EFFECTS OF BACILLUS THURINGIENSIS BERLINER VAR. KURSTAKI AND DEFOLIATION BY THE GYPSY MOTH [LYMANTRIA DISPAR (L.) (LEPIDOPTERA: LYMANTRIIDAE)] ON NATIVE ARTHROPODS IN WEST VIRGINIA

Impacts of Bacillus thuringiensis var. kurstaki (Btk) and defoliation by gypsy moth [Lymantria dispar (L.)] on native, non-target arthropods were evaluated in eastern West Virginia from 1990 to 1992. Adult and larval arthropods were collected by foliage sampling and light-trapping at 24 20-ha (50-acre) plots, representing six replicates of four treatments: unsprayed, gypsy moth absent (control); unsprayed, gypsy moth present (defoliation); sprayed, gypsy moth absent; and sprayed, gypsy moth present. Pre-treatment data were collected in 1990. In May 1991, one application of Btk was made to 12 plots at a dosage of 14.4 BIU/ha (36 BIU/acre). Post-treatment data were collected in 1991 and 1992. With few exceptions, detectable effects from Btk application were restricted to Lepidoptera. Although abundance and species richness of larval and adult non-target Lepidoptera decreased at all plots between 1990 and 1992, abundance and species richness were reduced at Btk-treated plots relative to untreated plots. Richness and abundance of some larval and adult Lepidoptera declined at defoliation plots. Although the short-term (< 1 year) impacts of Btk application on non-target Lepidoptera are negative, the long-term effects (> 1 year) of reduced abundance of gypsy moth larvae may be beneficial for some native species. Although Btk application and defoliation reduce abundance of native Lepidoptera, environmental conditions such as weather may have a greater influence on population fluctuations.