Do Detoxification Enzymes Enable Generalism By Japanese Beetles?

Detoxification enzymes are an adaptation of insect herbivores to breakdown toxic compounds present in their food. However, little is known about the activities of these enzymes in Japanese beetle, a generalist herbivore and their role in mediating host plant utilization by this insect. The induction of detoxification enzymes, cytochrome P450, glutathione S transferase (GST) and carboxylesterase (CoE) in the midgut of adult Japanese beetles, was compared between cohorts of beetles fed preferred or non-preferred host plants, and insects fed a mixture of host plants (polyphagy) or a single plant (monophagy). The activities of P450, GST and CoE in the midgut of Japanese beetles fed with host plants after feeding were assayed and compared to starved beetles. Japanese beetles consumed significantly more mass of preferred hosts relative to non-preferred hosts. Non-preferred hosts, generally induced higher activities of P450, GST and CoE. Similarly, beetles fed mixed diets had generally greater enzyme activities. Elevated activities of detoxification enzymes likely explain the reported differences in host preference. Japanese beetles induce metabolically expensive enzymes when consuming marginal hosts or when switching hosts. The fitness costs associated with these enzymes may explain the reduced longevity or fecundity noted for non-preferred hosts in single and mixed diets.