Association of VGSC Mutations and P450 Overexpression with Beta-Cypermethrin Resistance in Aphis gossypii Glover from a Chinese Wolfberry (Lycium barbarum L.) Field

Chinese wolfberry (Lycium barbarum L.), a specialty crop with ecological, medical, and economic value in Ningxia province of China, is subject to severe damage from Aphis gossypii Glover. Currently, A. gossypii populations show extremely high-level resistance to beta-cypermethrin in the major wolfberry planting areas in Ningxia. The specific resistance mechanisms, however, are still not known. In this work, we collected a field A. gossypii strain (HSP) from a wolfberry orchard in Ningxia in 2021 using a single-time sampling method, and its resistance to beta-cypermethrin was determined to be extremely high (994.74-fold) as compared with that of a susceptible strain (SS). Then we explored the potential resistance mechanisms from two aspects, namely, metabolic detoxification and target-site alterations. Bioassays of beta-cypermethrin with or without a synergist showed that piperonyl butoxide (PBO) significantly increased the toxicity of beta-cypermethrin (4.72-fold) to the HSP strain, while triphenyl phosphate (TPP) and diethyl maleate (DEM) exhibited no significant synergistic effects. Correspondingly, the O-demethylase activity of cytochrome P450s in the HSP strain was 1.68-fold higher than that in the susceptive strain (SS), whereas changes in carboxylesterases and glutathione S-transferases activities were unremarkable. Also, fifteen upregulated P450 genes were identified by both RNA-Seq and qRT-PCR technologies, containing eleven CYP6 genes, three CYP4 genes, and one CYP380 gene. Especially, five CYP6 genes with high relative expression levels (>3.00-fold) were intensively expressed by beta-cypermethrin induction in the HSP aphids. These metabolism-related results indicate the key role of P450-mediated metabolic detoxification in HSP resistance to beta-cypermethrin. Sequencing of voltage-gated sodium channel (VGSC) genes identified a prevalent M918L mutation and a new G1012D mutation in HSP A. gossypii. Moreover, heterozygous 918 M/L and 918 M/L + G1012D mutations were the dominant genotypes with frequencies of 60.00% and 36.67% in the HSP population, respectively. Overall, VGSC mutations along with P450-mediated metabolic resistance contributed to the extremely high resistance of the HSP wolfberry aphids to beta-cypermethrin, providing support for A. gossypii control and resistance management in the wolfberry planting areas of Ningxia using insecticides with different modes of action.