Abstract
Simple SummaryThe cotton aphid, Aphis gossypii Glover, is a notorious pest in cotton and cucurbit fields. The control of A. gossypii has typically relied on the application of chemical insecticides. Sulfoxaflor is the first commercially available sulfoximine insecticide, which exhibits great efficacy against sap-feeding insect pests and has been applied as an alternative insecticide for controlling of A. gossypii in China. Consequently, A. gossypii quickly developed resistance to this insecticide. Hence, in this study, to clarify the potential detoxifying roles of UGTs (one of the phase II detoxification enzymes) in resistance of A. gossypii against sulfoxaflor, the synergistic effects of two synergists (sulfinpyrazone and 5-nitrouracil) against sulfoxaflor were investigated using the susceptible and laboratory-established sulfoxaflor resistant strain (SulR), and the expression levels of 15 UGT genes were determined by qRT-PCR. Furthermore, the involvement of highly upregulated UGTs in sulfoxaflor-resistant strain was functionally tested by RNA interference (RNAi). Our results suggest that overexpression of UGTs contributes to sulfoxaflor resistance in A. gossypii, which should be useful for understanding sulfoxaflor resistance mechanisms.UDP-glycosyltransferases (UGTs) are major phase II detoxification enzymes that catalyze the transfer of glycosyl residues from activated nucleotide sugars to acceptor hydrophobic molecules and play very important roles in the biotransformation of various endogenous and exogenous compounds. Our previous studies demonstrated that UGTs participated in the detoxification of insecticides in Aphis gossypii. However, the potential roles of UGTs in A. gossypii resistance to sulfoxaflor are still unclear. In this study, two inhibitors of UGT enzymes, sulfinpyrazone and 5-nitrouracil, significantly increased the toxicity of sulfoxaflor to a resistant strain of A. gossypii, whereas there were no synergistic effects in the susceptible strain. Based on the transcriptome sequencing results, the expression levels of 15 UGTs were analyzed by quantitative real-time PCR, and we found that seven UGT genes were highly over-expressed in a sulfoxaflor-resistant strain compared to the susceptible strain, including UGT344B4, UGT344C5, UGT344A11, UGT344A14, and UGT344L2. Further suppressing the expression of UGT344B4, UGT344C5, and UGT344A11 by RNA interference significantly increased the sensitivity of resistant aphids to sulfoxaflor, indicating that the overexpression of UGT genes is potentially associated with sulfoxaflor resistance. These results could provide valuable information for further understanding the mechanisms of insecticide resistance.
Highlights
The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a notorious pest in cotton and cucurbit fields throughout the world
Based on the transcriptome sequencing results, the expression levels of 15 UGTs were analyzed by quantitative real-time PCR, and we found that seven UGT genes were highly over-expressed in a sulfoxaflor-resistant strain compared to the susceptible strain, including UGT344B4, UGT344C5, UGT344A11, UGT344A14, and UGT344L2
Both SUL and 5-NU exhibited no significant synergism against sulfoxaflor in the susceptible strain (SS), while these two synergists significantly increased the toxicity of sulfoxaflor in the SulR strain by 2.01- and 3.78-fold, respectively (Table 2) (p < 0.05)
Summary
The cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae), is a notorious pest in cotton and cucurbit fields throughout the world It causes great economic losses both through directly feeding and indirectly by virus transmission and contamination of honeydew [1]. It is well known that insects have developed four types of resistance mechanisms to chemical insecticides: metabolic resistance, target-site resistance, penetration resistance, and behavioral resistance [22]. Among these mechanisms, the enhanced detoxification mediated by the overproduction of detoxifying enzymes, including cytochrome P450 monooxygenases (P450s), esterases (ESTs), and glutathione S-transferases (GSTs), could result in pest resistance to multiple insecticide classes [4,23,24,25,26,27]. The involvement of UDP-glycosyltransferases (UGTs) in secondary metabolism was reported in several insect pests [37,38,39,40,41]
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