Effects of genetic structure of Lupinus arboreus and previous herbivory on Platyprepia virginalis caterpillars

Two leaf-feeding caterpillars, western tussock moth (Orgyia vetusta) and ranchman's tiger moth (Platyprepia virginalis) are abundant on Lupinus arboreus along the California coast. Previous experiments and observations suggested that feeding caused by either of these two folivores could reduce the performance and possibly the abundance and distribution of the other species. Previous common garden experiments also indicated that genetically determined characteristics of the host plants were important for O. vetusta. Here we examined the effects of familial origin of the host plant, and previous damage caused by O. vetusta on the abundance of P. virginalis. Plants with parents from one of three locations had higher numbers of P. virginalis than plants with parents from the other two locations. However, this effect of plant origin depended on the statistical analysis and was not as strong as the effect of prior damage by O. vetusta on numbers of P. virginalis. Counter to our expectation. bushes that supported higher levels of damage by O. vetusta in the previous summer had more P. virginalis caterpillars. This strong effect could result by both moth species selecting bushes with the same traits or as the result of herbivory by O. vetusta enhancing the susceptibility of bushes for P. virginalis.