Lamiaceae species are well-known in traditional medicine. In the last years, Essential Oils (EOs) of
many Lamiaceae have showed to be excellent repellents and/or insecticides. Tropical Andes are
extremely rich in endemic flora, possible source of new bioactive substances. Here, we verified the
insect repellent activity of the EOs extracted from Clinopodium tomentosum and C. nubigenum,
two Lamiaceae typical of the Ecuadorian Andes. The two EOs were tested against the maize weevil
Sitophilus zeamais (Motschulsky) (Coleoptera: Curculionidae), one of the most destructive pests of
stored and processed cereals. To characterize the olfactory sensilla of S. zeamais, its antennal
structure was investigated by scanning and transmission electron microscopy. The
electrophysiological and behavioural responses of the insect to the EOs were then investigated by
electroantennography and olfactometer trials. The morphological study revealed the presence of
three types of sensilla (Basiconic Sensillum 1, 2, and Grooved Peg Sensillum), that could be
involved in the perception of the EOs volatile compounds. Accordingly, the electroantennography
showed a positive dose-dependent response of the insect antennae to both the EOs. The
behavioural tests displayed a significative repellence of the EOs, starting from 8.4 μL L-1 air, and
that the efficacy and readiness of the response to the stimulus was higher for C. tomentosum. In
conclusion, both the EOs are detected by the insect by its antennae and exert a strong repellent
effect. The results confirm that Andean flora represents a valuable source of unexploited bioactive
substances that can be utilized as promising tools for foodstuff pests’ control
