Organophosphorus insecticides resistance

Campbell, P.M., Newcomb, R.D., Russell, R.J., and Oakeshott, J.G., Two different amino acid substitutions in the ali-esterase, E3, confer alterative types of organophosphorus insecticide resistance in the sheep blowfly, Lucilia cuprina, Insect Biochem. Molec. Biol., 28,139,1998. 

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. 

Carboxylesterases are well-represented in insects and are sometimes important in the development of resistance to insecticides. Thus, a well-characterized carboxylesterase E4 is responsible for resistance to organophosphorus insecticides in the aphid (Myzuspersicae) [107]. In the California Culex mosquito, the esterase B1 is 500-fold more abundant in organophosphate-resistant than in susceptible insects. The increase of esterase levels is the result of gene amplification, i.e., the resistant animals have an increased number of copies of the structural esterase gene [108],... 

Insect GSH-S-transferases have received a good deal of attention in recent years because of their ability to catalyze the dealkylation and dearylation of a wide variety of organophosphorus insecticides (3,6,41) (Figure 8) as well as y-hexachlorocyclohexane (44). The detoxication reactions that result have been implicated in insect resistance to these insecticides (45,46). 

Newcomb, R., D., Campbell, P.M., Ollis, D., L., Cheah, E., Russel, R., J., Oaskeshott, J., G., A single amino acid substitution converts a carboxylesterase to an organophosphorus hydrolase and confers insecticide resistance on a blowfly. Proc. Natl. Acad. Sci. USA, 94, 7464-7468, 1997. 

The major agricultural pests susceptible to oxadimeter are aphids, planthoppers and leafhoppers. It is of particular interest for the control of ricehoppers which became resistant to carbamate and organophosphorus insecticides. 

The red spider (Tetranchus urticae, Koch) was a major pest on the hop but with the use of organophosphorus insecticides it virtually disappeared. However, resistant strains appeared in the late 1960s which responded to... 

In some cases, insect species can develop resistance to organophosphorus insecticides, and this resistance has appeared in those species most intensively attacked. Mixtures of insecticides are sometimes far more effective than the sum of the individual component toxicities when used separately. This effect is known as potentiation. The reasons for potentiation are not fnUy understood but they may be connected with the exhaustion of some metabolising enzyme by one insecticide, leaving the other insecticide to work freely. 

Insects have acquired resistance to organochlorine compounds, such as DDT and BHC, developed as agricultural and hygienic insecticides after World War II. This insect resistance was also acquired to subsequent organophosphorus compounds and carbamate insecticides. Photostable pyrethroids have been developed for outdoor use because pyrethroids were found to be effective against these resistant pests. As a matter of course, these pyrethroids are also effective against sanitary pests however, problems associated with safety and chemical residues indoors must be resolved. 

Resistance to insecticides has drawn global attention since the Korean War in 1950 when the mass use of organic synthetic insecticides, such as DDT and BHC, against agricultural pests and sanitary pests became common. Organophosphorus compounds and carbamates were used thereafter, but invited problems of safety concerns and insect resistance. Synthetic pyrethroids were watched with keen interest as alternatives and have become used widely not only for sanitary pests but also agricultural pests. The development of resistance to synthetic pyrethroids is also not a rare phenomenon and has spread all over the world. 

Insect resistance and environmental pollution due to the repeated application of persistent synthetic chemical insecticides have led to an Increased interest in the discovery of new chemicals with which to control Insect pests. Synthetic insecticides, including chlorinated hydrocarbons, organophosphorus esters, carbamates, and synthetic pyrethroids, will continue to contribute greatly to the increases in the world food production realized over the past few decades. The dollar benefit of these chemicals has been estimated at about 4 per 1 cost (JJ. Nevertheless, the repeated and continuous annual use in the United States of almost 400 million pounds of these chemicals, predominantly in the mass agricultural insecticide market (2), has become problematic. Many key species of insect pests have become resistant to these chemicals, while a number of secondary species now thrive due to the decimation of their natural enemies by these nonspecific neurotoxic insecticides. Additionally, these compounds sometimes persist in the environment as toxic residues, well beyond the time of their Intended use. New chemicals are therefore needed which are not only effective pest... 

Another important problem is the development of insects resistant to insecticides. This often arises as a result of increased levels of carboxylesterases which hydrolyze both organophosphates and car-baryl.h/1 A mutation that changed a single active site glycine to aspartate in a carboxylesterase of a blowfly changed the esterase to an organophosphorus hydrolase which protected the fly against insecticides.)... 

---