Influence of alternative host plant feeding on aldrin susceptibility and detoxification enzymes in western and northern corn rootworms

Pioneer populations of western corn rootworm in central Pennsylvania, depending on their food, are 90 to 1200 times more resistant to aldrin than an endemic population of northern corn rootworm. Susceptibility of western corn rootworm to aldrin was markedly increased up to nine times when adults were maintained on diets other than corn, whereas the northern species was equally susceptible to aldrin on all diets. Adult western and northern corn rootworms exhibited differential host plant induction of three detoxification enzymes potentially involved in aldrin metabolism. Activities of microsomal aldrin epoxidase and to a lesser extent cytosolic glutathione transferase in midgut tissues of both species were increased up to three times by diet shifts from corn ear to squash blossom and sunflower inflorescence. In addition, microsomal cis- and trans-epoxide hydrolase in northern corn rootworm were significantly induced, while levels of these enzymes in the western species were unaffected by diet. Northern corn rootworm exhibited higher levels of induction for all enzymes. The induction of the epoxidase without a concomitant increase in epoxide hydrolase can account for the diet-dependent increase in susceptibility observed for western corn rootworm, since the epoxidation reaction, in contrast to epoxide hydration, results in a product that is equal to or more toxic than aldrin itself. The more frequent consumption of alternative foods by the northern over the more corn-specializing western species could over many generations markedly alter aldrin resistance mechanisms in absence of insecticide selection, and thereby increase aldrin susceptibility in formerly resistant populations.