BACILLUS THURINGIENSIS δ-ENDOTOXEV: ON THE RELATIVE ROLES OF SPORES AND CRYSTALS IN TOXICITY TO SPRUCE BUDWORM (LEPIDOPTERA: TORTRICIDAE)

Abstract

AbstractNewly moulted sixth instar larvae of spruce budworm, Choristoneura fumiferana, were force fed graded dosages of preparations containing (1) purified crystals, (2) purified spores, and (3) mg/mg mixtures of purified spores and purified crystals. The LD50 for purified crystals was 0.094 μg/larva and for the mixture 0.096 μg/larva but the latter preparation had an LD50 of 0.048 μg/larva based on crystals indicating that the presence of 2.4 × 105 spores enhanced the toxicity of crystals twofold. The LD50 spore crystal corresponded to LD60 for crystals alone. The LD50 for spores treated with proteinase to remove residual crystals was 20 μg/larva, or 1,0 × 108 spores. The regression coefficients were not significantly different from each other in all three preparations indicating a common or similar mode of action. It is concluded that spores play little or no role in mortality of spruce budworm induced by Bacillus thuringiensis insecticides.