Resistance mechanisms to carbamate and organophosphate insecticides.
Organophosphates (OPs), introduced in 1944, and carbamates, introduced in 1956, remain widely used and effective insecticides although not free from resistance problems. Metabolic resistance to Ops was reported 14 years after their introduction, compared to only 7 years for DDT and 5 for the carbamates. The complex metabolic fate of the Ops, including attack by cytochrome P-450 leading either to activation or detoxification, as well as by glutathione transferases and esterases, may play a role in this delay. Carbamates are not bioactivated; they are detoxified by cytochrome P-450. In the presence of a continued selection pressure, metabolic resistance may facilitate the evolution of other defenses such as target site resistance, reported for the OPs and carbamates 6 and 10 years after metabolic resistance. Target site resistance to OPs and carbamates resides in modified forms of acetyl-cholinesterases (AChEs) with reduced affinity for the insecticides. AChE-based target site resistance does not necessarily confer cross resistance to all other OPs and carbamates and may be unstable in the absence of a selection pressure.Show more [+] Less [-]