Effects of neonicotinoid insecticides on spider mites

Neonicotinoid insecticides are often used as a seed treatment for row crops. Their systemic nature allows for targeted effects on herbivores, while reducing exposure to other arthropods, humans, and the environment. Neonicotinoid insecticides have become ubiquitous in soybean production, and it is important to understand how these insecticides affect non-target arthropods. Spider mites (Acari: Tetranychidae), which are not susceptible to neonicotinoids, are of particular interest because they have been shown to increase in abundance after neonicotinoid use in other plant systems. The goal of this research was to document the propensity for spider mite outbreaks on soybean plants after neonicotinoid insecticides are applied. In greenhouse experiments, we tested the effect of thiamethoxam seed treatments, as well as water and temperature stress on spider mite abundance and fecundity. We found that spider mites tended to be more abundant on plants exposed to the neonicotinoid insecticides only when plants had undergone a period of stress. We also found that seed treatment applications of thiamethoxam affected the number of leaves produced by plants, indicating a possible impact on plant fitness. This research provides valuable insights into the relationship between neonicotinoid insecticides, spider mites, and plant physiology, and has important implications for sustainable management of spider mites and other herbivores in soybean fields.