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Spodoptera litura (Fabricius) is a major polyphagous pest of global relevance due to the damage it causes to various crops. Chlorpyrifos (CPF) is generally used by farmers to manage S. litura, however, its widespread use has resulted in the development of insecticide resistance. Therefore, in the present study, a population of S. litura was exposed to CPF for eight generations under laboratory conditions, resulting in a 2.81-fold resistance ratio compared with that of the unselected laboratory population (Unsel-Lab). The exposure of Unsel-Lab and CPF-Sel populations to their respective lethal and sublethal concentrations reduced larval survival, adult emergence, and prolonged development period, and induced morphological deformities in adults. The reproductive and demographic parameters were also significantly lowered in the treated larvae of both populations at higher concentrations. Moreover, hormetic effects on fecundity, next-generation larvae, the net reproductive rate (R 0 ), and relative fitness (R f ) were observed at lower sublethal concentrations of CPF, specifically at the LC 5 of Unsel-Lab and the LC 10 of the CPF-Sel population. Sublethal exposure to CPF negatively affected the biological and demographic parameters in both populations, although the impact was more prominent in the CPF-Sel population. The relative fitness of the CPF-Sel was also greatly reduced at the LC 50 (0.28) compared to that of the Unsel-Lab population. However, only a marginal trade-off of insecticide resistance evolution was observed in the CPF-Sel population in the absence of insecticide selection pressure. These results provide useful information for devising improved pest management strategies for CPF resistance in S. litura., Competing Interests: Declarations. Ethical approval: This article does not contain any studies involving humans/animals/plants that need approval from an ethical committee. Competing interests: The authors declare no competing interests., (© 2024. The Author(s).)

The imprudent use of insecticides causes the development of resistance in insect pest populations, contamination of the environment, biological imbalance and human intoxication. The use of microbial pathogens combined with insecticides has been proposed as an alternative strategy for insect pest management. This IPM approach may offer effective ways to control pests, in addition to lowering the risk of chemical residues in the environment. Spodoptera litura (Fabricius) is a major pest of many crops like cotton, maize, tobacco, cauliflower, cabbage, and fodder crops globally. Here, we evaluated the combined effects of new chemistry insecticides (chlorantraniliprole and emamectin benzoate) and entomopathogenic bacterial strains, Shewanella sp. (SS4), Thauera sp. (M9) and Pseudomonas sp. (EN4) against S. litura larvae inducing additive and synergistic interactions under laboratory conditions. Both insecticides produced higher larval mortality when applied in combination with bacterial isolates having maximum mortality of 98 and 96% with LC 50 of chlorantraniliprole and emamectin benzoate in combination with LC 50 of Pseudomonas sp. (EN4) respectively. The lower concentration (LC 20 ) of both insecticides also induced synergism when combined with the above bacterial isolates providing a valuable approach for the management of insect pests. The genotoxic effect of both the insecticides was also evaluated by conducting comet assays. The insecticide treatments induced significant DNA damage in larval hemocytes that further increased in combination treatments. Our results indicated that combined treatments could be a successful approach for managing S. litura while reducing the inappropriate overuse of insecticides., (© 2023. Springer Nature Limited.)

Background: Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) also known as tobacco caterpillar, is one of the most serious polyphagous pests that cause economic losses to a variety of commercially important agricultural crops. Over the past few years, many conventional insecticides have been used to control this pest. However, the indiscriminate use of these chemicals has led to development of insecticide resistant populations of S. litura in addition to harmful effects on environment. Due to these ill effects, the emphasis is being laid on alternative eco-friendly control measures. Microbial control is one of the important components of integrated pest management. Thus, in search for novel biocontrol agents, the current work was carried out with the aim to evaluate the insecticidal potential of soil bacteria against S. litura., Results: Among the tested soil bacterial isolates (EN1, EN2, AA5, EN4 and R1), maximum mortality (74%) was exhibited by Pseudomonas sp. (EN4). The larval mortality rate increased in a dose-dependent manner. Bacterial infection also significantly delayed the larval development, reduced adult emergence, and induced morphological deformities in adults of S. litura. Adverse effects were also detected on various nutritional parameters. The infected larvae showed a significant decrease in relative growth and consumption rate as well as efficiency of conversion of ingested and digested food to biomass. Histopathological studies indicated damage to the midgut epithelial layer of larvae due to the consumption of bacteria treated diet. The infected larvae also showed a significantly decreased level of various digestive enzymes. Furthermore, exposure to Pseudomonas sp. also caused DNA damage in the hemocytes of S. litura larvae., Conclusion: Adverse effects of Pseudomonas sp. EN4 on various biological parameters of S. litura indicate that this soil bacterial strain may be used as an effective biocontrol agent against insect pests., (© 2023. The Author(s).)