Multigenerational hormetic effects of different insecticides on Spodoptera frugiperda (J.E. smith) (Lepidoptera: Noctuidae)

To protect crops from pest insects, farmers continuously use insecticides, which eventually degrade into residue due to abiotic or biotic factors. These residual effects of pesticides may cause low lethal and/or sublethal impacts on the exposed pest insect populations, leading to the induction of pest resurgence through hormesis and ultimately the development of resistance. Hormesis is a beneficial bi-phasic effect generally characterized by low-dose reproductive stimulation and high-dose inhibition. In the present study, we investigated the impact of low lethal and sublethal concentrations (LC₁₀, LC₂₀, and LC₃₀) of spinetoram, chlorantraniliprole, and thiodicarb on the F₀ generation as well as their multigenerational hormesis effects on the F₁ and F₂ generations of Fall Armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae). The study focused on reproductive parameters, fecundity, fertility, and life index parameters such as net reproductive rate (R₀), intrinsic rate of increase (r_m), finite rate of increase (λ), mean length of generation (T_c), and gross reproductive rate (GRR). Fecundity of S. frugiperda increased by 4.82%, 4.63% and 4.58%, while eggs fertility improved by 7.77%, 6.78% and 6.52% at LC₁₀ of thiodicarb, chlorantraniliprole and spinetoram, respectively, from the F₁ to F₂ generation. Further, interaction analysis (Concentration × Insecticidal treatments) revealed that important vital parameters like pre-oviposition period (POP), oviposition period (OP), post-oviposition period (PtOP), R_0, r_m, λ, T_c and GRR of F₀ were negatively impacted by LC₃₀ of all the tested insecticides and LC₂₀ of only spinetoram. However, LC₁₀ of any of the tested insecticides did not affect these parameters when compared with control. Furthermore, interactive analysis in multigenerational exposure experiments (Concentration × Insecticidal treatments × Generation(s)) showed hermetic effects of LC₁₀ of all tested insecticides which is more positive in F₂ as compared to F₁ generation. These unwanted positive hermetic effects of low lethal concentrations (LC₁₀) of tested insecticides in offspring of exposed parental population of S. frugiperda indicated its resistance and/or resurgence. Furthernore, present study emphasizes the necessity for additional research to elucidate the underlying mechanisms responsible for these effects.