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

We assessed variation in Bacillus thuringiensis subsp. kurstaki toxicity against gypsy moth, Lymantria dispar (L.), larvae reared on different aspen trees, and how such variation may be linked to foliar chemistry, particularly phenolic glycosides. Larvae were reared on foliage from five different trees. LD(50)s were determined using third instars and 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 tannins 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 compounds can strongly enhance the efficacy of B. thuringiensis.