Ontogeny, sex and adult tissues influence activities of detoxification enzymes in the Japanese beetle (Popillia japonica Newman)

Abstract

The detoxification enzymes superfamilies of cytochrome P450 (P450), glutathione S‐transferase (GST) and carboxylesterase (CoE) play important roles in the metabolism of xenobiotics and endogenous substrates. Despite their importance in insect physiology and ecology, the relative activities of these enzyme systems among developmental stages, sexes and tissues of insect species have not been studied extensively. In the present study, we determine the relative activities of these enzymes in eggs, larval stages, adults of each sex and different tissues of the Japanese beetle (Popillia japonica Newman) in response to model exogenous substrates. The effect of food deprivation on enzyme activities is also examined in adult gut tissue. In this scarab species, ontogeny influences enzyme activities and catalytic efficiency, with eggs exhibiting only GST activity, first‐instar larvae exhibiting GST and CoE activities, and other life stages exhibiting P450 7‐ethoxycoumarin O‐deethylation (ECOD), GST and CoE activities. Second‐instar larvae have the highest GST activity, whereas third‐instar larvae have the highest P450 and CoE activities. Male and female adults show differences in P450 ECOD activity but not in CoE activity. Adult tissues vary in enzyme activities, with midgut tissues having the greatest P450 ECOD and CoE activities. A feeding bout of 24 h induces the optimal activities of P450 ECOD, GST and CoE in the gut of adult beetles. Interestingly, activity of GST is induced upon prolonged starvation. The findings of the present study highlight the apparent importance and contribution of detoxification enzymes in the physiology and ecology of this economically‐important pest.