Abstract

Detoxifying enzyme inhibitors are being used in insecticide formulations to restore insect susceptibility. Essential oils, also known as biopesticides, are volatile plant secondary metabolites. This study aimed to determine the potential of two essential oil constituents (thymol and (R)-(+)-pulegone) to act against the detoxifying enzymes of Spodoptera litura. Thymol and (R)-(+)-pulegone were studied on the third instar larvae of S. litura by topical application under laboratory conditions. Thymol and (R)-(+)-pulegone were found to be highly toxic to S. litura (24 h LC<inf>50</inf> values of ~5.61 and 8.35 μg/larva, respectively) and significantly decreased the activity of carboxylesterases and cytochromes P450. Moreover, thymol (1.79 and 3.51 μg/larva) and (R)-(+)-pulegone (2.56 and 5.15 μg/larva) had a significantly higher inhibitory effect on carboxylesterase activity than the commercial inhibitor triphenyl phosphate (16 μg/larva). The results indicated that thymol and (R)-(+)-pulegone have the potential to be used as alternative inhibitors to develop insecticide formulations for controlling the agricultural insect pest S. litura.