The Insect Parasites of the Spruce Sawfly (Diprion polytomum, Htg.) in Europe

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Abstract
A severe outbreak of the Spruce Sawfly (Diprion polytomum, Htg.) in Eastern Canada led to a request to Farnham House Laboratory to investigate, and if possible collect and export, the parasites of this insect in its native home in Europe.Work started in 1932 and it was found thatD. polytomumwas a comparatively rare insect in Europe, though widely distributed. It is heavily parasitized, 31 species of Hymenopterous and Dipterous parasites having been found up to the present. Nearly twenty-eight million parasitized cocoons and eggs of this and other species ofDiprionhave been collected and despatched from Europe, and work is still continuing.Previous to the present work only 13 species of parasites, a list of which is given, were recorded from this host.Of the 31 species now known, 15 are primary, 5 can be primary or secondary, and 9 secondary only; in 2 cases the status is not known.Descriptions of all the species are given and in the case of the obligatory and facultative primaries, the biology and immature stages are also described and notes added on their suitability for introduction into Canada. A key to the adult parasites is given, and a key to the larval stages of the primary and facultative primary parasites. Some practical notes are also given, including methods of accelerating the emergence of parasites in winter and methods of preparing parasite larvae for examination and identification.