GENETIC-BASIS FOR DIFFERENT HOST USE IN EPILACHNA-PUSTULOSA, A HERBIVOROUS LADYBIRD BEETLE

The genetic basis for different host plant use was studied in a herbiv orous ladybird beetle, Epilachna pustulosa, that exhibits interpopulat ional variation in host plant utilization. It usually depends on thist le, but one of the local forms occurs on both thistle and blue cohosh, which differ at the infraclass taxonomic level. In this local populat ion, genetic association between the developmental performance on the two plants was neutral, suggesting genetic independence across the hos t plants. The form of reaction norms indicated some changes in relativ e rank position. Genetic variation among individuals on each host plan t was detected. These results suggest that different genotypes are sel ected on different host plants and that a substantial proportion of th e overall phenotypic plasticity is contributed by genotype-dependent e nvironmental effects.