Effects of plant diet on detoxification enzyme activities of two grasshoppers, Melanoplus differentialis AND Taeniopoda eques

The polyphagous grasshoppers Melanoplus differentialis and Taeniopoda eques use different foraging patterns: over time M. differentialis tends to redu ce the variety of host plants it feeds on and specialize on particular plan ts (diet components), whereas T. eques mixes host plants to achieve a very diverse diet. We tested the hypothesis that these differing behaviors are c orrelated with differing patterns of detoxification enzymes. The activities of midgut, fat body, and malpighian tubule detoxification enzymes were det ermined in last instars of the two grasshoppers, reared for five days on si ngle- or mixed-plant diets. Significant differences in several cytochrome P 450 activities and glutathione S-transferase were evident for nymphal grass hoppers feeding on different plant diets. However, the behavioral differenc es between the two species could not be explained by an underlying flexibil ity of detoxification response in M. differentialis, but lacking in T. eque s. This is the first reported evidence that detoxification enzyme activitie s are affected by plant diet in polyphagous orthopterans.