Toxicity by contact of Bordeaux mixture but no behavioral responses of the egg parasitoid Trichogramma cordubensis

Abstract

The increasing use of pesticides is recognized as a threat to pest natural enemies. We investigated the effects of Bordeaux mixture, a fungicide widely used in viticulture, on Trichogramma cordubensis, a biological control agent used against the major vineyard pest Lobesia botrana. The lethal and sublethal effects of 20 g.L⁻¹ Bordeaux mixture on T. cordubensis were studied. To assess the potential persistence of Bordeaux mixture, each experiment was conducted at four different time scales after pesticide application. A first experiment aimed to assess the effects of surface contaminations to Bordeaux mixture on the longevity of T. cordubensis, which was reduced by 26 % when exposed to the fungicide. A second experiment aimed to assess the oviposition dynamics of T. cordubensis during the three first days after its emergence in contaminated or unexposed environments. No differences in oviposition were observed when T. cordubensis was exposed to Bordeaux mixture. A third experiment aimed to assess the oviposition choices of T. cordubensis between hosts on either contaminated or unexposed surfaces. No evidence of an oviposition deterrence was detected. Overall, surface contact with Bordeaux mixture was found harmless on T. cordubensis life parameters. Time after fungicide applications did not differently impact our results on longevity and behavior. However, time after both control and pesticide applications may have led to altered micro-environmental conditions affecting T. cordubensis’ development. This study suggests that T. cordubensis inability to discriminate against a copper contaminated environment is a crucial factor in enhancing its effectiveness as a biological control agent.