An independent occurrence of the chimeric P450 enzyme CYP337B3 of Helicoverpa armigera confers cypermethrin resistance in Pakistan

Variation in P450-mediated fenvalerate resistance levels is not correlated with CYP337B3 genotype in Chinese populations of Helicoverpa armigera

“…And higher expression in resistant strains has been demonstrated for 12 (from the CYP4, CYP6, CYP9, CYP332 and CYP337 families) of 30 H. armigera CYP genes tested [37]. While Rasool et al [24] have shown that elevated levels of such P450s do not necessarily contribute to resistance, there is in fact further evidence for four of them suggesting that those four at least may do so. One of these is CYP337B3, as already discussed.…”

“…Rasool et al [24] showed that seven fold resistance to cypermethrin in Pakistani H. armigera could be explained by the CYP337B3v2 P450 gene/enzyme system. This variant is also at high frequency in our Chinese populations and likely contributes to some degree to the fenvalerate resistance we have found in this material.…”

“…Sequencing of 10-12 B3 homozygotes from each field population (Figs. 2 and S1) showed that the great majority (69 out of 72) had the B3v2 allele which Rasool et al [24] showed was associated with 7 fold resistance to cypermethrin in a Pakistani strain. The B3v1 allele commonly found in Australia was not seen in any of our samples.…”

“…QTL mapping between a fenvalerate susceptible and resistant Australian strain (TWB) found the CYP337B3v1 allele to be absent from susceptible backcross individuals but present in those showing~50 fold resistance. Subsequently Rasool et al [24] have associated a different allele, CYP337B3v2 (which has a slightly different cross over site), with~7 fold resistance to cypermethrin in a Pakistani population.…”

Over-expression of CYP6A2 is associated with spirotetramat resistance and cross-resistance in the resistant strain of Aphis gossypii Glover

“…Previous research indicated that the major resistance mechanism to cypermethrin in the cypermethrin-resistant strain of houseflies is due to the overexpression of CYP6D1 [34]. In addition, CYP337B3 in the fenvalerate-resistant Helicoverpa armigera could metabolize fenvalerate and confer cross-resistance to cypermethrin due to its capability of metabolizing alpha-cypermethrin and cypermethrin to the main intrinsically nontoxic metabolite 4′-hydroxycypermethrin [35,36]. Thus, the high levels of cross-resistance to alpha-cypermethrin and bifenthrin in resistant aphids may be caused by the overexpression of CYP6A2.…”