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LARCH SAWFLY, Pristiphora erichsonii (Hartig) -- Tenthredinidae

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A comparatively rare insect in Europe, the larch sawfly was first generally recognized as established in larch forests throughout the eastern Provinces of Canada in 1884. Several short lived but severe infestations were observed in 1906-16 in which hugh quantities of tamarack (Larix laricina) were destroyed (McGugan & Coppel 1962). Ever since the sawfly has been found throughout the range of larch in North America but remains more important on tamarack than on western larches. It is unknown whether the sawfly was a recent introduction in the late 19th Century or of much older origin in North America (Ives 1976). But the lack of native parasitoids prompted a classical biological control program in 1910-13, 1934 and 1961-64 (Dahlsten & Mills 1999).

Collections were made in Great Britain during the early phase of introductions (McGugan & Coppel 1962). They were shipped to Canada for quarantine, screening and direct release. This led to the establishment of the specific ichneumonid larval parasitoid Mesoleius tenthredinis Morley, which in Manitoba was found in 20% of sawfly cocoons in 1960 and had parasitized over 80% of the population by 1927 (Criddle 1928). Subsequently a tachinid Zenillia nox (Hall), was collected in Japan in 1934 by the U. S. Dept. of Agriculture and released both in New Brunswick and British Columbia but failed to establish. The success of parasitism by M. tenthredinis prompted an extensive relocation program to distribute this parasitoid throughout Canadian larch forests. Rapid establishment was reported with subsequent reductions in sawfly populations and reduced timber losses.

This appeared to be another example of the success of classical biological control in Canada, but in the late 1930's larch sawfly defoliation again became prevalent in Manitoba. Parasitism by M. tenthredinis appeared to have dropped to low levels, so 75,000 parasitoids were transferred from British Columbia across central Canada. While the parasitoids' range increased, levels of parasitism remained low due to the encapsulation of parasitoid eggs by host larvae (Muldrew 1953). The appearance of a resistant European strain of the sawfly, capable of encapsulating M. tenthredinis eggs, appears to have resulted from the parasitoid introduction program in 1913, when imported larch sawfly cocoons were placed directly in the field. The resistant strain has since spread across Canada and into neighboring states of the United States, becoming predominant in most regions (Wong 1974).

Renewed efforts were made in 1957 to obtain more parasitoids from Europe and Japan, and long term study plots were chosen in Manitoba to better evaluate the dynamics of the larch sawfly populations and the impact of introductions. These studies (Ives 1976) indicated that mortality in the cocoon and adult stages determined population trends and that high water tables and predation by small mammals were largely responsible for the erratic population abundance. The native tachinid, Bessa harveyi (Tns.), considered the most important parasitoid in the renewed outbreaks, had little impact.

The Commonwealth Institute of Biological Control collected 11 parasitoids in Europe and Japan and shipped them to Canada between 1959-65. Five of the more abundant species were selected for release and >200 adult were liberated. A separate introduction of the masked shrew, Sorex cinereus Kerr from New Brunswick to the island of Newfoundland was made in 1958 in order to fill the vacant niche for an insectivore and to increase cocoon predation. The shrew as successfully established as well as two of the parasitoids. One of these parasitoids, the ichneumonid Olesicampe benefactor Hinz., attacks young sawfly larvae, the second, a Bavarian strain of M. tenthredinis, was shown to be only weakly encapsulated by the resistant sawfly strain and was able to pass its characteristics on to the progeny of mixed (Britain X Bavarian) crosses (Turnock & Muldrew 1971). Parasitism by M. tenthredinis initially increased following the release of the Bavarian strain but O. benefactor became the dominant parasitoid influencing cocoon survival. Parasitism by the latter at the release point in Manitoba attained levels of ca. 90% between 1967-72 (Ives 1976) and was the dominant factor for the collapse of the sawfly epizootic (ives 1976). Olesicampe benefactor was relocated from Manitoba to most other Provinces in Canada (Turnock & Muldrew 1971) as well as to Maine (Embree & Underwood 1972), Minnesota (Kulman et al. 1974) and Pennsylvania (Drooz et al. 1985).

Effects of the masked shrew on larch sawfly cocoon survival in Newfoundland has never been adequately estimated. Predation of cocoons is thought to have increased (Dahlsten & Mills 1999), but outbreaks have continued through the 1970's (Ives 1976). Therefore, O. benefactor seems to offer the greatest potential for controlling larch sawfly in Canada. However in 1966 a hyperparasitoid, Mesochorus globulator Thunb. began to attack this parasitoid in Manitoba. The polyphagous hyperparasitoid is common in Europe and may also have been accidentally introduced during the initial 1910-13 introductions (Dahlsten & Mills 1999). It has spread throughout the region and into Wisconsin, although it hasn't been reported from Pennsylvania (Drooz et al. 1985). While hyperparasitism attained very high levels (80-90%) in Manitoba during 1970's, sawfly populations continue to remain low in abundance, and thus control may be achieved by O. benefactor despite the occurrence of the hyperparasitoid.

The larch sawfly program gives further evidence of the value of the more specific and well adapted parasitoids in classical biological control. As in the case of the European spruce sawfly, while a wide range of parasitoids was released, only the more specific species became established. However, while in the absence of hyperparasitism O. benefactor may have been an ideal control agent, its competitive superiority over the Bavarian strain of M. tenthredinis may have prevented the latter from establishing and spreading more widely (Dahlsten & Mills 1999). This and the known occurrence of various geographic strains of M. tenthredinis differing in ability to avoid encapsulation by the host, emphasizes the value of detailed studies of parasitoid biologies prior to introduction. Also, the accidental introduction of both a parasitoid resistant strain of the host and probably also a hyperparasitoid indicates the critical need for quarantine handling of imported material to avoid unnecessary liberations.

For further detail on biological control effort, and biologies of host and natural enemies, please see the following (Hewitt 1912, Graham 1931, 1953; Hopping et al. 1943, Hawboldt 1947, McLeod 1952, 1954; Lejuene & Hildahl 1954, Reeks 1954, Muldrew 1955, 1967; Drooz 1957, 1960, 1961; Ives & Prentiss 1959, Turnbull & Chant 1961, Turnock 1960, Dowden 1962, Pschorn-Walcher & Eichhorn 1963, Eichhorn 1965, Eichhorn et al. 1965).

REFERENCES: [Additional references may be found at: MELVYL Library ]

Bellows, T. S. & T. W. Fisher (eds.). 1999. Handbook of Biological Control: Principles and Applications. Academic Press, San Diego, New York. 1046 p.

Criddle, N. 1928. The introduction and establishment of the larch sawfly parasite, Mesoleius tenthredinus Morley, into southern Manitoba. Canad. Ent. 60: 51-53.

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

Dowden, P. B. 1962. Parasites and predators of forest insects liberated in the United States through 1960. U. S. Dept. Agric. Agric. Handbk. 226: 70 p.

Drooz, A. T. 1957. The importance of Mesoleius tenthredinis Morl., a parasite of the larch sawfly, in New York State. J. Econ. Ent. 50: 212.

Drooz, A. T. 1960. The larch sawfly, its biology and control. U. S. Dept. Agric. Tech. Bull. 1212. 52 p.

Drooz, A. T. 1961. Mesoleius tenthredinis Morl. in Pennsylvania and Michigan. Canad. Ent. 93: 804-07.

Drooz, A. T., J. W. Quimby, L. C. Thompson & H. M. Kulman. 1985. Introduction and establishment of Olesicampe benefactor Hinz (Hymenoptera: Ichneumonidae), a parasite of the larch sawfly, Pristiphora erichsonii (Hartig) (Hymenoptera: Tenthredinidae), in Pennsylvania. Environ. Ent. 14: 420-23.

Eichhorn, O. 1965. Uber einige Lärchenschädlinge und ihre Parasiten in Japan, Europa und Kanada. Betr. Ent. 15: 111-26.

Eichhorn, O., H. Pschorn-Walcher & D. Schröder. 1965. Neue Untersuchungen sur biologischen Bekámpfung verschleppter Forstinsekten. 2. Bericht über die Arbeiten der europäischen Station des Commonwealth Institute of Biological Control, Delémont, Switzerland. Pt. II. Anz. Schädlingsk. 38: 104-09.

Embree, D. G. & G. R. Underwood. 1972. Establishment in Maine, Nova Scotia and New Brunswick of Olesicampe benefactor (Hymenoptera: Ichneumonidae), an introduced ichneumonid parasite of the larch sawfly, Pristiphora erichsonii (Hymenoptera: Tenthredinidae). Canad. Ent. 104: 89-96.

Graham, A. R. 1931. The present status of the larch sawfly, (Lygaeonamatus erichsonii Hartig), in Canada, with special reference to its specific parasite, Mesoleius tenthredinis

Graham, A. R. 1953. Biology and establishment in Canada of Mesoleius tenthredinis Morley (Hymenoptera: Ichneumonidae), a parasite of the larch sawfly, Pristiphora erichsonii (Hartig) (Hymenoptera: Tenthredinidae). Quebec Soc. Protect. Plants, 35th Ann. Rept.: 61-75.

Hawboldt, L. S. 1947. Bessa selecta (Meigen) (Diptera: Tachinidae) as a parasite of Gilpinia hercyniae (Hartig). Canad. Ent. 79: 84-104.

Hewitt, C. G. 1912. The larch sawfly (Nematus erichsonii) with an account of its parasites, other natural enemies and means of control. Canad. Dept. Agric. Bull. 10 (2nd Ser.), Ent. Bull. 5: 7-42.

Hopping, G. R., H. B. Leech & C. V. G. Morgan. 1943. The larch sawfly, Pristiphora erichsonii (Hartig), in British Columbia with special reference to the cocoon parasites Mesoleius tenthredinis Morley and Tritneptis klugii (Ratzburg). Sci. Agr. (Ottawa) 24: 53-63.

Ives, W. G. H. 1976. The dynamics of larch sawfly (Hymenoptera: Tenthredinidae) populations in southeastern Manitoba. Canad. Ent. 108: 701-30.

Ives, W. G. H. & R. M. Prentice. 1959. Estimation of parasitism of larch sawfly cocoons by Bessa harveyi Tnsd. in survey collections. Canad. Ent. 91: 496-500.

Kulman, H. M., L. C. Thompson & J. A. Witter. 1974. Introduction of parasitoids of the larch sawfly in Minnesota. Great Lakes Ent. 7: 23-25.

Lejeune, R. R. & V. Hildahl. 1954. A survey of the parasites of the larch sawfly (Pristiphora erichsonii (Hartig)) in Manitoba and Saskatchewan. CAnad. Ent. 86: 337-45.

McGugan, B. M. & H. C. Coppel. 1962. A review of the biological control attempts against insects and weeds in Canada. II. Biological control of forest insects, 1910-1958. Commonwealth Inst. Biol. Control Tech. Comm. No. 2: 35-216.

McLeod, J. H. 1952. Notes on the population and parasitism of the larch sawfly Pristiphora erichsonii (Htg.) (Hymenoptera: Tenthredinidae) in British Columbia. Ent. Soc. Brit. Columbia Proc. (1951) 48: 81-5.

Muldrew, J. A. 1953. The natural immunity of the larch sawfly (Pristiphora erichsonii (Htg.)) to the introduced parasite (Mesoleius tenthredinis Morley), in Manitoba and Saskatchewan. Canad. J. Zool. 31: 313-32.

Muldrew, J. A. 1955. Parasites and insect predators of the larch sawfly. Canad. Ent. 87: 117-20.

Muldrew, J. A. 1967. Biology and initial dispersal of Olesicampe (Holocremnus) sp. nr. nematorium (Hymenoptera: Ichneumonidae), a parasite of the larch sawfly recently established in Manitoba. Canad. Ent. 99: 312-21.

Pschorn-Walcher, H. & O. Eichhorn. 1963. Investigations on the ecology and natural control of the larch sawfly (Pristiphora erichsonii (Htg.) Hym., Tenthredinidae) in Central Europe. Part I. Abundance, life-history and ecology of P. erichsonii and other sawflies on Larch. Commonwealth Inst. Biol. Control, Tech. Bull. 3: 51-81.

Reeks, W. A. 1954. An outbreak of the larch sawfly (Pristiphora erichsonii (Htg.)) in the Maritime Provinces (Hymenoptera: Tenthredinidae) and the role of parasites in its control. Canad. Ent. 86: 471-80.

Turnbull, A. L. & D. A. Chant. 1961. The practice and theory of biological control of insects in Canada. Canad. J. Zool. 39: 697-753.

Turnock, W. J. 1960. Ecological life-history of the larch sawfly, Pristiphora erichsonii (Htg.) (Hymenoptera: Tenthredinidae), in Manitoba and Saskatchewan. Canad. Ent. 92: 500-16.

Turnock, W. J. & J. A. Muldrew. 1971. Chapter 45. Pristiphora erichsonii (Hartig), larch sawfly (Hymenoptera: Tenthredinidae), p. 175-94. In: Biological Control Programmes Against Insects and Weeds in Canada. 1959-1968. Commonwealth Inst. of Biol. Control, Tech. Commun. No. 4. 266 p.

Wong, H. R. 1974. The identification and origin of the larch sawfly, Pristiphora erichsonii (Hymenoptera: Tenthredinidae) in North America. Canad. Ent. 106: 1121-31