Comparative study on the behavioral response and acute toxicity of some essential oil compounds and their binary mixtures to larvae of Helicoverpa armigera, Spodoptera litura and Chilo partellus

- Acute toxicity and behavioral response of five essential oil compounds against 3 lepidoperan species have been compared.
- Thymol was a generalist toxicant with toxic, feeding deterrence, ovicidal and the oviposition inhibitory effects.
- H. armigera and S. litura gustatory responses were almost similar as compared to C. partellus, a maize borer with positive phototropism.
- Oviposition preference was independent of toxic action.
- Thymol and linalool were synergistically toxic against all the 3 species.

Comparative bioefficacy of five compounds in terms of acute toxicity and feeding and oviposition deterrence was determined against Helicoverpa armigera (Hübner), Spodoptera litura (F.) and Chilo partellus Swinhoe. Thymol was universally the most active compound, though with variable LD50 values depending upon the species evaluated. S. litura was the most susceptible with an LD50 of 28.5 μg/larva followed by C. partellus with an LD50 of 189.7 μg/larva and H. armigera with an LD50 = 290.8 μg/larva. Comparative trend of acute toxicity, however, showed a significant overlap in activity for C. partellus and H. armigera when treated with various compounds. There was a reverse trend for feeding deterrence where H. armigera and S. litura gustatory response was similar in comparison to C. partellus, a specific maize borer that exhibits positive phototropism. Thymol and linalool were synergistically toxic against all the 3 species and carvacrol was antagonistic in all combinations. Response of S. litura was definitely different compared to the other 2 species. All the compounds deterred oviposition and were ovicidal too. Overall, thymol was the most active compound as an acute toxicant, oviposition deterrent, ovicide or a feeding deterrent against all the three insects. Other than thymol, 1,8-cineole and linalool were effective ovicidal compounds with an LC50 = 4.0 and 3.3 mg/ml, respectively against H. armigera eggs but less active as oviposition deterrents than thymol; however, this deterrence was similar to the one observed in S. litura moths. 1,8-cineole and linalool were similar in deterring oviposition of C. partellus moths. Anethole was the least active as oviposition deterrent against all the 3 species evaluated and ODI50 values were 2.5-5-fold higher for this compound in both choice and no-choice situation.