Sublethal Effects of Four Insecticides with Different Modes of Action on Life History, Demography and Host...

Understanding how sublethal insecticide exposure affects natural enemies is crucial for sustainable pest management, yet such effects remain largely unexplored in some scelionid parasitoids, including Telenomus busseolae Gahan (Hymenoptera: Scelionidae). This study evaluated the compatibility of widely used insecticides with different modes of action-imidacloprid, indoxacarb, teflubenzuron, and chlorantraniliprole-with the biological control of the Mediterranean corn borer, Sesamia nonagrioides (Lefèbvre) (Lepidoptera: Noctuidae), by the egg parasitoid T. busseolae, a key natural enemy. Risk quotients (RQ), calculated as the ratio of field concentrations to LC₅₀ (median lethal concentration) values, indicated low acute risk for all insecticides. Sublethal effects on adult parasitoids were assessed at LC₂₅ concentrations using the age-stage, two-sex life table approach revealing significant impacts on longevity, fecundity, oviposition duration, and population growth parameters, including intrinsic rate of increase (r) and finite rate of increase (λ), with the most pronounced effects observed under imidacloprid exposure. Host exploitation remained mostly unaffected except under imidacloprid, which reduced net parasitism rate (P₀), while the transformation rate (Q_p = P₀/R₀), representing the relationship between net parasitism (P₀) and net reproductive rate (R₀) at the population level, the stable parasitism rate (ψ), representing parasitism capacity under a stable age-stage structure, and the finite parasitism rate (ω), integrating parasitism capacity with population growth to describe overall parasitism potential, were unchanged. Population projections over 60 days (three generations) suggested the greatest decline under imidacloprid exposure. These findings demonstrate that even sublethal exposure can affect parasitoid fitness, host utilization, and population trajectories, emphasizing the importance of choosing insecticides that are selective for T. busseolae to maintain effective biological control.