An antagonist of the neurotransmitter tyramine inhibits the hyperactivating effect of eugenol in the blood-sucking bug, Triatoma infestans

Eugenol is a botanical monoterpene found in the essential oils of several aromatic plants. It has shown to have insecticidal activity, modify insect behavior, and its site of action is most probably in the octopaminergic system. The aim of the present study was to explore whether tyramine receptors are involved in the hyperactivity produced by eugenol in Triatoma infestans, one of the main vectors of Chagas disease. Topical application of tyramine and eugenol increased locomotor activity in third instar nymphs of T. infestans in a dose-dependent way. Yohimbine hydrochloride, a tyramine antagonist, did not modify nymph activity. However, nymphs pretreated with yohimbine and then with tyramine or eugenol showed the same locomotor activity as the controls. Therefore, yohimbine hydrochloride inhibited the hyperactivating effect of both tyramine and eugenol. These results suggest that tyramine receptors are involved in the effect of eugenol on the locomotor activity of T. infestans.