Cythochrome P450-mediated dinotefuran resistance in onion thrips, Thrips tabaci

Onion thrips, Thrips tabaci, have developed resistance to many insecticides, and over the last decade, resistant populations have spread widely across Japan. The cytochrome P450 (CYP) family, a widely conserved detoxification enzyme that metabolizes xenobiotics such as insecticides and phytochemicals, is believed to play important roles in the development of resistance in T. tabaci. However, CYPs involved in insecticide resistance in T. tabaci remain unclear. To comprehensively identify CYPs in T. tabaci, the genome sequences of the thelytokous T. tabaci (ANO strain) were constructed, and 18,965 genes (protein coding) were predicted. We identified 127 CYP genes in the predicted gene set by manual curation, and 38 of these CYP genes belonged to the CYP3 clan, including genes from the CYP6 family, which is one of the most important CYP families involved in resistance to neonicotinoids in many insect pests. To identify the CYPs involved in resistance to dinotefuran, which is one of the neonicotinoids used to control T. tabaci, RNA sequencing of dinotefuran-resistant and dinotefuran-susceptible strains was performed. Results revealed that, TtCYP3652A1, which belongs to the thrips-specific CYP3652A subfamily in the CYP3 clan, was significantly upregulated in the resistant strain. In vitro CYP metabolism assays using insect cells were conducted for TtCYP3652A1 and five highly expressed CYP6 genes. Only TtCYP3652A1 significantly metabolized dinotefuran, which is considered to contribute to detoxification of dinotefuran. As no amino acid mutations were identified in the known target-site genes of neonicotinoids, TtCYP3652A1 was considered to be the main factor involved in the resistance to dinotefuran.