0.25 1.75 4.00 5.25 2.00 0.25 6.2 5 7.25 — — X 0.0 0.0 0.06 0.44 1.00 1.31 0.50 0.06 — — 0.39 0.45 3 N 0.0 0.0 0.0 0.0 0.0 0.0 0.25 1.25 0.25 1.25 0.06 0.31 E 0.0 0.0 0.0 0.0 2.75 0.0 53.50 0.0 56.25 0.0 14.06 0.0 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 T 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.25 0.0 0.25 0.0 0.06 SX 0.0 0.0 0.0 0.0 2.75 0.0 53.75 1.50 56.50 1.50 —— ■ X 0.0 0.0 0.0 o.o 0.69 0.0 13.44 0.38 — — 3.53 0.99 4 N 0.0 0.0 2.00 0.0 0.0 0.0 0.0 0.0 2.0C 0.0 0.50 0.0 E 0.0 0.0 0.0 0.0 4.00 0.0 0.0 0.0 4.00 0.0 1.0C 0.0 S 0.0 0.0 1.00 1.50 0.0 0.0 0.50 2.00 1.50 3.50 0.38 0.38 w 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 s x 0.0 0.0 3.00 1.50 4.00 0.0 0.50 2.00 7.50 3.50 — — X 0.0 0.0 0.75 0.38 1.00 0.0 0.12 0.50 0.47 0.22 All trees SX 0.0 0.25 19.50 3.25 10.75 8.25 87.50 33.00 117.75 44.75 — — X 0.0 0.02 1.22 0.20 0.67 0.52 5.47 2.06 __ — 1.84 0.70 Appendix Table 9 Avenge Number of f » Larvae per Leaf Cluster Collected from Eight Leaf Clusters a t Each Crown Level (A, B, C, D, from top down) anl In Each Crown Quadrant (N, E, 3, V) on Four European fountain Adi Trees a t Two Sampling Periods. Fredericton, U. B, 1955,

1_r' r,m First larval samel inr Tree Quad­ Level L e no. rant A B C D . _ sx Z A B C D SZ Z 1 N 16.25 0.0 0.0 0.0 16.25 A.06 0.0 0.0 0.0 0.0 0.0 0.0 E 11.00 0.0 1.75 7.25 20.00 5.00 0.0 0.0 1.25 0.0 1.25 0.31 S 11.88 0.0 15.75 12.50 AO.13 10.03 0.0 0.38 0.75 5.88 7.01 1.75 « 0.0 0.0 1A.88 1.12 16.00 A.00 0.0 0.0 0.0 5.00 5.00 1.25 SZ 39.13 0.0 32.38 20.87 92.38 — 0.0 0.38 2.00 10.88 13.26 — z 9.78 0.0 8.10 5.22 5.77 0.0 0.10 0.50 2.72 — 0.83 2 H 0.0 0.0 9.62 7.38 17.00 A. 25 0.0 0.0 0.0 0.0 0.0 0.0 E 0.25 0.12 16.12 0.50 16.99 A. 25 0.0 0.0 0.38 0.0 0.38 0.10 S 0.25 8.38 A.62 2.25 15.50 3.88 0.0 0.0 0.0 C.0 0.0 0.0 w 0.0 0.0 0.62 9.75 10.37 2.59 0.0 2.88 1.25 0.50 A.63 1.16 H VJl SZ 0.50 3.50 30.98 19.88 59.86 — 0.0 2.88 1.63 0.50 5.01 — ON z 0.12 2.12 7.7A A.97 -- 3.7A 0.0 0.72 0.A1 0.12 — 0.31 3 N 0.0 0,0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 1.88 1.88 0.A7 E 0.0 0.0 0.0 11.75 11.75 2.9A 0.0 0.0 0.0 2.50 2.50 0.62 S 0.0 0,0 0.0 0.25 0.25 0.06 0.0 0.0 0.0 0.38 0.38 0.10 T 0.0 0.0 3.75 0.0 8.75 .7.19 0.0 0.0 0.0 0.0 0.0 0.0 SZ 0.0 0.0 3.75 12.00 20.75 — 0.0 0.0 0.0 A.76 A.76 m m z 0.0 0.0 2.19 3.00 — 1.30 0.0 o.o 0.0 1.19 — 0.30 A B 0.0 o.o 0.12 3.50 3.62 0.90 0.0 o.o 0.12 0.0 0.12 0.03 E 0.0 0.0 0.0 13.50 13.50 3.38 0.0 0.0 0.0 2.38 2.38 0.60 3 0.0 0.0 0.0 2.25 2.25 0.56 0.0 0.0 0.0 1.75 1.75 O.AA V 0.0 o.o 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SZ 0.0 0.0 0.12 19.25 19.37 a v 0.0 0.0 0.12 A.13 A.25 — z 0.0 0.0 0.03 A.81 — 1.21 0.0 0.0 0.03 1.03 — 0.26 A ll tre e s SX 39.63 8.50 72.23 72.00 192.36 — 0.0 3.26 3.75 20.27 27.28 — z 2. AS 0.53 A.51 A.50 3.00 0.0 0.20 0.23 1.27 — 0.A3 Appendix Table 10 Average Number of £. geniculata Larvae per Leaf Cluster Collected from Four Leaf Clusters in the Outer Crown and from Four Leaf Clusters in the Inner Crown at Each Crown Level (A, B, C, D, from top down) and in Each Crown Qjadrant (N, E, S, IT) on Four European Mountain Ash Trees at the First Larval Sampling. Fredericton, N. B. 1955.

Level A B C _ .. D SX Z Tree Quad­ Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner no. rant crown crown crown crown crown crown crown crown crown crown crown crown 1 N 32.50 0.0 0.0 0.0 0.0 0.0 0.0 0,0 32.50 0.0 8.12 0.0 E 15.00 7.00 0.0 0.0 3.50 0.0 14.25 0.25 32.75 7.25 8.19 1.81 S 23.75 0.0 0.0 0.0 27.00 4.50 25.00 0.0 75.75 4.50 18.94 1.12 IT 0.0 0.0 0.0 0.0 29.50 0.25 0.0 2.25 29.50 2.50 7.38 0.62 SZ 71.25 7.00 0.0 0.0 60.00 4-75 39.25 2.50 170.50 14.25 —— Z 17. SI 1.75 0.0 0.0 15.00 1.19 9.31 0.62 —— 10.66 0.89 2 N 0.0 0.0 0.0 0.0 17.50 1.75 14.75 0.0 32.25 1.75 8.06 0.44 E 0.0 0.50 0.0 0.25 1.50 30.75 0.0 1.00 1.50 32.50 0.38 8.12 S 0.50 0.0 16.75 0.0 9.00 0.25 0.0 4.50 26,25 4.75 6.56 1.19 w 0.0 0.0 0.0 0.0 1.25 0.0 19.50 0.0 20.75 0.0 5.19 0.0 SZ 0.50 0.50 16.75 0.25 29.25 32.75 34.25 5.50 80.75 39.00 — — z 0.12 0.12 4.19 0.06 7.31 8.19 8.56 1.38 — — 5.05 2.44 3 N 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0 JO E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 23.50 0.0 23.50 0.0 5.88 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.50 0.0 0.50 0.0 0.12 w 0.0 0.0 0.0 0.0 16.50 1.00 0.0 0.0 16.50 1.00 4.12 0.25 SZ 0.0 0.0 0.0 0.0 16.50 1.00 0.0 24.00 16.50 25.00 — — z 0.0 0.0 0.0 0.0 4.12 0.25 0.0 6.00 —— 1.03 1.56* 4 N 0.0 0.0 0.0 0.0 0.0 0.25 7.00 0.0 7.00 0.25 1.75 0.06 E 0.0 0.0 0.0 0.0 0.0 0.0 0.0 27.00 0.0 27.00 0.0 6.75 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 4.50 0.0 4.50 0.0 1.12 V 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 SZ 0.0 0.0 0.0 0.0 0.0 0.25 7.00 31.50 7.00 31.75 — — X 0.0 0.0 0.0 0.0 0,0 o.o6 1.75 7.88 — — ' O . u 1.98 All trees SZ 71.75 7.50 16.75 0.25 105.75 38.75 80.50 63.50 274.75 110.00 — a* m X 4*48 0.47 1.05 0.02 6.61 2.42 5.03 3.97 — — 4.29 1.72 Appendix Table 11 Average Niafrer of £. BanlgdlAta Larvae per Loaf Cluster Collected froa Four Leaf Clusters in the Outer Crown and froa Four Leaf Clusters in the Inner Groan a t Eaoh Crown Level (A, B, C, D, fTon top d o n ) and in Each Crown Quadrant (N, E, S, V) on Four European Mountain Adi Trees at the Seoond Larval Stapling. Fredericton, N. B. 1955*

Level A B C D _ SX X Tree Quad­ Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner Outer Inner no* rant orown crown crown crown crown crown crown orown crown crown crown orown 1 » 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 E 0.0 0.0 0.0 0.0 2.50 0.0 0.0 0.0 2.50 0.0 0.62 0.0 S 0.0 0.0 0.0 0.75 0.0 1.50 0.25 11.50 0.25 13.75 0.06 3.44 w 0.0 0.0 o.o 0.0 0.0 0.0 9.25 0.75 9.25 0.75 2.31 0.19 SZ 0.0 0.0 0.0 0.75 2.50 1.50 9.50 12.25 12.00 14.50 —— X 0.0 0.0 0.0 0.19 0.62 0.38 2.38 3.06 — — 0.75 o . 9 i : 2 N 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ' E 0.0 0.0 0.0 0.0 0.75 0.0 0.0 0.0 0.75 0.0 0.19 0 JO S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 I -0.C 0.0 5.75 0.0 0.25 2.25 1.00 0.0 7.00 2.25 1.75 0.56 SX 0.0 0.0 5.75 0.0 1.00 2.25 1.00 0.0 7.75 2.25 — X 0.0 0.0 1.44 0.0 0.25 0.56 0.25 o.o —— 0.48 o . u 3 N 0.0 0.0 0.0 0.0 0.0 0.0 2.00 1.75 2.00 1.75 0.50 0.44 E 0.0 0.0 0.0 0.0 0.0 0.0 3.50 1.50 3.50 1.50 0.88 0.38 S 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.75 0.0 0.75 O.o 0.19 V 0.0 0.0 0.0 0.0 0,0 0.0 0.0 0.0 0.0 0.0 0.0 04) sx 0.0 0.0 0.0 0.0 0.0 0.0 5.50 4.00 5.50 4.00 — — X 0.0 0.0 0.0 0.0 0.0 0.0 1.38 1.00 — w 0.34 0.25 4 H 0.0 0.0 0.0 0.0 0.25 0.0 0.0 0.0 0.25 0.0 0.06 0.0 E 0.0 0.0 0.0 0.0 0.0 0.0 A. 75 0.0 4.75 0.0 1.19 0J0 s 0.0 0.0 0.0 ■0.0 0.0 0.0 3.25 0.25 3.25 0.25 0.81 0.06 V 0.0 0.0 0.0 0.0 0.0 0,0 0.0 0.0 0.0 0.0 0.0 0.0 sx 0.0 0.0 0.0 0.0 0.25 0.0 8.00 0.25 8.25 0.25 — — A 0.C 0.0 0.0 0.0 0.06 0.0 2.00 0.06 — — 0152 0.02 All trees SZ 0.0 0.0 5.75 0.75 3.75 3.75 24.00 16.50 33.50 21.00 —— X 0.0 0.0 0.36 0.05 0.23 0.23 1.50 1.03 —— 0.52 0.33 159

Appendix Table 12

Number of P. geniculata Larvae Recorded on S. aucuparla by Tree and Crown Quadrant in 1954- and 1955.

Quadrant N E S ______W______T otal Tree 1954 1955 1954 1955 1954 19 55 1954 1955 1954 1955 1 148 130 351 170 0 377 8 168 507 845

2 94 136 146 139 133 124 71 120 444- r r r 519.

3 129 15 225 114 2 5 1 70 357 204

4 102 J O 482 127 J 9 J 2 104 0 757 189 T otal 473 311 1204 550 204 538 184 358 2065 1757

Analysis of Variance

Source Degrees Sums of Mean of o f gquAres squares F P v aria tio n freedom 1954 1955 1954 1955 1954 1955 1954 1955 Correction facto r 1 266514 192940

Trees 3 22157 7 2 2 a 7386 24080 1.03 4.98* >.20 >.01^335

Quadrants 3 170690 11267 56897 3756 7.97** 0.78 <.01 >.20

Trees x quadrants _9 64266 43497 7141 4833

Total 16 523627 319945

# Significant within 5 per cent level ## Significant within 1 per cent level 1 6 0

Appendix Table 13

Differences In Numbers of P. geniculata Larvae Between the Outer and Inner Grown by Levels in 1954- and 1955.

Level A B C D Total T ree 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955 1 -1 257 65 -3 -12 225 195 136 247 615

2 6 0 12 89 167 -19 165 119 350 189

3 0 0 0 0 11 62 334 -90 345 -28

4 67 0 84 0 78 0 308 -67 537 ^67 T o ta l 72 257 161 86 244 268 1002 98 1479 709

Analysis of Variance

Source D egrees Sums o f Mean o f o f sauares squares F P variation freedom 1954 1955 1954 1955 1954 1955 __ 1954 _ 1955 R a d ia l d is ta n c e 1 136715 31418 — — 37.25**1.28 < . 0 1 > . 2 0 R a d ia l d is ta n c e X tr e e s 3 1 1 0 1 1 73387 3670 24462 0.89 3.55 > . 2 0 > jO 5 ; < .1 0 R a d ia l d is ta n c e X le v e ls 3 136946 7300 45649 2433 11.05^0.35 < . 0 1 > .2 0 R a d ial d is ta n c e X t r e e s x le v e ls _9 37187 61950 4132 6883

T o ta l 16 321859 174055

Significant within 1 per cent level 1 6 1

Appendix: Table 14-

Differences in Numbers of P. geniculata Larvae Between the Outer and Inner Crown by Quadrants in 1954 and 1955*

Quadrant N E W Tgt&L Tree 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955 1 146 130 109 112 0 231 -8 142 247 615

2 94 122 88 -121 101 86 67 102 350 189

3 119 1 225 -86 2 -5 -1 62 345 -28

4 98 28 296 -89 J i j - 6 102 0 537 z £ L T o tal 457 281 718 -184 144 306 160 306 1479 709

Analysis of Variance

Source Degrees Sums of Mean o f o f ^.gflUflEgg, ,.§fl3KffSg. variation freedom 1954 1955 1954 1955 1954 1955 1954 1955 R adial d ista n c e 1 136715 31418 — — 37.25**!.28 <.01 >.20 R adial d ista n c e x tr e e s 3 11011 73387 3670 24462 0.94 10.66** >.20 <.01 R adial d ista n c e x quadrants 3 55962 43604 18654 14535 4.80* 5.98^JL j<;05>D1;<.05 R adial d ista n c e x tre e s x quadrants 9 34939 21892 3882 2432 Total 16 238627 170301

* Significant within 5 per cent level Significant within 1 per cent level 1 6 2

Appendix Table 15

Differences in Numbers of P. geniculata Larvae Between F irst and Second Samplings by Levels in 1954- and 1955.

L evel A B C D T o ta l T ree 1954 1955 1954- 1955 1954 1955 1954 1955 1954 J-255 1 -1 313 -65 -3 -12 243 -55 80 -133 633

2 6 4 10 45 135 235 185 155 336 439

3 0 0 0 0 -11 70 -96 58 -107 128

4 169 _ .o 64 _0 62 0 374 121 669 121 T o ta l 174 317 9 42 174 54S 408 414 765 1321

Analysis of Variance

Source D egrees Sums o f Mean of of squares squares variation freedom 1954 1955 1954 1955 1954 1955 1954 1955 Sam pling d a te 1 36576 109065 — — 0.99 6.96 >.20 >.05,-CIO Sam pling date x trees 3 110823 4TO44 36941 15681 4.26* 1 .8 3 >.01,<.05 > .2 0 Sam pling d a te x le v e ls 3 20198 34423 6733 11474 0.78 1.34 >.20 >.20 Sam pling date x trees x le v e ls 9 78098 77091 8678 8566

T o ta l 16 245695 267623

* Significant within 5 per cent level 163

Appendix Table 16

Differences in Numbers of £« geniculata Larvae Between F irs t and Second Samplings 67 Quadrants in 1954- and 1955*

Quadrant N EW Total Tree 1954 1955 1954 1955 1954 1955 1954 1955 1954 1955 1 146 130 -271 150 0 265 -8 88 -133 633

2 92 136 58 133 119 124 67 46 336 439

3 117 -15 -225 74 2 -1 -1 70 -107 128

4 J 6 28 450 J 9 _29 104 0 669 121 Total frr*441 279 12 446 150 392 162 204 765 1321

Analysis of Variance

Source Degrees Sums of Mean of of sauares sauares F P variation freedom 1954 1955 1954 1955 1954 1955 1954 1955 Sampling <3 ir\ 0 1 A — date 1 36576 109065 — -- 0.99 6.96 >.20 1 Sampling date x trees 3 110823 47044 369a 15681 1.39 5*57* >.20 >.01,<05 Sampling date x quadrants 3 24266 8944 8089 2981 0.30 1.06 >.20 >.20 Sampling date x trees x quadrants 9 239506 25316 26612 2813

Total 16 411171 190369

* Significant within 5 per cent level 164

Appendix Table 17

Differences in Numbers of P. eeniculata Larvae Between th e Outer and In n er Crown in D iffe re n t Sampling Periods by Levels in 1954 and 1955.

Level A BCD T o tal Tree 1954 1955 1954 1955 1954 1955 1954 :L955 1954 19 £5 1 1 257 -65 3 12 217 179 158 127 635

2 6 0 24 43 177 -9 151 111 358 145

3 0 0 0 0 -11 62 -84 ■-102 -95 -40

4 67 0 72 _0 46 -2 320 ■" 3 S 505 -131 T o tal 74 257 31 46 224 268 566 38 895 609

Analysis of Variance

Source Degrees Sums o f Mean of o f sauares sauares FP variation freedom 1954 1955 1954 1955 1954 1955 1954 1955 R ad ial distance x sam pling date 1 50064 23180 — 2.89 0.79 XL0$<.20 >.20 R x S x T 3 52022 87573 17341 29191 2.36 4 .35*>.10j<. 20>.01,<£5 R x S x L 3 44178 12178 14726 4059 2.00 0.60 >.00;<.20 >.20 R x S x T x L _9 66255 60324 7362 6703

T o tal 16 212519 183255

# Significant within 5 par cent level 165

Appendix Table 18

Differences in Numbers of P. genlculata Larvae Between the Outer and Inner Crown in Different Sampling Periods by Quadrants in 1954 and 1955*

Quadrant N E S W T otal Tree 1954 1955 1954 19 55 1954 1955 1954 ltf 5 1954 1955

1 148 130 -29 92 0 339 8 74 127 635

2 92 122 112 -127 87 86 67 64 358 145

3 127 -1 -225 -1J02 2 1 1 62 -95 -40 I S 4 82 26 264 i J 7 -30 102 0 505 -131

T otal 449 277 122 -264 146 396 178 200 895 609

Analysis of Variance

Source Degrees Sums of Mean of of Bouares squares F P v a ria tio n freedom 1954 1955 1954 __ 1955 1954 1955 1954 1955

R x S 1 50064 23180 — — 2.89 0.79 >.10j<.2O >.20 R x S x T 3 52022 87573 1 7 3 a 29191 1.67 5.6L* >.20 >.01;C05 R x S x Q 3 17307 62630 5769 20877 O .5 6 4 .01* >.20 >.01;<.05 R x S x T x Q _9 93314 46838 10368 5204 T otal 16 212707 2202a

* Significant within 5 per cent level 1 6 6

Appendix Table 19

Average June-July Rainfall In Inches for Six Stations in Southern New Brunswick from 1936 to 1955.

Year Rainfall Year Rainfall

1936 2.62 1946 1.56

1937 2.62 1947 4.59

1938 4.29 1948 3.67

1939 2.94 1949 1.80

1940 2.93 1950 3.38

1941 2.96 1951 3.44

1942 2.48 1952 2.54

1943 4.63 1953 3.65

1944 3.10 1954 4.64

1945 3.54 1955 2.03 LITERATURE CITED

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I, Robert Shirley Forbes, was born in Moncton, New

Brunswick, Canada, March 14> 1921. I received ay secondary school

education in the public schools of Moncton, and ay undergraduate

training at the University of New Brunswick in Fredericton, from

which I received the degree of Bachelor of Science in Forestry in

1944* I received the Master of Science degree from the same

University in 194-9* I was awarded the C. H. L. Jones Forestry

Scholarship for graduate work for the academic year 1947-4&* and

during the same year, assisted Professor N. R. Brown, I was

appointed University Scholar at Ohio State University for 1953-54>

where I specialized in Entomology in the Department of Zoology and

Entomology. I assisted in th is Department fo r two quarters in

1954-55 while completing the residence requirements for the degree

Doctor of Philosophy. Since that time I have been employed as a

Research Officer with the Forest Biology Division, Research Branch,

Canada Department of Agriculture a t Fredericton.

176