Ecotoxicological Impact of Ad-Hoc Approved Synthetic Insecticides on the Biological Performance of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae)

Abstract

Laboratory assessments were conducted to evaluate the efficacy of seven ad-hoc approved insecticides, namely Chlorantraniliprole, Emamectin benzoate, Spinetoram, Thiodicarb, Chlorantraniliprole + Lambda-cyhalothrin, Emamectin benzoate + Lufenuron, and Novaluron + Emamectin benzoate, against Spodoptera frugiperda. These evaluations were carried out using a diet incorporation assay in a controlled laboratory environment with a temperature of 27 ± 1°C, relative humidity of 65 ± 5%, and a 12:12 (L:D) photoperiod. During the bioassay procedure, it is noteworthy that the doses of all tested insecticides were carefully administered within the minimum range of their recommended field rates. In acute toxicity trials, spinetoram had the greatest impact on reducing the survival of S. frugiperda. Similarly, corrected mortality was highest with spinetoram and lowest with thiodicarb. Additionally, chronic toxicity trials were conducted using life table response experiments (LTREs) in the F1 progeny of the group that had experienced acute toxicity. Extended development with the highest mortality was observed in spinetoram compared to other tested insecticides. Furthermore, life indices parameters like potential fecundity (Pf), natality rate (mx), intrinsic rate of increase (rm), net reproductive rate (mx) and finite rate of increase (λ) was greatly reduced in S. frugiperda treated with spinetoram compared with other insecticides specially thiodicarb. However, mean generation time (Tc), corrected generation time (τ) and the doubling time (DT) was prolonged in spinetoram compared with other tested insecticides. Furthermore, in sex ratio analysis, all tested insecticides, except for thiodicarb, led to a significant decrease in the proportion of females in the population of S. frugiperda. These findings strongly suggest the possible emergence of resistance in S. frugiperda against thiodicarb. Moreover, considering the endorsement of this insecticide by the Government of India through ad-hoc approval, farmers are likely to persist in its application. Hence, it is imperative to conduct further validation of these results, necessitating field evaluations for confirmation.