EUROPEAN SPRUCE SAWFLY
Gilpinia hercyniae (Hartig) -- Diprionidae
[also known as Diprion hercyniae (Hartig)]
A spruce (Picea spp.) feeding insect native to most of Europe, the European spruce sawfly was first noted as an accidental introduction in Canada in 1922 (Dahlsten & Mills 1999). By 1930 a severe outbreak was causing concern in the Gaspe Peninsula and by 1936 the sawfly threatened to devastate the spruce forests of eastern Canada by extending its range across all eastern Provinces and adjacent United States and causing severe damage over an area of more than 10,000 sq. miles (McGugan & Coppel 1962).
One of the most extensive projects undertaken in classical biological control was begun against European spruce sawfly in 1933. Gilpinia hercyniae was not at first distinguished from G. polytomum (Htg.) and the Farnham House Laboratory in England (now known as CIBC) was engaged to make large scale parasitoid collections from the latter species in Europe. Initial studies revealed that apart from the egg parasitoids, all other parasitoids develop so as to overwinter in the host cocoon. This simplified parasitoid collections in Europe to those stages of development. A team of about 30 persons collected >1/2 million cocoons of G. polytomum in Europe for shipment to Canada during 1932-40. Additionally more >1/2 million eggs and 31 million cocoons of other spruce and pine feeding sawflies were shipped to supplement the numbers of the less host specific parasitoid species available for field release (Morris et al. 1937, Finlayson & Finlayson 1958). There were 96 species of primary and secondary parasitoids obtained from these cocoon collections at the Belleville Laboratory in Canada and a multiple introduction program involving two egg parasitoids and 25 larval and cocoon parasitoids was initiated in 1933-51. The importation of a wide variety of parasitoids from diverse hosts permitted the inclusion of several sawfly pests as additional targets for some of the releases (McGugan & Coppel 1962).
The addition of an elaborate controlled environment quarantine building was made at Belleville in 1936 allowed the mass rearing of several of the imported European parasitoids. Dahlbominus fuscipennis, a gregarious ectoparasitoid of prepupae, readily attacked cocoons in the laboratory and was selected along with several other species for a massive program of mass rearing for release. The mass-rearing peaked in 1940 when a total of 221.5 million D. fuscipennis was released and by the end of the program in 1951 a total of 890 million directly imported or laboratory reared parasitoids had been liberated (McGugan & Coppel 1962).
Only 5 species of parasitoids out of 27 released became established over more than several generations, although four additional species were recovered during the years shortly after release. Three of the five species, D. fuscipennis, Exenterus amictorius (Panz.) and E. confusus Kerr, were widely established only during the outbreak and have since not been recovered from G. hercyniae. Although E. amictorius had little impact, the other two species achieved variable but appreciable levels of parasitism and have been credited with the decline of the outbreak in at least some areas. Two other parasitoids, Exenterus vellicatus Cush. and Drino bohemica Mesn., never became important until the collapse of the outbreak but have replaced the three species present during the outbreak to maintain host population at low, non-damaging densities.
The epizootic of European spruce sawfly began to decline in 1939-40, which coincided in the southern part of the range with the occurrence of a nuclear polyhedrosis virus, Borrelinavirus hercyniae. This virus is thought to have been accidentally imported and released in Canada along with the parasitoid (Dahlsten & Mills 1999). It spread rapidly to produce virus epizootics throughout most of the outbreak range and by 1943 host population densities had declined to very light infestations. Unlike other diprionid sawflies, G. hercyniae larvae are not gregarious and the rapid spread and subsequent impact of the virus was attributed to its virulence (Bird & Elgee 1957). More recent studies in the Great Britain, where G. hercyniae was accidentally introduced from the European continent in 1968, indicate that birds play an important role in virus transmission (Entwistle 1976). The importance of D. bohemica, E. vellicatus and the NPV virus in maintaining the spruce sawfly at low population densities in Canada has been inadvertently demonstrated through chemical spray treatments aimed against spruce budworm. Both in the early 1960's and again in the 1970's sawfly population levels increased immediately following the cessation of a 2-3 year spray treatment, due to the detrimental effects of the spray on natural enemies, but declined after several generations as a result of increased parasitism and the reappearance of the virus (Neilson et al. 1971, Magasi & Syme 1961, Dahlsten & Mills 1999).
Dahlsten & Mills (1999) pointed to several interesting features of this successful biological control program. First the success of the accidental introduction of the virus provides to date the most outstanding example of the use of a pathogen in classical biological control. Its ability to control the sawfly population in the absence of parasitoids has been demonstrated (Bird & Burk 1961, Entwistle 1976) and in Canada it has persisted in the forest environment since the initial introduction despite the low host densities (Magasi & Syme 1981). The multiple introduction program of parasitoids resulted in the establishment of the two more effective and specific species, despite the release of a wide range of potential competitors. However, the continuous and large scale release of poorly adapted parasitoids, which were later recovered only from other sawfly hosts, was successful in inducing significant levels of mortality prior to the introduction of the virus.
For greater detail on the hosts, natural enemies and biological control please refer to the following (Webber 1932, Morris & Cameron 1935, Morris 1937, 1942; Baird 1939, 1940; Cushman 1940, Balch et al. 1941, Peirson 1941, Reeks 1937, 1941, 1952, 1953; Peirson & Nash 1940, Wilkes 1942, Balch & Bird 1944, Daviault 1944, Dirks 1944, Briand 1949, Schaffner & Middleton 1950, Balch 1960, Griffiths 1961, Turnbull & Chant 1961, Dowden 1962, Graham & Jones 1962, Martineau 1963, Neilson & Morris 1964, McLeod & Desalliers 1966, Rose & Sippell 1966).
REFERENCES: [Additional references may be found at: MELVYL Library ]
Baird, A. B. 1939. Biological control of insect pests in Canada with special reference to the European spruce sawfly Gilpina polytoma Htg. Ent. Soc. Ontario, 70th Ann. Rept. (1939): 51-56.
Baird, A. B. 1940. A review of the spruce sawfly parasite situation. Pulp and Paper Mag., Canada. Ann. Meeting, Woodlands Sect., Canad. Pulp Assoc. Proc., Jan 1939: 43-4.
Balch, R. E. 1960. The approach to biological control in forest entomology. Canad. Ent. 92: 297-310.
Balch, R. E. & F. T. Bird. 1944. A disease of the European spruce sawfly, Gilpinia hercyniae (Htg.), and its place in natural control. Sci. Agric. (Ottawa) 25: 65-80.
Balch, R. E., W. E. Reeks & S. G. Smith. 1941. Separation of the spruce sawfly from Gilpinia polytoma (Hts.) (Diprionidae: Hymenoptera) and evidence of its introduction. Canad. Ent. 73: 198-203.
Bird, F. T. & J. M. Burk. 1961. Artificially disseminated virus as a factor controlling the European spruce sawfly, Diprion herycinae (Htg.), in the absence of introduced parasites. Canad. Ent. 92: 228-38.
Bird, F. T. & D. E. Elgee. 1957. A virus disease and introduced parasites as factors controlling the European spruce sawfly, Diprion hercyinae (Htg.) in central New Brunswick. Canad. Ent. 89: 371-78.
Briand, L. J. 1949. Notes on the spruce sawfly (Gilpinia hercyniae Htg.) and parasitism in the Park Reserve, Quebec, area. Quebec Soc. Protect. Plants Ann., 30th Rept. (1945-47): 180-81.
Cushman, R. A. 1940. A review of the parasitic wasps of the ichneumonid genus Exenterus Hartig. U. S. Dept. Agric. Misc. Publ. 354. 14 p.
Dahlsten, D. L. & N. J. Mills. 1999. Biological Control of Forest Insects. In: Bellows, T. S. & T. W. Fisher (eds.), Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p.
Daviault, L. 1944. Nouvelles observations sur la mouche a scie europeene de l'epinette dans les forets du nord du St-Laurent. Quebec Soc. Protect. Plants Ann. Rept. (1936-43): 39-43.
Dirks, C. O. 1944. Population studies of the European spruce sawfly in Maine as affected by natural enemies. J. Econ. Ent. 37: 238-42.
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McLeod, J. H. & G. Desalliers. 1966. Notes on Exenterus amictorius Panzer, an introduced parasite not established on the Swaine jack-pine sawfly, Neodiprion swainei Midd. Canad. Dept. Forest., Bimo. Prog. Rept. 22: 1-4.
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