Mode of action of the essential oil from Cymbopogon giganteus Chiov. in two species of Callosobruchus: C. maculatus F. and C. subinnotatus Pic. (Coleoptera: Chrysomelidae: Bruchinae)

This study was designed to investigate the insecticide potential of the essential oil of Cymbopogon giganteus on two sympatric Bambarra groundnuts depredators, Callosobruchus maculatus and C. subinnotatus, and the physiological alterations induced in the individuals. At physiological level, the modulations of a neural enzyme (acetylcholinesterase) and metabolic enzymes involved in detoxication and defense against oxidants (glutathione-S-transferase, superoxide dismutase, glutathione reductase and catalase  were monitored in adults of both Callosobruchus species exposed to EO by fumigation. Treatment of adults with the EO did not elicit significant effects on AChE activity in vitro on untreated adults as in vivo on knock down adults, did not show any significant variation in both species. However, this oil provokes an increasing of 33.35% of GST specific activity in C. maculatus, but, a decrease of 25.84% in C. subinnotatus. Superoxide Dismutase specific activity of C. maculatus did not show significant variations in presence of this EO which induced however, an increase of 346.53% of C. subinnotatus’ SOD. This essential oil induced also an increase of Glutathione Reductase (GR) and Catalase (CAT) in both species. The highest increasing of GR was observed in C. maculatus with 157.86% and 52.51% in C. subinnotatus; while for CAT, these augmentations were 18.21% and 25% respectively on C. maculatus and C. subinnotatus.
These different effects of this EO on detoxification and oxidative enzymes show that it has a pro oxidant effect on these pests inducing probably insects’ death by lipid per oxidation, protein and DNA oxidations.