Differential influence of temperature on the toxicity of three insecticides against the codling moth Cydia pomonella (L.) and two natural enemies

Insecticide toxicity may strongly vary with temperature, and interspecific differences have been commonly reported for this relationship. A differential influence of temperature on insecticide toxicity between pests and their natural enemies may have important consequences on biological control in a global warming context. This study aimed to investigate cross effects between temperature and three insecticides-i.e., chlorantraniliprole, emamectin and spinosad-on the mortality of a major pest in orchards, Cydia pomonella L., and two of its natural enemies in southern France, the predatory earwig Forficula auricularia L. and the introduced parasitoid Mastrus ridens Horstmann. We observed a decreased efficiency of emamectin and spinosad with increasing temperature on mortality of codling moth, while no influence of temperature on chlorantraniliprole efficacy was observed. Increasing temperatures increased the toxicity of spinosad and chlorantraniliprole against M. ridens and only for emamectin on F. auricularia. This study provides essential insight to make recommendations for using these insecticides in combination with two natural enemies to control the codling moth in prevision of global warming. Our results suggest that the use of spinosad may become sub-optimal under higher temperatures. In contrast, chlorantraniliprole should be suitable under warmer climatic conditions to control C. pomonella and the less detrimental against F. auricularia and M. ridens. To conserve the use of biological control strategies relying on F. auricularia, alternating use of emamectin during early spring, when its toxicity is the lowest on this natural enemy, chlorantraniliprole during summer could limit resistance risks in codling moth populations and reduce the insecticides' impact on the populations of natural enemies.