Effect of formulated essential oil of Ajwain, Trachyspermum ammi (L.) on some biological and physiological parameters of cotton bollworm, Helicoverpa armigera

Unrestricted use of chemical insecticides, especially at high concentrations, has reduced their efficacy. Plant-based pesticides, due to their relatively high safety levels to humans and environment as well as effective control on insects, have become a suitable alternative to conventional pesticides. The aim of this study was to investigate the biological and physiological effects of the formulated essential oil of Trachyspermum ammi (L.) on the larvae of Helicoverpa armigera Hüb. The obtained essential oil was formulated into an emulsion using Tween 20 as emulsifier. Chemical analysis of the extracted essential oil indicated that Terpinen (14.4%), Cymene (18.5%), and Thymol (61.6%) were the major compounds. The essential oil of T. ammi have a significant repellency rate on third and sixth instar larvae of cotton bollworm at different observed time intervals, with an average repellency rate of 61-76%. Regarding fumigant toxicity, the highest concentration of the essential oil (500 µL/L) resulted in 100% larval mortality. The LC50 value for fumigant toxicity measured as 82.73 µL/L. The duration of larval development significantly increased in treatments compared to control. In EO concentrations of 2.5-1.25 percent an increase was observed respectively in the duration of the larval stage by 9 and 7 days. The pupae and adult’s emergence affected in dose dependent manner. At concentration of 50 µl/l, 89% inhibition of protease enzyme recorded. With regards to the biological and physiological effects observed in the formulated T. ammi essential oil, with complimentary researches, it could be used in integrated management programs of cotton bollworm.