INSECT BIOCHEMICAL DEFENSES AGAINST TOXIC COMPOUNDS

Chemical control has so far successfully controlled mosquitoes in NJ. However, continued use of any insecticide increases the risk of resistance evolution in stressed populations. It is, thus, very important to monitor populations for potential resistance development. Developing molecular probes for resistance is the aim of this project. Epidemic outbreaks of mosquito-transmitted diseases occur with some frequency worldwide because vector control fails due to insecticide resistance. There are many documented cases of insecticide resistance in mosquitoes including an Aedes aegypti population resistant to temephos, Ae. taeniorhynchus to methoprene, Culex pipiens to Bacillus sphaericus (BS), C. quinquefasciatus to Bti. AFlorida population of Ae. albopictus is resistant to malathion and B. sphaericus. In Texas and Kansas, Ae. albopictus is susceptible to malathion but in parts of Texas and Ohio, it is resistant. Temephos and malathion are old, effective organophosphate insecticides that are being phased out. Metabolic resistance to organophosphates can result from detoxification by cytochrome P450 and carboxylesterase activities; to pyrethroids, it can be caused by detoxification by cytochrome P450 and carboxylesterases. Resistance to Bti and BS depends on proteases and peptidases, hydrolytic enzymes related to carboxylesterases. Resistance to methoprene can be caused by detoxification by a cytochrome P450 and an esterase or both. Resistance to the carbamate insecticide carbaryl in insects depends on detoxification by cytochrome P450 only, which makes carbaryl toxicity a reliable indicator of cytochrome P450 activities. Carbaryl toxicity studies are included in this research as an indicator of cytochrome P450 activity although it is not used for mosquito control in NJ. Spinosad is also exclusively detoxified by cytochrome P450 in Ae. sollicitans. Although it is still possible to control salt marsh mosquitoes in New Jersey with the available insecticides, these mosquitoes possess a high potential for evolving resistance when the selection pressure increases because of a continually diminishing choice of compounds that can effectively be used in insecticide rotations. Increasingly, the NJ salt marsh mosquitoes are being treated exclusively with Bti. Our experiments so far show clearly that both cytochrome P450s and esterases are present and active in the mosquitoes.