ESTABLISHMENT, DISTRIBUTION, AND IMPACT IN SOUTHERN NEW ENGLAND OF LATHROLESTES NIGRICOLLIS (THOMPSON) (HYMENOPTERA: ICHNEUMONIDAE), AN INTRODUCED PARASITOID OF THE BIRCH LEAFMINER, FENUSA PUSILLA (LEPELETIER) (HYMENOPTERA: TENTHREDINIDAE)

Lathrolestes nigricollis (Thompson) (Hymenoptera: Ichneumonidae) was released in New England against Fenusa pusilla (Lepeletier) in 1979–1980 and again in 1989–1990. By 1991, the parasitoid was widely established in southern New England. From 1979 to 1990 the commonness of leafminers at the original release site in the first generation declined from 50–54% of leaves mined to under 3%. Over 4 years at five sites, parasitism of larval birch leafminers increased between leafminer generations from 10.3% (G1) to 27.6% (G2) to 39.2% (G3). In Massachusetts, parasitism decreased (from 28 to 14%) with increasing distance from the original release site, while corresponding damage increased (from 6% of leaves mined to 33%). In areas local to the original release site (<4 km) parasitism has reduced damage from birch leafminer to inconsequential levels. Some sites in other parts of southern New England, particularly roadside sites, still have high levels of mined leaves in spite of the parasitoid’s presence in the general area.