A novel bioassay to assess the non-target impacts of insecticide exposure on a larval endoparasitoid of the emerald ash borer

Pest management strategies for invasive species like the emerald ash borer (EAB) must combine chemical control with biological control agents to protect vulnerable hosts. When used in tandem with biological control agents, however, systemic insecticides may impact the fitness of biological control agents, thus reducing their effectiveness. Systemic insecticides are used for EAB management in urban forests across North America, while classical biocontrol with introduced natural enemies has been an important tactic for managing EAB in natural forests in North America. We tested the non-target effects of azadirachtin on Tetrastichus planipennisi Yang, a larval parasitoid of EAB introduced to North America. A novel bioassay protocol was developed whereby EAB larvae were initially reared on host material in the laboratory and then temporarily transferred to an artificial EAB diet containing azadirachtin followed by exposure to parasitism by T. planipennisi. Exposure to azadirachtin at concentrations causing 30% and 50% mortality in EAB larvae reduced EAB larval parasitism by T. planipennisi. Exposure to azadirachtin also reduced T. planipennisi's sex ratio, adult emergence, female body size, potential fecundity, and adult longevity. These results suggest there are negative interactions between systemic insecticides and EAB biological control agents, which present challenges for the integration of tactics for long-term EAB management.