The whitefly, Bemisia tabaci MED (Hemiptera: Aleyrodidae), is an omnivorous agricultural pest, which causes huge economic losses to agriculture and is highly resistant to many pesticides. The overexpression of cytochrome P450 may play an important role in host adaptation and insecticide resistance in B. tabaci MED. Therefore, the present study systematically analyzed the cytochrome P450 gene family at the genome-wide level to understand its function in B. tabaci MED. Our analysis identified 58 cytochrome P450 genes in B. tabaci MED, among which 24 were novel. Phylogenetic analysis revealed broad functional and species-specific diversification in B. tabaci MED P450, suggesting the role of multiple P450 genes in detoxifying. Reverse transcription-real time quantitative PCR (RT-qPCR) showed that CYP4CS2, CYP4CS5, CYP4CS6, CYP4CS8, CYP6DW4, CYP6DW5, CYP6DW6, CYP6DZ8, and CYP6EN1 genes increased significantly after two days of exposure to imidacloprid. Interestingly, all nine genes belonged to the CYP4 and CYP6 families. A decrease in the expression of five genes (CYP6DW4, CYP6DW5, CYP6DW6, CYP6DZ8, and CYP4CS6) via RNA interference (RNAi) resulted in a significant increase in the mortalities of whiteflies when exposed to imidacloprid. These results indicate that the overexpression of the P450 genes may play an essential role in imidacloprid tolerance of B. tabaci MED. Thus, the present study provides basic information on P450 genes in B. tabaci MED, which will further help elucidate the insecticide resistance mechanism in the agricultural pest whitefly.

The thermal tolerance of Bemisia tabaci MED, an invasive whitefly species with worldwide distribution, plays an important role in its ecological adaptation during the invasion process. Heat-shock proteins (HSPs) are closely related to heat resistance. In this study, 33 Hsps (BtaHsps) were identified based on sequenced genome of B. tabaci MED belonging to six HSP families, among which 22 Hsps were newly identified. The secondary structures of a further 22 BtaHsps were also predicted. The results of RT-qPCR showed that heat shock could affect the expression of 14 of the 22 Hsps newly identified in this study. Among them, the expression level of six Hsps increased under 42 °C treatment. As the unstudied gene, BtaHsp90A3 had the highest increase rate. Therefore, BtaHsp90A3 was chosen for the RNAi test, and silencing BtaHsp90A3 by RNAi decreased the survival rate of adult B. tabaci at 42 °C. The results indicated that only a few Hsps were involved in the thermal tolerance of host whitefly although many Hsps would response under heat stress. This study conducted a more in-depth and comprehensive identification that demonstrates the evolutionary relationship of BtaHsps and illustrates the response of BtaHsps under the influence of thermal stress in B. tabaci MED.