Transcriptome-based identification and characterization of commonly responding genes to sublethal doses of three different insecticides in the western flower thrips, Frankliniella occidentalis

Pretreatment with sublethal doses (LD₁₀) 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 LD₁₀ 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. Ingested dsRNA of the five representative commonly overexpressed genes managed to knock down their expression level from 42.4% to 80.5%. Furthermore, these dsRNA-treated thrips had increased mortalities in all the three test insecticides, supporting their common role in tolerance induction.  Since the tested insecticides have distinct structures and modes of action, the roles of commonly expressed genes in tolerance were discussed.