Sublethal imidacloprid impairs predatory performance of Orius similis against Frankliniella occidentalis across exposure routes and generations.

BACKGROUND: Sublethal pesticide risk to biological control agents is often judged by survival alone, although predators that survive exposure may still lose predatory performance. Here, we quantified the functional response of F1 and F2 Orius similis (third- to fifth-instar nymphs and male and female adults) to second-instar Frankliniella occidentalis after exposure to imidacloprid at the lethal concentrations causing 10% or 20% mortality (LC10 and LC20, respectively) through residual contact or prey-mediated ingestion. RESULTS: All stages retained a Holling type II response, but the magnitude and expression of impairment were strongly stage-, route-, concentration-, and generation-dependent. Fifth-instar nymphs and adults contributed most to prey suppression, whereas younger nymphs were most sensitive to performance loss. Residual contact tended to increase handling time, especially in younger nymphs, whereas prey-mediated ingestion more consistently reduced attack rate; both routes affected multiple functional-response parameters. Some control-standardized deficits were evident in the F2 generation, particularly in younger nymphs. CONCLUSION: Sublethal imidacloprid eroded the predatory performance of O. similis in a route-specific and generation-dependent manner during continuous multigenerational exposure, indicating that compatibility with this predator should be judged using functional endpoints in addition to survival in integrated pest management programs. © 2026 Society of Chemical Industry.