Abstract

Background: The tobacco armyworm Spodoptera litura (Lepidoptera: Noctuidae) is a notorious insect pest of crops. Tobacco armyworm (Spodoptera litura) is a destructive insect pest of crops that has acquired broad spectrum resistance to conventional chemical insecticides. Entomopathogenic fungi (EPF) are widely acknowledged as environmentally friendly biological control agents and have enormous potential in integrated pest management (IPM) programs. However, their use is restricted because they are slower in infecting and killing insects than chemical insecticides. The molting hormone of insects, ecdysone, controls the development of larvae, and during molting, it can cause a temporary rise in physiological vulnerability because of the loss of integrity of the cuticle and changes in immune activity. Objective: The entomopathogenic fungi, Metarhizium anisopliae (M. anisopliae) and Paecilomyces javanicus (P. javanicus), were used in this study to determine their pathogenicity against third-instar larvae of Spodoptera litura (S. litura) when present in an exogenously supplemented fungal supplement. Methods: Third-instar larvae were exposed to sublethal doses of 20-hydroxyecdysone, fungal suspension and 20-hydroxyecdysone and fungal suspension. Seven days of Larval mortality and developmental responses took place in a controlled laboratory setting. The interaction between treatments was evaluated using ANOVA. Results: Exogenous ecdysone significantly affected molting dynamics and increased larval susceptibility to fungal infection. The highest larval mortality (92% on day 7) was obtained when the larvae were fed both ecdysone and M. anisopliae, which was significantly higher than that of the fungal treatment alone. A synergistic effect was observed with the combination of ecdysone and P. javanicus, but the overall mortality was slightly lower. The results obtained indicate that physiological changes during molting induced by ecdysone promote the penetration and infection efficiency of the fungus. Conclusion: Exogenous ecdysone exposure in the pre-larval stage of S. litura significantly enhances its susceptibility to entomopathogenic fungi. This hormone-based approach could enhance the effectiveness of fungal biological control products and mitigate the delay in the action of EPF in IPM applications.