Relative contribution of detoxifying enzymes to pyrethroid resistance in a resistant strain of Helicoverpa armigera

Abstract

The relative contribution of oxidases and esterases to pyrethroid resistance was studied in a YS-FP strain of Helicoverpa armigera from China. The YS-FP strain was derived from a field-collected strain (YS) by 16 generations of selection with a mixture of fenvalerate and phoxim. Compared with the YS strain, the YS-FP strain showed 1850-to >7140-fold resistance to four ester-bonded phenoxybenzyl alcohol pyrethroids (fenvalerate, deltamethrin, cypermethrin and cyhalothrin), >205-fold resistance to a non-ester phenoxybenzyl alcohol pyrethroid (etofenprox) and only 19-fold resistance to an ester-bonded methylated biphenyl alcohol pyrethroid (bifenthrin). The oxidase inhibitor piperonyl butoxide eliminated most the of resistance to fenvalerate, deltamethrin, cypermethrin, cyhalothrin and etofenprox, whereas the esterase inhibitor S,S,S-tributylphosphorothioate had a small synergistic effect for fenvalerate and cyhalothrin only. This suggests that the resistance to these pyrethroids in the YS-FP strain was mainly because of enhanced oxidative detoxification. The monooxygenase activities of the midguts of sixth-instar larvae of the YS-FP strain to substrates p-nitroanisole, ethoxycoumarin and methoxycoumarin were 3.7-, 4.7-and 10-fold, respectively, compared with that of the YS strain. Glutathione S-transferase activity and esterase activity were not significantly altered in the YS-FP strain. This confirms that enhanced oxidative detoxification was a major mechanism contributing to pyrethroid resistance in the YS-FP strain.

Overexpressed esterases in a fenvalerate resistant strain of the cotton bollworm, Helicoverpa armigera

“…The degree of P450-mediated resistance to pyrethroids in the YS-FP strain from China was found to depend on the nature of the alcohol moiety in the pyrethroid structure (Yang et al, 2005). Resistance to pyrethroids in the CMR strain from China was also mainly due to enhanced oxidative metabolism, and substitution of the phenoxybenzyl group found in the alcohol moiety of most commercial pyrethroids with a polyfluorobenzyl group (eg in tefluthrin, benfluthrin and transfluthrin) overcame most of the resistance (Tan and McCaffery, 2007).…”

Gene identification and proteomic analysis of the esterases of the cotton bollworm, Helicoverpa armigera

“…Enhanced metabolism of the insecticide by detoxifying enzymes such as cytochrome P450-dependent monooxygenases, glutathione-Stransferases and carboxylesterases is responsible for a significant proportion of this resistance (Bues et al, 2005;Yang et al, 2005;Ahmad et al, 2006;Ugurlu et al, 2007).…”

Esterase-based metabolic resistance to insecticides in heliothine and spodopteran pests

“…[56][57][58] Whether this geographic variation in the strength of the associations reflects genetic differences among populations or methodological differences among investigators is moot, although some effect of genetic differences seems likely. Esterases seem to be responsible for only a few-fold resistance in Chinese populations, 54,55) whereas much higher resistance factors have been attributed to the esterases in some of the other populations. 39,42) Similarly the increase in esterase activity in the Chinese resistant strains is only a few-fold but in at least one Australian study the corresponding figure is reported to be as much as 50-fold.…”

“…The association is particularly strong in data for populations from Australia, [39][40][41][42] south and southeast Asia [43][44][45][46][47][48][49][50][51] and central Africa 52,53) and is also significant in Chinese populations, 46,54,55) although it has not been found in west African populations. [56][57][58] Whether this geographic variation in the strength of the associations reflects genetic differences among populations or methodological differences among investigators is moot, although some effect of genetic differences seems likely.…”