Transgenerational toxicity of imidacloprid on demography and behaviour of key larval parasitoid, Habrobracon hebetor (Say)

A successful Integrated Pest Management (IPM) program depends on using both bio agents and chemical pesticides, making it essential to consider pesticide effects on non-target organisms used in biological control. This study examines the effects of LC5, LC30 and LC50 concentrations of imidacloprid on the demographic and behavioural traits of Habrobracon hebetor (Say) across successive generations (F1 to F5). In the bioassay experiments, imidacloprid exhibited profound toxicity, with an LC50 of 40.75 mg L-1, while LC5 was 0.27 mg L-1and LC30 was 8.27 mg L-1. Notably, egg and larval development periods were significantly prolonged in F5 individuals exposed to LC5 and LC30 compared to those in F1. Key population parameters, including the net reproductive rate (R₀), gross reproductive rate (GRR) and mean generation time (T), were markedly lower in the F5 generation, particularly at LC30. Exposure to LC50 in the F5 generation resulted in extended egg, larval and pupal development durations, alongside reduced male longevity, fecundity and oviposition periods. All population parameters, except the intrinsic rate of increase (r) and finite rate of increase (λ), were significantly impacted. Additionally, walking behaviour differed significantly among individuals treated with LC5, LC30 and LC50 concentrations; while LC5 exposure notably increased walking speed, it still exerted a detrimental effect on demographic parameters overall. To minimize these adverse outcomes, optimizing the timing of pesticide application is essential to avoid antagonistic interactions with natural enemies in IPM programs.