Role in insecticidal resistance

Progress has also been made in molecular studies of cytochrome P-450 monooxygenases that are known to play an important role in insecticide resistance. The cytochrome P-450 gene from the house fly has been cloned, which should enable studies of the genetic regulation of insect cytochrome P-450 and further elucidation of its role in insecticide resistance (fil)-... 

Glutathione S-transferases have received considerable attention because of their roles in insecticide detoxification and resistance in insects. Cytosolic glutathione S-transferases have been purified from more than two dozen insect species, including Lepidoptera, Diptera, Coleoptera, Dictyoptera, and Hymenoptera. These transferases exist in multiple forms as many as nine isozymes were found in midguts and fat bodies of fall army worm... 

David JP, Ismail HM, Chandor-Proust A, Paine MJI (2013) Role of cytochrome P450s in insecticide resistance impact on the control of mosquito-borne diseases and use of insecticides on Earth. Philos Trans Royal Soc B-Biol Sci 368 20120429... 

Further, by virtue of their larger livers, the R fish have a greater xenobiotic biotransformation potential. However, the in vivo studies show few consistent differences in metabolism between the two populations. Biotransformation may be a major contributory factor in mosquitofish resistance to other pesticides, for example, organophosphorus and botanical insecticides, since the level of resistance to these chemicals is very low (4 fold or less) 08,20,21). However, biotransformation does not appear to play a major role in organochlorine insecticide resistance. 

GSTs also play an important role in resistance to chemical toxicity. GSTs have been implicated in resistance to the effects of a variety of chemicals including antibiotics, anticancer agents, analgesics, herbicides, insecticides, and vasodilators. Preneoplastic lesions, tumors, and cultured tumor cell lines commonly overexpress GSTs of the classes alpha, mu, and pi. This overexpression of GSTs is considered partly responsible for the resistance often associated with these cells to cancer chemotherapeutics. 

Detoxification enzymes such as cytochrome P450 monooxygenases, glutathione S-transferases, and hydrolases play important roles in the metabolism of and resistance to insecticides in insects. These enzymes possess the capacity for rapid increases in activity in response to chemical stress, a phenomenon known as enzyme induction. Readers are referred to reviews by Terriere and Yu (1974), Terriere (1984), Brattsten (1979), Yu (1986a, 1996, 2001) and Feyereisen (2005) for discussion of work pertaining to induction of detoxification enzymes in insects. 

Devonshire, A.L., The properties of a carboxylesterase from the peach-potato aphid, Myzuz persicae (Sulz.), and its role in conferring insecticide resistance, Biochem. J., 161, 675,1977. 

Despite the hick of use of PBO on food and fibre crops, evidence is accumulating for effects me dialed by PBO alone, that may have a significant role in the control of insects, particularly ones that have developed resistance to conventional insecticides. This chapter reviews such effects and summarizes research into the potential use of PBO in controlling the cotton whitefly, llemisiti rabaci. Results of this work will be published formally in due course. 

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. 

Over the past 30 years, insecticides based on naturally occurring isolates of Bt have played, and will continue to play, an increasingly important role in addressing specific pest management problems such as insecticide resistance and environmental pollution. However, there are several characteristics of Bt which currently limit its widespread adoption in agriculture. These include ... 

Although implicated less frequently in arthropod pesticide resistance, diminished sensitivity of target sites in the nervous system is a major factor in many cases of resistance to different classes of insecticides. As more is learned about this phenomenon, we may find that it plays a more important role in resistance than is currently known. There are two major types of target site insensitivity. Uith insecticides such as DDT, certain other... 

Extensive research has shown that points 7 and 8 are almost always involved, but with the other factors playing a modifying or additional role. Enhanced detoxication of the insecticide is often found in the resistant insect,... 

---