FIELD ASSESSMENT OF BACILLUS-THURINGIENSIS ON NONTARGET LEPIDOPTERA

Nontarget effects of a single aerial application of Bacillus thuringie nsis at 90 BIU/ha were studied on native Lepidoptera in west central V irginia in 1992 (treatment year) and in 1993 and 1994 (recovery years) . Overall caterpillar abundance was lower on foliage collections from sprayed plots, but differences were modest and mostly not significantl y. Nineteen of 20 common species from foliage decreased in relative ab undance following the application of B. thuringiensis, although we cou ld not demonstrate a significant treatment effect for any 1 of the 19. Greatest impacts were seen in the macrolepidopteran fauna beneath bur lap bands. Eleven of the 12 more frequently encountered species were s ignificantly less common on the treatment plots in 1992. Taken collect ively, 4 of our species [Phoberia atomaris Hubner and Orthosia rubesce ns (Walker) both Noctuidae), Malacosoma disstria Hubner (Lasiocampidae ), adn Satyrium calanus (Hubner) (Lycaenidae)] were recovered 10 times more often from out control plots following the application of B. thu ringiensis. Caterpillar numbers rebounded in the 1st post-spray year ( 1993), with only M. disstria and P. atomaris remaining significantly l ess common on treatments plots; reduced abundance on the latter contin ued through our 2nd post-year samples.