Insecticide resistant and -susceptible

The Disposition and Biotransformation of Organochlorine Insecticides in Insecticide-Resistant and -Susceptible Mosquitofish... 

Figure 1. Cytochrome P-450 contents in liver microsomes from insecticide-resistant and -susceptible mosquitofish...

Figure 2. Specific activity of NADPH-Cytochrome c reductase in liver microsomes from insecticide-resistant and -susceptible mosquitofish. A unit (U) of enzyme activity is defined as 1 pmol product formed/min.

The development of strains resistant to insecticides is an extremely widespread phenomenon that is known to have occurred in more than 200 species of insects and mites, and resistance of up to several 100-fold has been noted. The different biochemical and genetic factors involved have been studied extensively and well characterized. Relatively few vertebrate species are known to have developed pesticide resistance and the level of resistance in vertebrates is low compared to that often found in insects. Susceptible and resistant strains of pine voles exhibit a 7.4-fold difference in endrin toxicity. Similarly pine mice of a strain resistant to endrin were reported to be 12-fold more tolerant than a susceptible strain. Other examples include the occurrence of organochlorine insecticide-resistant and susceptible strains of mosquito fish, and resistance to Belladonna in certain rabbit strains. 

In leaf dip bioassuys, PBO was lethal at doses of between 60 and 600 ppm to early in stars of four strains of insecticide-resistant and susceptible Battista (abaci (Table 14,2). PBO also killed whitefly adults, but only when insects were exposed to fresh residues of over 1000 ppm. After 24 hours the toxicity of these residues declined markedly (G. Devine, unpublished). 

Chambers, J.E. and J.D. Yarbrough. Organophosphate degradation by insecticide-resistant and susceptible populations of mosquitofish (Gambusia affinis). Pesti. Biochem. Physiol. 3 312-322, 1973. 

Yu, S.J. and Terriere, L.C. 1979. Cytochrome P-450 in insects. 1. Differences in forms present in insecticide resistant and susceptible house flies. Pest. Biochem. Physiol, 12, 239-248. 

Kennedy, G. G. and R. R. Farrar, Jr. 1987. Response of insecticide-resistant and susceptible Colorado potato beetles, Leptinotarsa decemlineata to 2-tridecanone and resistant foliage the absence of cross resistance. Entomol. Exp. Appl. 45 187-192. 

CK Kikankie, BD Brooke, BGJ Knols, LL Koekemoer, M Farenhorst, RH Hunts, MB Thomas, and M Coetzee. The infectivity of the entomopathogenic fungus Beauveria bassiana to insecticide-resistant and susceptible Anopheles arabiensis mosquitoes at two different temperatures. Malar. 7. 9 71,2010. 

The picture changed rapidly after introduction of the potent and persistent compound, DDT. DDT resistance appeared quickly, worldwide, and in several species, following the first report in 1947 (41). New insecticides were introduced steadily, providing better control of both resistant and susceptible insects, but most new products eventually suffered the same fate. The number of species showing resistance to one or more toxicant doubled about every six years between 1948 and 1983 (31). 

This enzyme, purified from aphids (24). was very slow in hydrolyzing paraoxon compared to mammalian arylester hydrolases (Table III) however, it was twice as fast in recovery from paraoxon inhibition compared to a porcine carboxylester hydrolase (35) and >300 times faster than monomeric carboxylester hydrolase of rabbit liver (26). No qualitative differences were found in the enzyme, E4, isolated from resistant and susceptible aphids E4 was one of seven electrophoretic forms of hydrolases observed (34). Recovery indicates that resistance is due to both reaction with the insecticide and a very slow turnover, or catalysis. A similar mechanism of was observed with paraoxon in resistant green rice leafhoppers (37). 

Wheelock GD, Scott JG (1992) The role of cytochrome- P450IPR in deltamethrin metabolism by pyrethroid-resistant and susceptible strains of house-flies. Pestic Biochem Physiol 43 67-77 Wheelock GD, Shan G, Ottea J (2005) Overview of carboxylesterases and their role in the metabolism of insecticides. J Pestic Sci 30 75-83... 

Insecticide resistance has been shown to involve three principal mechanisms, i.e., enhanced detoxification, decreased penetration, and target site insensitivity. Usually these factors interact with one another so that the effect of each is magnified. There are two kinds of insects, those that are already tolerant and those that are susceptible at first but become resistant later. The former may be tolerant because of behavior, morphology, or detoxification capacity. The latter become resistant because of selection of individuals that possess higher levels of detoxification enzyme activity and which are thus able to survive and produce progeny. All of these aspects of resistance will be discussed at length in Chapter 10. 

Decreased uptake as a mechanism of resistance was also observed in houseflies resistant to organochlorine, organophosphate, and carbamate insecticides. Resistant strains had higher total lipids, monoglycerides, diglycerides, fatty acids, sterols, and phospholipids in the cuticle than did the susceptible strain (Patil and Guthrie, 1979). 

Synergism in a susceptible strain can be shown to overcome naturally occurring breakdown mechanisms. Some forms of resistance result from an increase in such breakdown mechanisms. Resistance may also be due to a restriction on the speed of entry of an insecticide, thereby exaggerating the effect of normal levels of breakdown enzymes, e.g. pen (Farnham, 197.3). The scope of the use of synergists in cases of resistance and the possibility thal a wider range of insecticides could become available for use was reviewed by Oppcnoorth (1971). 

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