Multigenerational effects of cadmium stress on parasitic strategies and performance of synovigenic and proovigenic Trichogramma wasps

Soil contamination by cadmium (Cd) poses an increasing threat to agricultural ecosystems and may disrupt biological pest control mediated by natural enemies. However, the multigenerational effects of Cd stress on parasitoid reproductive strategies and performance, particularly in species with contrasting ovigeny syndromes, remain poorly understood. Here, we compared the short-term (F1) and long-term (F5) effects of host-mediated Cd exposure on the synovigenic Trichogramma cacoeciae and the proovigenic T. dendrolimi. Cadmium exposure did not shift the core oviposition rhythm of either species, demonstrating that ovigeny syndrome represents a canalized life-history trait robust to multigenerational heavy metal stress. For the synovigenic species T. cacoeciae, F1 Cd exposure extended female lifespan and elevated lifetime parasitism, consistent with a hormetic stress response; by contrast, continuous Cd exposure across 5 generations (F5) suppressed early-age oviposition and total reproductive output, reflecting cumulative physiological fitness costs. In contrast, T. dendrolimi showed no significant changes in survival, daily parasitism pattern, emergence rate, or percentage of female progeny under Cd stress, except for a reduction in total parasitism after F5 exposure. These findings demonstrate that synovigenic species exhibit greater plasticity and stage-dependent responses to transgenerational Cd stress, whereas proovigenic species appear more robust. Our results provide empirical evidence for how heavy metal pollution influences parasitoid life-history traits and fitness across generations, and offer practical guidance for selecting resilient biological control agents in Cd-contaminated agricultural landscapes.