A new bioassay technique to assess insecticide impacts on an introduced larval endoparasitoid of emerald ash borer

Management of invasive species has employed ecosystem-based strategies that focus on long-term prevention of pests or mitigation of their damage through a combination of integrated pest management tactics. Emerald ash borer (EAB) is a highly invasive insect that has devastated the ash forests across North America. Systemic insecticides are widely used for EAB management in urban areas to protect the existing ash canopy. Classical biological control with introduced natural enemies is a key strategy for managing EAB populations in natural forests. Unfortunately, when used in tandem with biological control, systemic insecticides may impact biocontrol agents. We examined the non-target effects of azadirachtin on Tetrastichus planipennisi, an introduced larval parasitoid of EAB. A bioassay protocol was developed to expose developing T. planipennisi to insecticide concentrations causing 30% and 50% mortality of EAB larvae. EAB larvae were reared first on green ash sticks, followed by a short period of development on an artificial diet amended with insecticide, and then transplanted back to green ash sticks where they were then exposed to parasitism by T. planipennisi. We found that insecticide exposure reduced EAB larval parasitism by T. planipennisi, and had effects on parasitoid sex ratio, emergence, female body size, potential fecundity, and adult longevity. Our study establishes a methodological framework to test the non-target effects of insecticide exposure on larval parasitoids for woodboring pests but suggests that integrating biological and chemical control in EAB management may have unintended consequences for the released agents.