The effect of host plant on the effectiveness of Thuricide, a commercial formulation of Bacillus thuringiensis sp. kurstaki Berliner, toward gypsy moths, Lymantria dispar L., was examined. Thuricide was administered to second- and fourth-instar gypsy moths on foliage from red oak, Quercus rubra L.; chestnut oak, Quercus prinus L.; and quaking aspen, Populus tremuloides Michaux. Oaks were 2-5 times more inhibitory of Thuricide than aspen. Red oak was more inhibitory than chestnut oak. The differences among host-plant species were greatest at the higher dose of 34 IU per larva. Mortality was correlated negatively with the concentration of total phenolics, gallotannins, and proteinbinding activity in leaves. Purified tannins from the oaks were highly inhibitory, indicating that leaf tannins are primarily responsible for reducing the effectiveness of Thuricide. We conclude that oak tannins reduce the effectiveness of this B. thuringiensis formulation, that stand composition may have a major effect on the effectiveness of microbial control measures, and that tannin inhibition may represent a useful target for formulation improvement.
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Appel et al. (1994) studied this question.