ASPEN LEAF QUALITY AFFECTS GYPSY-MOTH (LEPIDOPTERA, LYMANTRIIDAE) SUSCEPTIBILITY TO BACILLUS-THURINGIENSIS

We assessed variation in Bacillus thuringiensis subsp. kurstaki toxici ty against gypsy moth, Lymantria dispar (L.), larvae reared on differe nt aspen trees, and how such variation may be linked to foliar chemist ry, particularly phenolic glycosides. Larvae were reared on foliage fr om five different trees. LD(50)s were determined using third instars a nd six doses of B. thuringiensis (Foray 48B). Results skewed 100-fold variation in B. thuringiensis toxicity for larvae reared on different trees. Chemical analyses of leaf material suggested that condensed tan nins and perhaps phenolic glycosides affect B. thuringiensis toxicity. Feeding studies with artificial diets containing various levels of B. thuringiensis and phenolic glycosides confirmed that the secondary co mpounds can strongly enhance the efficacy of B. thuringiensis.