Effects of menthol on nutritional physiology and enzyme activities of the lesser grain borer, Rhyzopertha dominica (F. 1792) (Coleoptera: Bostrichidae)

This present study aims to evaluate the insecticidal activity of a bioactive molecule, menthol, against a pest species, Rhyzopertha dominica (F. 1792) (Coleoptera: Bostrichidae). Effects were examined on mortality, enzymes of intermediary metabolism (ALP, GOT and GPT), nutritional reserves, digestive enzymes, and oxidative stress biomarker. Toxicological tests revealed the insecticide activity of this treatment with a dose-response relationship. In addition, ingestion (LC50 at 24 h: 0.69 mu l/ml) is the most effective mode of application compared to fumigation (LC50 at 24 h: 302 mu l/L air). The obtained results revealed an increase in the percent repellency as a function of concentrations. Moreover, the biochemical study shows that the treatment decreases the protein content and the energy reserves. In addition, it disrupts the activity of enzymes of intermediary metabolism (ALP, GOT and GPT) in R. dominica adult. Finally, menthol also disrupts the digestive enzymes activity in treated adults compared to controls. Indeed, the treatment reduces the specific activity of alpha-amylase, protease, chitinase, and lipase.