Field Assessment of Bacillus thuringiensis on Nontarget Lepidoptera

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Abstract
Nontarget effects of a single aerial application of Bacillus thuringiensis at 90 BIU/ha were studied on native Lepidoptera in west central Virginia 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 significant. Nineteen of 20 common species from foliage decreased in relative abundance following the application of B. thuringiensis, although we could not demonstrate a significant treatment effect for any 1 of the 19. Greatest impacts were seen in the macrolepidopteran fauna beneath burlap bands. Eleven of the 12 more frequently encountered species were significantly less common on the treatment plots in 1992. Taken collectively,4 of our species [Phoberia atomaris Hiibner and Orthosia rubescens (Walker) (both Noctuidae), Malacosoma disstria Hübner(Lasiocampidae), and Satyrium calanus (Hübner) (Lycaenidae)] were recovered 10 times more often from our control plots following the application of B. thuringiensis. Caterpillar numbers rebounded in the 1st post-spray year (1993), with only M. disstria and P. atomaris remaining significantly less common on treatment plots; reduced abundance of the latter continued through our 2nd post-year samples.

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