Identification of glutathione S-transferases in Bemisia tabaci (Hemiptera: Aleyrodidae) and evidence that GSTd7 helps explain the difference in insecticide susceptibility between B.tabaci Middle East-Minor Asia 1 and Mediterranean

The Bemisia tabaci (Gennadius) (Hemiptera:Aleyrodidae) species complex includes invasive and destructive pests of field crops, and the sibling species MEAM1 and MED are its two most damaging members. Previous research indicated that the replacement of Middle East-Minor Asia 1 (MEAM1) by Mediterranean (MED) as the dominant B.tabaci species in China can be mainly attributed to MED's greater tolerance to insecticides. Glutathione S-transferases (GSTs) play important roles in the detoxification of hydrophobic toxic compounds. To increase our understanding of differences in insecticide resistance between B.tabaci MEAM1 and MED, we searched the genomic and transcriptomic databases and identified 23 putative GSTs in both B.tabaci MEAM1 and MED. Through measuring mRNA levels of 18 of the GSTs after B.tabaci MEAM1 and MED adults were exposed to the insecticide imidacloprid, we found that the expression levels were increased more in B.tabaci MED than in MEAM1 (in particular, the expression level of GST-d7 was increased by 4.39-fold relative to the control). Knockdown of GST-d7 in B.tabaci MED but not in B.tabaci MEAM1 resulted in a substantial increase in the mortality of imidacloprid-treated adults. These results indicate that differences in GST-d7 may help explain why insecticide tolerance is greater in B.tabaci MED than in B.tabaci MEAM1.