Comparative Toxicity of Bordeaux Mixture by Ingestion and Cuticular Contact Under Climate Change Conditions on Trichogramma cordubensis

ABSTRACT In the face of environmental contamination to copper, mainly resulting from frequent copper‐based fungicide applications, it is crucial to understand the side effects of these pesticides on non‐target organisms to favor sustainable pest management. Pest natural enemies are indeed severely exposed to copper fungicides through external physical contact and by ingestion. In this study, we assessed the effects of Bordeaux mixture applications on the longevity of the biological control agent Trichogramma cordubensis (Vargas and Cabello, 1985) (Hymenoptera: Trichogrammatidae). The first set of experiments aimed to evaluate the effective doses of Bordeaux mixture contamination by using eight doses from 0 g.L −1 to 160 g.L −1 . When ingesting honey contaminated with Bordeaux mixture the longevity of T. cordubensis was strongly reduced. Conversely, cuticular contact with Bordeaux mixture, without ingestion, had no effect on T. cordubensis longevity. The second set of experiments examined how the effects of Bordeaux mixture on T. cordubensis longevity were modulated by global warming conditions, under two fluctuating climatic regimes simulating current and future conditions in Burgundy, France. These experiments used effective doses obtained after the first experiments. Similarly to the first experiments, Bordeaux mixture ingestion led to strongly reduced longevity, whereas cuticular contact had no effects on T. cordubensis longevity. Warming conditions reduced T. cordubensis longevity by 36% after both ingestion and cuticular contact with Bordeaux mixture, with no statistical interaction with Bordeaux mixture. Ingesting Bordeaux mixture was considered to be slightly to moderately harmful, significantly reducing the longevity from 40% to 81% with increasing concentrations, whereas cuticular contact with Bordeaux mixture was harmless to T. cordubensis . This study sheds new light on the side effects of metal‐based fungicides on natural enemies and their subsequent effects on biocontrol programs. It suggests that increasing temperatures should have deleterious effects on Trichogramma species, regardless of fungicide contamination by Bordeaux mixture.