Spirotetramat- and Thiamethoxam-Induced Sublethal Effects Increase Spread of Tomato Chlorosis Virus by Its Vector Bemisia Tabaci

Tomato chlorosis virus (ToCV) is a major tomato virus that is mainly transmitted in a semi-persistent manner by whiteflies. The Mediterranean cryptic species, Bemisia tabaci MED (known as biotype Q) is a highly efficient vector of plant pathogens, and its management is crucial to reduce ToCV occurrence in crops. The application of insecticides has been one of the most effective measures to control whiteflies; spirotetramat and thiamethoxam are notably frequently used to manage B. tabaci. However, aside from being lethal, insecticides may have sublethal effects on surviving insects, and such effects of spirotetramat and thiamethoxam have not been assessed on whiteflies yet, notably on whitefly-vectored viral transmission. In this context, low lethal concentrations (LC15) of spirotetramat and thiamethoxam against the ToCV-carrying B. tabaci MED adults were estimated, and their impact on ToCV acquisition and transmission rates by B. tabaci were evaluated. The sensibility of B. tabaci adults to spirotetramat and thiamethoxam decreased when they carried out ToCV. The LC15 of both insecticides had limited effect on ToCV acquisition percentage (although the spirotetramat enhanced it in early feeding phase). Both insecticides led to (i) increased ToCV quantities in B. tabaci with increasing feeding time on infected plants (although only after a long feeding time on plants for whiteflies exposed to LC15 of thiamethoxam), and (ii) increased B. tabaci capacity to transmit ToCV to healthy tomato plants. Spirotetramat modulated host preferences in B. tabaci; it reduced attractiveness of ToCV-infected plants for ToCV-free B. tabaci, and reduced attractiveness of ToCV-free plants for ToCV-carrying B. tabaci. Out study show that the use of spirotetramat may be used to optimize the management of B. tabaci and ToCV.