Effect of Neonicotinoids on Bacterial Symbionts and Insecticide-Resistant Gene in Whitefly, Bemisia tabaci

SIMPLE SUMMARY: The silverleaf whitefly (B. tabaci) is an important agricultural pest damaging several agricultural and horticultural crops worldwide. Keeping in mind the status of insecticide overuse, the current experiment was designed to evaluate the sensitivity of B. tabaci towards imidacloprid and thiamethoxam (two popularly used neonicotinoids in India). The lab population of B. tabaci was found to be more susceptible to thiamethoxam compared to imidacloprid. qPCR studies revealed a higher expression of insecticide-resistant genes, CYP6CM1 and CYP6CX1, after imidacloprid treatment that might be responsible for increased resistance to insecticides. Our results also put forward the different interactions between symbionts and insecticide resistance. qPCR studies revealed thiamethoxam-treated B. tabaci populations harbored a higher amount of primary endosymbiont Portiera and a lower amount of secondary symbiont Rickettsia. ABSTRACT: The silverleaf whitefly, Bemisia tabaci (Gennadius, Hemiptera: Aleyrodidae), is a major threat to field and horticultural crops worldwide. Persistent use of insecticides for the management of this pest is a lingering problem. In the present study, the status of sensitivity of B. tabaci to two neonicotinoids, imidacloprid and thiamethoxam, was evaluated. The expression pattern of two cytochrome P450 (cyp) genes and changes in the relative amount of symbionts in insecticide-treated B. tabaci were also assessed. Quantitative PCR (qPCR) studies indicate that the CYP6CM1 and CYP6CX1 genes were always expressed higher in imidacloprid-treated whitefly, suggesting a correlation between gene expression and the insect’s ability to detoxify toxic compounds such as insecticides. In addition, the thiamethoxam-treated population harbored higher Portiera and lower Rickettsia titers, whereas the imidacloprid-treated population harbored more Rickettsia at different time intervals. Interestingly, we also examined that an increase in exposure to both the insecticides resulted in a reduction in the mutualistic partners from their insect host. These differential responses of endosymbionts to insecticide exposure imply the complex interactions among the symbionts inside the host insect. The results also provide a deeper understanding of the molecular mechanism of resistance development that might be useful for formulating effective management strategies to control B. tabaci by manipulating symbionts and detoxifying genes.