Cadmium (Cd) exposure through Hyphantria cunea pupae reduces the parasitic fitness of Chouioia cunea: A potential risk to its biocontrol efficiency

Heavy metal contamination has been regarded as an environmental variable that affects the efficiency of pest biological control, but the parasitic fitness of parasitoids under heavy metal stress is poorly understood. Herein, the effect of Cd exposure through the host pupa of Hyphantria cunea on the parasitic fitness of Chouioia cunea was investigated, and the mechanism by which Cd exposure affects the interaction between H. cunea and C. cunea from the perspective of innate immunity in host insect and the oxidative status in the parasitoid offspring was explored. Our results indicated that Cd can be transferred from the H. cunea pupae to the parasitoid offspring, and the transfer coefficient reflected biological amplification. There were no significant differences in the rates of parasitism success and offspring emergence between the untreated and Cd-treated groups. However, after parasitizing Cd-accumulated pupae, the parasitic fitness of offspring wasps (e.g., the number, individual size and life span) decreased significantly. Under Cd exposure, the cellular and humoral immunity of H. cunea pupae decreased significantly. Compared with the untreated group, the H2O2 content of parasitoid offspring in the Cd-treated group was significantly increased. Cd exposure significantly inhibited superoxide dismutase activity in parasitoid offspring, but the contents of ascorbic acid and glutathione were significantly increased by Cd stress. Taken together, these results indicate that Cd exposure reduces the cyclic utilization efficiency of C. cunea on H. cunea pupae. The oxidative status of parasitoid offspring triggered by Cd exposure could be responsible for the reduced parasitic fitness of C. cunea on Cd-accumulated H. cunea pupae.