Bioactivity of a new insect repellent: laboratory evaluation against Sitophilus oryzae = Bioattività di un nuovo repellente per insetti: valutazione in laboratorio nei confronti di Sitophilus oryzae

Essential oils (EOs) have been often proposed as a valid alternative to synthetic pesticides to control stored grain pests. Generally, EOs contain various percentages of cyclic monoterpenes such as menthol, menthone, carvone, and also phenolic derivatives as eugenol with repellent properties. This study aims to evaluate the repellence of 22 main constituents of various EOs through preliminary tests with the “Area Preference” method against Sitophilus oryzae (Coleoptera: Curculionidae), one of the main pests of stored products, that causes important economic losses to cereals and their derivatives. Among the substances tested, eugenol (C10H12O2) showed the greatest repellent activity. However, eugenol is poorly suitable for use in stored grains due to its low persistence and strong and spicy odour. In this research, we modified the eugenol structure to obtain a new compound (compound A, C18H20O4) with a higher molecular weight (less volatile and odorous but more persistent) but with still high bioactivity. The bioactivities of compound A and eugenol were tested in a two-way static olfactometer. Compound A showed a greater repellence and persistence than eugenol against S. oryzae. Compound A was subsequently evaluated by sensory analysis (Panel Tests) in comparison with eugenol. The results of the Panel Test indicate that compound A is significantly less odorous than eugenol. We can therefore conclude that: i) the modification of the eugenol structure increases both the effectiveness and the duration of the repellent activity; ii) the reduction of the volatility can significantly reduce the strong smell, increasing the compatibility of the compound with food. Overall, the repellency of compound A, its persistence and lower smell intensity indicate that it could represent a valid alternative to other synthetic repellents in food active packaging for the control of foodstuffs insects.