Functional response of an egg parasitoid, Trichogramma chilonis Ishii to sublethal imidacloprid exposure

BACKGROUND The effectiveness of a biological control agent depends on how well it can control pests and how compatible it is with pesticides. Therefore, we reported the multigenerational effect of a commonly used insecticide, imidacloprid, on the functional response of a widely acclaimed egg parasitoid, Trichogramma chilonis Ishii, to different densities of the host Corcyra cephalonica Stainton eggs. The study investigated the outcomes of the median lethal concentration (LC50) and sublethal concentrations (LC5, LC30), along with control treatments for five continuous generations (F1 to F5). RESULTS The results showed that the F5 generation of LC30, both of the F1 and F5 generations of LC50, and the control all had a Type II functional response. A Type I functional response was exhibited for the F1 generation of LC30 and both generations of LC5. The attack rate on host eggs treated with LC5 and LC30 did not change (decrease) with the shift in the type of functional response as compared to the control. A significant increase in the searching efficiency (a) was observed in the later generation (F5) under the exposure of LC5 and LC30 imidacloprid concentrations. A lower handling time (Th) in both generations of the LC5 followed by LC30 treated individuals was observed when compared with the control and LC50 treatments. The per capita parasitization efficiency (1/Th) and the rate of parasitization per handling time (a/Th) were also considerably higher in both the generations of LC5 and LC30 than in the control and LC50, thereby implying positive effects of imidacloprid on the parasitization potential of T. chilonis. CONCLUSION Altogether, these multigenerational outcomes on the functional response of T. chilonis could be leveraged to control the intractable lepidopteran pests under the mild exposure of imidacloprid in integrated pest management (IPM) programs as well as in the mass rearing of the parasitoid, T. chilonis. © 2023 Society of Chemical Industry. Multigenerational application of sublethal imidacloprid stimulated the functional response of Trichogramma chilonis which could be leveraged to annihilate the intractable lepidopteran pests.