THE IDENTIFICATION AND ORIGIN OF THE STRAINS OF THE LARCH SAWFLY, PRISTIPHORA ERICHSONII (HYMENOPTERA: TENTHREDINIDAE), IN NORTH AMERICA

Abstract

This study identifies and presents a key to five strains of the larch sawfly, Pristiphora erichsonii (Hartig), which are designated Aweme, Fernie, Ambleside, Thirlmire, and Salzburg.Aweme and Fernie strains occur only in North America and Salzburg strain is confined to Eurasia. Two Eurasian strains, Ambleside and Thirlmire, were accidentally introduced into Canada from England by 1913 among cocoons shipped for the release of the parasite Mesoleius tenthredinis Morley. It is postulated that the ancestors of Aweme-Salzburg strains Fernie–Thirlmire strains dispersed across the Bering Land Bridge into North America some time in the Miocene. These phyletic lines evolved into distinct Eurasian and North American strains. Early infestations in North America apparently consisted of North American strains, while later outbreaks have consisted primarily of the recently introduced Eurasian strains.