UTTAR PRADESH JOURNAL OF ZOOLOGY

Essential oils (EOs) are well known for their diverse insecticidal properties, including fumigant activity against insect pests infesting stored products. However, their effects on insect physiological processes may differ among oils. This study evaluated acetylcholinesterase (AChE) activity in adult C. maculatus following 24-h fumigation in desiccators using seven essential oils (Ajwain, Cumin, Coriander, Dill, Celery, Caraway and Black Pepper), at their respective lethal concentrations. The oils were extracted by the hydrodistillation method using a Clevenger apparatus. The LC₅₀ concentrations ranged from 18.8 to 154.8 µL L⁻¹, and observed mortality ranged from 45 to 55% (n = 20, r = 3), whereas mortality in the untreated control was 3.33%. The AChE activities were measured in surviving adults in three replicates using Ellman’s assay. A significant treatment effect was detected among the seven oils and the untreated control. Untreated insects showed the highest AChE activity (44.51 ± 0.96 U min⁻¹ mg⁻¹ protein), whereas Caraway-treated survivors exhibited the lowest activity (11.51 ± 1.18). Relative to the untreated control, AChE activity was reduced by 13.60–74.14% across the oil treatments, with the greatest reduction observed following Caraway exposure, followed by Celery (42%), Ajwain (38.2%), Black Pepper (36.9%) and Dill (30.9%). Cumin and Coriander produced comparatively lower reductions of 13.9 and 13.6%, respectively. These results demonstrate oil-specific alterations in AChE activity among surviving adults despite a similar mortality endpoint. The findings support the inclusion of biochemical endpoints alongside mortality for characterising the physiological effects of acute essential-oil fumigation and provide a basis for further concentration-, time- and mechanism-oriented investigations of neurophysiological responses in C. maculatus. This study provides an opportunity to identify promising essential oils for sustainable, non-synthetic approaches to managing bruchids infesting stored pulses.