Carbaryl resistance

McCord, E., Jr. and Yu, S.J., Mechanisms of carbaryl resistance in the fall armyworm, Spodoptera frugiperda (J. E. Smith), Pestic. Biochem. Physiol., 27,114,1987. 

A single gene may be responsible for the resistance, and in these cases the level of resistance can be quite high. Well-known examples are the 2000-fold resistance to organophosphates in spider mites, spinosad resistance in western flower thrips, DDT resistance in houseflies, and dieldrin resistance in several Diptera. In other cases, multiple genes are clearly involved in the resistance. Examples are carbaryl resistance in houseflies (Georghiou, 1972), carbaryl resistance in fall army worms (Yu et al., 2003), and malathion resistance in oriental houseflies (Yeoh et al., 1981). 

Amblyselus fallacls. A. fallacls Is an Important predator of spider mires in deciduous orchards In the eastern U.S.A. and Its field-developed resistance to OP Insecticides has been augmented by laboratory selection for carbaryl and permethrln resistances (26-27). The carbaryl resistance appeared unstable and Is not currently being used. Permethrln resistance Is polygenlcally determined and the selected strains have undergone field trials... 

Development time, fecundity, sex ratio, mating compatibilities and competition, diapause, persistence of the carbaryl resistance, and the capability to control spider mite populations under carbaryl sprayed and unsprayed conditions were evaluated. The resistant strain did not differ significantly from the susceptible strains tested In the absence of carbaryl treatment. 

Figure 3. The coninon green lacewing Chrysoperla camea preys, as inmatures, on small arthropods. C.carnea was selected for carbaryl resistance in the laboratory. (Photo by Jack Kelly Clark, U.C. Cooperative Extension.)...

With the introduction of the carbamate insecticides in 1956, resistance to carbaryl appeared between 1963 and 1966 in an orchard leafroller in New Zealand, in the cotton leafworm (Spodoptera) of Egypt, and in Heliothis virescens (the so-called tobacco bud-worm) on American cotton (Table VI). Resistance developed to OP compounds had already given some cross-tolerance to carbamates... 

The mechanism of carbamate-resistance, formerly considered to be enhanced hydrolysis (e.g. carbaryl to 1-naphthol), was found to derive almost exclusively from hydroxylation at various points on the molecule, not only the aromatic leaving group but also the N-methyl on the carbamate (Fig. 3), as well as some desmethylation for good measure (14). Pyrethrin-resistance, at first considered to be due to hydrolysis of the alcohol-acid linkage, was also found to be due to an oxidation, occurring at the transmethyl group of the isobutenyl side-chain of the chrysanthemic acid (15). 

Figure 3. Detoxicative mechanisms imparting carbamate-resistance (e.g. to carbaryl)...

Successive resistances have driven control of the Boophilus cattle ticks all the way to OP compounds, and from them to chlor-phenamidine (chlordimeform) although it has been recently found that carbaryl is effective in cattle dips if synergized with piperonyl butoxide. The two-spotted mite has gone through a fantastic sequence of acaricides, the only ones to which resistance has not yet been reported being Pentac and the organo-tin compound Plictran. 

The development of resistance by certain insect species to chlorinated hydrocarbon insecticides aroused research into alternative chemical classes of compounds. This research led to the development of the carbamates as useful broad-spectrum insecticides. The best known of this class is carbaryl (Sevin), which has emerged as one of the most extensively used insecticides. 

An example taken from the work of Georghiou (1972) on the housefly is illustrated in Figure 10.5. In this case, the combination of chromosome 2, which confers a 3.2-fold resistance to carbaryl because of enhanced detoxification (P450s) (strain R-2), and chromosome 3, which confers a 1.7-fold resistance because of reduced penetration (strain R-3), increases resistance 50-fold. The addition of chromosome 5 to the combination (strain R-235) increases resistance further, to nearly the original level of the parental R strain. 

Figure 10.5 Resistance to carbaryl plus piperonyl butoxide in the ronnel-resistant strain of the housefly, five derivative strains with single chromosomes, and their combinations. (From Georghiou, G.P., Annu. Rev. Ecol. Syst., 3,133,1972. With permission.)...

Metabolic resistance mechanisms are still the most widely encountered causes for OP and carbamate resistance. Yet, after the first few cases of target site insensitivity were reported in the early 1970 s in mites and ticks, many such cases have been found also in insects. Resistance can also be enhanced by a decreased rate of penetration through the integument. This resistance mechanism by itself is of minor importance, but provides an increased opportunity for detoxification. A 50-fold increase in resistance to carbaryl was seen in a house fly strain, in which a gene for reduced penetration had been combined (by selective breeding) with a gene for increased detoxification (5). 

Phenylcarbamates and Carbanilates. The phenylcarbamate pesticides are much more water soluble than the substituted anilines (Table VIII), but despite the higher solubilities they are also immobile in soil systems. All are herbicides except for carbaryl which is an insecticide. Chlorpropham and terbutol resisted leaching, and propham leached only slightly 137, 143, 144, 343, 344, 345, 346), In herbicide mobility studies in soils, Harris (151) ranked chlorpropham with the substituted anilines as having low movement. 

The carbamate derivatives, including Carbaryl, tend to be less toxic than the organophosphorus compounds. They are also readily degraded to harmless materials. Nevertheless, insects resistant to soft insecticides have also been observed. Furthermore, the organophosphorus and carbamate derivatives destroy many more nontarget pests than the chlorocarbon compounds do. The danger to earthworms, mammals, and birds is very high. 

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