Implication of heat-shock protein 70 and UDP-glucuronosyltransferase in thiamethoxam-induced whitefly Bemisia tabaci thermotolerance

Abstract

Temperature change is likely to have marked ecological effects on terrestrial ecosystems, including the activities of insect pests. The whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) is a serious pest of agricultural crops in temperate and tropical regions worldwide. The distribution of this threatening species includes areas and seasons with very frequent stressful temperatures, thus thermotolerance might be an important factor in the colonizing success of this species. Most attention has focused on the intrinsic mechanism of B. tabaci thermotolerance; however, whether extrinsic factors enhance their thermotolerance remain poorly understood. Outbreaks of B. tabaci have occurred in China in recent years and these outbreaks have been associated primarily with pesticide overuse, especially for thiamethoxam. This study tested whether exposure to sublethal concentrations of thiamethoxam enhances thermotolerance of B. tabaci. Thiamethoxam exposure (20 ppm at 40 °C) significantly decreased mortality (from 80% in controls to 50% at 5 h post-treatment) and increased lethal mean time (LT50) of adults by 0.8 h. We further demonstrated that transcript levels encoding heat-shock protein 70 (Hsp70) and UDP-glucuronosyltransferase (UGT) in adult females exposed to thiamethoxam were up-regulated compared with controls. RNAi silencing of both genes showed that Hsp70 and UGT were essential for B. tabaci survival and thiamethoxam-increased thermotolerance. We propose that thiamethoxam induces thermotolerance in B. tabaci by increasing the expression of genes that act in cell protection mechanisms. The significance of this study relates to the importance of understanding the influence of sublethal concentrations of insecticides on pest thermotolerance.