Abstract:

【Aim】 Gammaaminobutyric acid (GABA) is an important neurotransmitter in animal nervous system. This study aims to identify the GABA receptor (GABAR) familygenesinthewestern flower thrips, Frankliniella occidentalis, and to clarify the role of ionotropic receptor (GABA_AR) in the resistance evolution to spinosad in F. occidentalis. 【Methods】 Based on the genomeand transcriptome data of F. occidentalis, the GABAR genes were identified, cloned and analyzed with bioinformatics tools. The expression patterns of the GABA_AR subunit genes, FoRDL, FoLCCH3, and FoGRD in the spinosad susceptible strain of F. occidentalis at different developmental stages (1st-2nd instar nymphal, pupal, and adult stages), and their expression differences between the spinosad susceptible and resistant strains of F. occidentalis at the adult stage were detected by qPCR. After treatment with 0.250 and 0.400 mg/L spinosad at 24 h post RNAi of FoRDL in the 3-day-old adults of the spinosad susceptible strain of F. occidentalis, the mortality rates of F. occidentalis adults were determined by bioassay. 【Results】 Eight GABAR genes including FoRDL, FoLCCH3, FoGRD, FoGRD-like1, FoGRD-like2, FoB1, FoB2, and FoB-like (GenBank accession numbers: MH148151-MH148158) were annotated and cloned, and their ORF lengths vary from 1 080 to 3 720 bp. Phylogenetic analysis showed that GABAR genes of F. occidentalis were clustered with the corresponding genes of other insect species, indicating high conservativeness. GABA_AR subunits FoRDL, FoLCCH3 and FoGRD all have a typical nitrogen-terminal extracellular region loop structure (loop A-F) and four transmembrane regions (TM 1-4), and exon 3 of FoRDL has mutually exclusive splicing. The expression levels of FoRDL, FoLCCH3 and FoGRD in the spinosad susceptible strain of F. occidentalis increased with the developmental stage of F. occidentalis, and the expression peak occurred at the adult stage. The expression level of FoRDL in the spinosad resistant strain of F. occidentalis at the adult stage was significantly lower than that in the susceptible strain at the adult stage. After treatment with 0.250 and 0.400 mg/L spinosad following RNAi of FoRDL in the susceptible strain of F. occidentalis, the mortality rates of F. occidentalis adults decreased significantly by 55.80% and 43.00%, respectively, as compared to those of the control. 【Conclusion】 Five ionic and three metabotropic GABAR genes have been identified in F. occidentalis. FoRDL may play a role in the resistance evolution to spinosad in F. occidentalis.

Key words: Frankliniella occidentalis, γ-aminobutyric acid receptor, spinosad, insecticide resistance, RNA interference