Heavy metals used as fungicide may positively affect Trichogramma species used as biocontrol agents in IPM programs

The use of biological control agents in Integrated Pest Management programs has increased in the last decades, but may be affected by antagonistic effects generated by the accumulation of some pesticides and other chemicals. The objective of this study was to evaluate the performance of Trichogramma cordubensis (Hymenoptera: Trichogrammatidae), a candidate agent to control grapevine moths, when these beneficial insects are exposed to copper treatments through trophic accumulation. A generation of the host Lobesia botrana (Lepidoptera: Tortricidae) was reared on a diet with different concentrations of copper from Bordeaux mixture incorporated into the diet. The host eggs laid by these females were then exposed to female parasitoids. Our results showed that copper consumed by the host parental generation had no effects on the parasitism rate but had positive effects on the emergence rate and size of emerging parasitoids at the highest copper concentration. These effects of copper on parasitoids may be due to stress effects of copper on the host parental generation, linked with a trade-off between development and defenses leading to a reduced immunity in their host eggs. Another hypothesis may be that copper has been transferred into the host eggs at potentially beneficial concentrations for parasitoids due to detoxification mechanisms of the hosts' mothers facing a chemical stress. These positive effects of copper pesticides on parasitoids have been observed at the highest copper concentration, consistent with real exposure conditions in the field. This study thus highlights potential synergetic effects between pesticides and natural enemies.