A SURVEY OF MICROORGANISMS ASSOCIATED WITH THE PINE FALSE WEBWORM ACANTHOLYDA ERYTHROCEPHALA (L.) (PAMPHILIIDAE: HYMENOPTERA) File Report No. 17. J. M. BURKE Forest Pest Management Institute Canadian Forestry Service Sault Ste. Marie, Ontario This report may not be copied and/or distributed without the express- consent of: Director Forest Pest Management Institute Canadian Forestry Service P.O. Box 490 Sault Ste. Marie, Ontario P6A 5M7 TABLE OF CONTENTS Page INTRODUCTION 1 MATERIALS AND METHODS 3 RESULTS AND DISCUSSION 3 REFERENCES 6 Tables: I. Diagnosis of A. erythrocephala larvae collected 1979- 1981 in Southern Ontario 8 II. A. erythrocephala collected in Southern Ontario by Forest Insect and Disease Survey - Great Lakes Forest Research Centre ..... 9 III. Number of eggs laid per red pine needle by A. erythrocephala 10 IV. Cross infection tests with A. erythrocephala as host insect 11 A SURVEY OF MICROORGANISMS ASSOCIATED WITH THE PINE FALSE WEBWORM ACANTHOLYDA ERYTHROCEPHALA (L.) (PAMPHILIIDAE: HYMENOPTERA) INTRODUCTION The pine false webworm Acantholyda erythrocephala L. is an introduced species to North America and was first recorded in Pennsylvania in 1925. It was reported to occur from Connecticut to New Jersey and Pennsylvania in the United States and in New Brunswick, Canada. The preferred hosts are white and red pines, but it also attacks several other pines, including Scots, Austrian, Mugho, Swiss Mountain red, and Japanese red (Eastern Forest Insects, 1972). While this publication reports the insect to be in New Brunswick, it would appear that the specimens referred to were collected in Ontario in Scarborough township, July 6, 1961 and reared at Fredericton, N.B. (Eidt and McPhee, 1963). Eidt and McPhee (1963) report this collec tion to be the first record of this European species in Canada and give a brief review of it in the United States, its host trees in the United States and its distribution in the old world. The insect is not mentioned in the Annual Reports of the Forest Insect and Disease Survey, Canadian Forestry Service, from 1941 to 1975 under the name Acantholyda erythrocephala or as Cephalcia frontalis or Cephalcia sp. with which it may be readily confused. However, Sippell and McDowall (1976) mention a webspinning sawfly, Cephalcia spp. and state that "Until recently this insect had been considered a rare, or at most an occasional, pest of pine which seems to concentrate its attack on a few trees here and there throughout pine plantations." In 1976 it caused severe defoliation in parts of several Scots pine Christmas tree plantations in Oro and Mono town ships, was common in two red pine plantations in Lindsay District and was generally more numerous than usual in a number of other red pine plantations in Southern Ontario. Howse and McDowall (1977) report that for the second consec- tive year, heavy infestations of Cephalcia spp. occurred in Scots pine plantations in Oro and Mono townships in Huronia district and new infestations of similar density were found on jack pine, red pine and Scots pine at several other locations in the district. Heavy defolia tion also occurred in the Ottawa, Minden and Parry Sound Districts. Heavy infestations of Cephalcia spp. recurred in Scots pine plantations in Oro township and moderate infestations in Mono township in 1978. Elsewhere throughout the Central Region of Ontario infesta tions were reported in several districts. A collection of adults from the Central Region was identified as Acantholyda erythrocephala L., an introduced species, reported only three times previously in Canada (McDowall and Howse, 1978). In 1979 a general increase in the population was reported and moderate to heavy infestations persisted in several locations in Huronia, Lindsay, Brockville, Ottawa, Minden and Bancroft districts with light populations in a number of locations elsewhere (McDowall and Howse, 1979). High populations of the sawfly persisted in the Central Region of Southern Ontario in 1980. While some of the older infesta tions showed some reduction in numbers, defoliation still ranged from moderate to heavy. In the Eastern Region high populations were noted in single townships, while in the Algonquin region populations and distribution of» the insects increased over 1979 (McDowall and Howse, 1980). There was little change in the distribution of the insect in 1981 but in general populations were somewhat lower than in 1980 (AppleJohn and Howse 1981). Jahn (1967) describes an outbreak of the false pine webworm in Europe that was heavily infected by a nuclear polyhedosis virus. However, while large numbers of dead larvae were observed, the out break continued at the same intensity and the area affected enlarged. There appears to be some confusion about the reported virus. Material was sent to England and they were unable to confirm the presence of virus (Dr. J. Cunningham, pers. communication). The life history of A. erythrocephala is described by Syme (1981) who also states, "In Ontario it is significant because it causes serious defoliation of pines, which are planted extensively in the province." A literature review of A. erythrocephala and its natural enemies was prepared by Carl and Kulling (1981) on behalf of the Great Lakes Forest Research Centre, Sault Ste. Marie, Ontario, as there was "increasing concern about the insect." In Europe outbreaks of the insect are rare with 10 outbreaks recorded during the last 150 years. They generally lasted 2-3 years, but one from 1964-1971 in eastern Austria, lasted 8 years. Tree mortality is rare but growth can be reduced up to 60% during prolonged periods of heavy attack. The report mentions the natural enemies, of which parasites appear to be the most important. A detailed study by C.I.B.C. in Europe of the natural enemy complex of the sawfly is being considered. MATERIALS AND METHODS A survey of pathogenic microorganisms associated with A^. erythrocephala was begun in 1979. No attempt was made to ascertain the normal flora of the insect as interest was centred on the search for pathogens only. Early collections were made when the larvae were very young or eggs were still unhatched and these were reared in the laboratory so that, if disease appeared in the population, it could be readily detected. It also provided young larvae for infection tests. A second collection was made when most larvae had dropped to the ground to overwinter in order to see if any dead or diseased larvae were left behind in the nests. Collections were made each year from a heavily infested plantation near Lakehurst in Harvey township. A lightly infested plantation in Glenelg township near Durham was also selected for yearly collections to see if disease organisms became more prevalent as the infestation developed. It would appear that the population near Durham died out rather than increasing, so another light population was selected in Oro township near Craighurst, Ontario. In addition, collections of the insect were submitted by the Forest Insect and Disease Survey, Great Lakes Forest Research Centre, from numerous districts in Southern Ontario. RESULTS AND DISCUSSION A summary of the results from collections made in the study areas is given in Table I. Fifty nests were collected in early June near Lakehurst, Ont. Four hundred and thirteen larvae from these were examined for disease and were disease free. Four nests collected near Durham were very small. Only 11 larvae were found, and these were free from disease. In early July the late collection was made. Two hundred nests were collected near Lakehurst. These contained 123 larvae, 47 of which were dead and were .free of disease. We were unable to find further nests at Durham so collected 25 at Craighurst. The seventeen larvae present were uninfected. Much the same procedure was followed in 1980 except that the late collection was made when the larvae were almost mature but had not left the nests to overwinter in the ground. Results are included in Table I. In 1981 we were unable to find larvae at Craighurst but did find a few nests at Uxbridge Forest. The results of this and our results from the plot at Lakehurst are also given in Table I. During the three year study, a total of 1975 larvae from 895 nests were examined microscopically and microorganisms were not observed. In addition, during the three years, a further 29 samples were received from the Forest Insect and Disease Survey; 469 larvae were examined and were free of disease, Table II. In conjunction with this study, we took the opportunity to examine the number of eggs per needle and the larvae per nest to see if the same pattern was being followed in Ontario as by the popula tions in Europe. Carl and Kiilling (1981) mention "eggs are laid singly or more commonly in rows of 2-8 or more on the inner side of needles." They also state "The number of eggs laid per needle is positively correlated with the needle length," but do not mention what species of pine was examined. We examined 815 red pine needles and are in general agreement with that data. The most eggs observed on one needle was 16 and that occurred only once. We found that 97.3% of the needles contained 1-8 eggs. Our data on the egg count are given in Table III. Unfortunately we did not examine Scots pine needles as well. Carl and Kiilling (1981) also mention that, "Usually the larvae are gregarious with up to 35 individuals aggregating in sausage-shaped or globular webs." In 1980 we examined 205 nests on red pine at Lakehurst and they averaged 9.3 larvae per nest. However, in 1981 a further 255 nests were examined and the average number of insects per nest was 18.0. We are unable to suggest a reason for the difference in the averages in the two years.