Mesoleius tenthredinis 1 and Other Parasites of the Larch Sawfly in the Eastern United States

Abstract

The ability of the larch sawfly, Pristiphora erichsonii (Hartig), to resist an introduced hymenopterous parasite, Mesoleius tenthredinis Morley, by encapsulating its eggs was noted in the 1950's in central Canada and the Great Lake states. Examination of host prepupae from several eastern states indicated that populations of immune larch sawflies built up in this region in the early 1960's. The pteromalid Tritneptis klugii (Ratzeburg) and the tachinid Bessa harveyi (Townsend) were also found parasitizing the sawfly in portions of this region. B. harveyi is reported for the first time from New York and tentatively for the first time in Illinois. Eclytus n. sp. was identified from the larch sawfly in New York. Because the larch sawfly has a prolonged emergence period, it can only be economically controlled in forests and plantations through biological methods rather than insecticides. In view of the widespread distribution of sawfly strains resistant to M. tenthredinis in the eastern states, the release there of the European ichneumon Olesicampe benefactor Hinz, which was successfully introduced into Canada recently as a sawfly parasite, is recommended.