Ecological risks of cadmium-contaminated non-prey food on three Trichogramma egg parasitoids

Floral resources such as nectar are essential for increasing survival and population growth of synovigenic parasitic wasps in agroecosystems. Although the bottom-up effect of cadmium (Cd) has been identified as a major ecological force influencing multitrophic interactions of synovigenic parasitoids, information on the direct effects of Cd-contaminated floral resources on the fitness of natural enemies which might impact their fitness and effectiveness are still lacking. In this study, we assessed the performance of three commonly used Trichogramma species exposed to Cd-contaminated sucrose solutions. Female survival, longevity, the female/male adult proportion, and F₁ emergence rate of T. japonicum were not affected by Cd concentrations. However, a decline in the survival rate of females, their longevity, and female/male adult proportion were observed for T. dendrolimi at high Cd concentration. No significant differences in female/male adult proporation and longevity of T. ostriniae were found at wide Cd concentration ranges. Our results suggest that Cd-contaminated nectar resources can negatively affect performance of some Trichogramma spp., indicating Cd contamination in nectar would directly reduce the potential value of these species in IPM programs. These results not only increase our understanding of interspecific variations in synovigeny of Trichogramma, but also suggest that releases of T. japonicum and T. ostriniae rather than T. dendrolimi should be considered at Cd-contaminated sites.