Eco-friendly control of Helicoverpa armigera using synergistic mixtures of thymol and eucalyptol

The cotton bollworm, Helicoverpa armigera (Hübner), is a widely distributed, highly polyphagous lepidopteran pest that poses a major threat to agricultural productivity across various cropping systems. Successful management of this pest relies on continuous scientific investigation and targeted management strategies within Integrated Pest Management programs. This study investigated the insecticidal efficacy of pure thymol and 1,8-cineole (also known as Eucalyptol), both separately and in binary combination, against 3rd instar larvae of H. armigera. The bioassay findings revealed that thymol exhibited significantly greater toxicity than 1,8-cineole at both sublethal (LC₃₀ = 1.45% w/v) and lethal (LC₅₀ = 3.88% w/v) concentrations, whereas the corresponding values for 1,8-cineole were LC₃₀ = 2.77% w/v and LC₅₀ = 6.88% w/v. Binary mixtures of these compounds demonstrated enhanced toxicity compared to their individual applications, exhibiting both synergistic and additive interactions. In addition to mortality assessments, biochemical responses evaluated in larvae following exposure to individual compounds and their binary mixture at both lethal (LC₅₀) and sublethal (LC₃₀) concentrations. The binary mixture significantly inhibited key detoxification enzymes including general esterases, glutathione S-transferase, and cytochrome P450 compared to single compound exposures. Conversely, there was marked induction of antioxidant defense enzymes (catalase, peroxidase, and superoxide dismutase). The synergistic combination also exhibited significant inhibitory effects on both acetylcholinesterase and Na⁺/K⁺-ATPase enzymatic activities. According to our findings, combined formulations of thymol + 1,8-cineole represent a promising eco-friendly alternative for the management of H. armigera. Such formulations could contribute to resistance management strategies while reducing reliance on conventional chemical pesticides.