Pretreatment with sublethal concentrations (LC10) of three insecticides (chlorfenapyr, dinotefuran, and spinosad) enhanced tolerance to a lethal dose of the respective insecticide in the Western flower thrips, Frankliniella occidentalis. To identify genes responding to sublethal treatment with insecticides, transcriptome analysis was conducted for thrips treated with LC10 of the three insecticides. When based on a fold change >1.5 or < -1.5 as a selection criterion, 199 transcripts were commonly up-regulated, whereas 31 transcripts were commonly down-regulated following all three insecticide treatments. The differential expression levels of representative genes were validated by quantitative PCR. Most over-transcribed transcripts could be categorized as basic biological processes, such as proteolysis and lipid metabolism. Detoxification genes, such as one glutathione S transferase S1, three UDP-glucuronosyltransferases, four CYP450s, and one ABC transporter G family member 20, were commonly overexpressed in all three insecticide-treated groups. Knockdown of the five representative commonly overexpressed genes via ingestion RNA interference increased mortalities to all the three test insecticides, supporting their common role in tolerance induction. In contrast, three C2H2-type zinc finger-containing proteins were significantly down-regulated in all insecticide-treated thrip groups. Since the tested insecticides have distinct structures and modes of action, the roles of commonly expressed genes in tolerance were discussed.
Keywords: Cytochrome P450s; Insecticide; Sublethal dose; Tolerance; Transcriptome analysis; Western flower thrips.
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