Two novel sodium channel mutations associated with resistance to indoxacarb and metaflumizone in the diamondback moth, Plutella xylostella

Abstract

Indoxacarb and metaflumizone belong to a relatively new class of sodium channel blocker insecticides (SCBIs). Due to intensive use of indoxacarb, field-evolved indoxacarb resistance has been reported in several lepidopteran pests including the diamondback moth, Plutella xylostella, a serious pest of cruciferous crops. In particular, the BY12 population of P. xylostella, collected from Baiyun, Guangdong province of China in 2012, was 750-fold more resistant to indoxacarb and 70-fold more resistant to metaflumizone compared with the susceptible Roth strain. Comparison of cDNA sequences encoding the sodium channel genes of Roth and BY12 revealed two point mutations (F1845Y and V1848I) in the 6th segment of domain IV of the PxNav protein in the BY population. Both mutations are located within a highly conserved sequence region that is predicted to be involved in the binding sites of local anesthetics and SCBIs based on mammalian sodium channels. A significant correlation was observed among ten field-collected populations between the mutant allele (Y1845 or I1848) frequencies (1.7% to 52.5%) and resistance levels to both indoxacarb (34- to 870-fold) and metaflumizone (1- to 70-fold). The two mutant alleles were never found to co-exist in the same allele of PxNav, suggesting that they arose independently. This is the first time that sodium channel mutations have been associated with high levels of resistance to SCBIs. F1845Y and V1848I are molecular markers for resistance monitoring in the diamondback moth and possibly other insect pest species.

The Receptor Site and Mechanism of Action of Sodium Channel Blocker Insecticides

“…However, the same substitution F 4i15 A in a cockroach sodium channel, BgNa v 1-1a, did not reduce the potency of both DCJW and metaflumizone (17). Remarkably, one of the two mutations from the indoxacarb-resistant diamondback moth populations was a tyrosine substitution of F 4i15 , which reduced the action of both DCJW and metaflumizone on BgNa v 1-1a channels expressed in Xenopus oocytes (7,8). Furthermore, mutation of the tyrosine residue, Y 4i22 , to alanine in Na v 1.4 channels resulted in a significant increase in the potency of indoxacarb, DCJW, and RH3421 (16), and the same substitution, Y 4i22 A, also enhanced the action of metaflumizone on BgNa v 1-1a channels (17).…”

“…Two mutations, F1845Y and V1848I, in the sodium channel of the diamondback moth, Plutella xylostella (7), have been confirmed to reduce the SCBI sensitivity of cockroach sodium channels expressed in Xenopus oocytes (8). Therefore, the two mutations could be used as molecular markers for resistance monitoring in-field populations of the diamondback moth and possibly other pest species.…”

Molecular Mechanism of Action and Selectivity of Sodium Ch annel Blocker Insecticides

“…The novel chemistry and target site of SCBIs make this class invaluable for controlling insect pests, particularly those that have become resistant to other classes of insecticides. Target site-mediated resistance has been documented in a few populations of P. xylostella in China [88, 89], and it is only a matter of time until this happens again in other insect species. Therefore, further studies are necessary to understand the mechanisms through which SCBIs inhibit VGSCs and the molecular determinants that mediate these interactions.…”

“…Importantly, the first report of VGSC mutations causing resistance to SCBIs was recently published. Populations of the diamondback moth ( Plutella xylostella ) from Baiyun, Guangdong Province in China have VGSCs bearing one of two point mutations in IVS6 that were associated with 750-fold and 70-fold resistance to indoxacarb and metaflumizone, respectively, in these insects [88]. One of these sites, F 4i15 (F1845 in the diamondback moth) has been shown to be highly important for SCBI activity in mammalian VGSCs, but unimportant in cockroach VGSCs [55, 57, 58].…”

“…Mutations F 4i15 A in BgNa v 1-1 or Y 4i22 A in Na v 1.4, like V 4i18 A in BgNa v 1-1, increased sensitivity to SCBIs, suggesting that these residues may not be involved in binding of SCBIs [55, 57, 58]. These conclusions, however, must now be reconsidered since natural mutation at these residues to isoleucine or tyrosine confers resistance to SCBIs in field populations of P. xylostella [88, 89]. …”