Effects of Exposure to Pesticides on Carbaryl Toxicity and Cytochrome P450 Activities in Aedes albopictus Larvae (Diptera: Culicidae)

Cytochrome P450 monooxygenase (P450)-mediated metabolism is an important mechanism by which insects detoxify insecticides. In this report, a major contribution of P450s as a mechanism of insecticide detoxification was demonstrated by the effect of herbicides and fungicides and the synergist piperonyl butoxide on carbaryl toxicity and P450 activities in the mosquito Aedes albopictus. Mosquito larvae preexposed to technical and analytical grade pentachlorophenol (PCPT, PCPA) showed significant increases of survival from carbaryl toxicity. This phenomenon was reversed when piperonyl butoxide was also applied. Microsomes from PCPT- and PCPA-treated larvae showed higher levels of N-demethylation of p-chloro-Nmethylaniline than those from control larvae. Microsomes from larvae treated with PCPT also yielded a very high level of Odemethylation of methoxyresorufin. However, peroxidation of tetramethylbenzidine was decreased in both treated groups. This suggests that PCP may induce certain P450 isozymes but suppress others. SDS-PAGE bands corresponding to the molecular weights of 61 and 63 kDa presented strong intensity in the treated microsomes; these may represent P450s induced by PCP. P450s in the mosquito larvae are active, inducible, and capable of detoxifying the insecticide carbaryl.