Activity and shelter-related behavior in Rhodnius prolixus: The role of host odours

Triatomine bugs are considered nocturnal insects that feed on the blood of vertebrates and remain hidden inside narrow shelters during daylight hours. Nevertheless, it is not clear whether these insects become active and leave their shelters on a daily basis, less frequently or, even fortnightly. Activity patterns were studied in Rhodnius prolixus Stål, 1859 (Hemiptera: Triatominae) associated with shelters to evaluate whether the decision to leave a shelter depends on bug starvation and the presence of host odours. Experiments were conducted with groups of 5th instar nymphs released in an experimental arena offering an artificial shelter consisting of a piece of corrugated cardboard positioned in its centre. Results indicate that host odours promoted a significant increase in shelter related activity, i.e. shelter-leaving or entering movements, and also in bug locomotion. This increase could only be observed with bugs starved for 30 or 60 days, but not for 21 days. Most R. prolixus nymphs that left shelters and engaged in locomotory activity were starved and in the presence of host odours. Even though R. prolixus is mostly considered a very active and "aggressive" triatomine, our results contradict this perspective and suggest that its main strategy regarding hosts is to wait and carefully evaluate feeding chances before becoming exposed. This behavioural strategy might have arisen through their evolution in palm trees in association with a diverse fauna that may impose predation risks.