Despite the fact that the potential exists for selection to increase the frequency of resistance traits in both plant and insect populations, a substantial amount of genetic variation exists for such traits. Such variation suggests that there may be selective tradeoffs associated with the evolution of resistance. One such tradeoff is the cost of resistance--that is, the reduced fitness of resistant genotypes in the Depressaria pastinacella (parsnip webworm) and its host wild parsnip (Pastinaca sativa). In this system, phytochemical resistance factors in the plant are known to exhibit genetic variation, as are detoxicative qualitative data for refining theoretical expectations of plant-insect coevolution as well as for designing and implementing resistance management programs in agroecosystems.
