Effects of starvation on the olfactory responses of the blood-sucking bug Rhodnius prolixus

Blood-sucking insects use olfactory cues in a variety of behavioral contexts, including host-seeking and aggregation. In triatomines, which are obligated blood-feeders, it has been shown that the response to CO2, a host-associated olfactory cue used almost universally by blood-sucking insects, is modulated by hunger. Host-finding is a particularly dangerous task for these insects, as their hosts are also their potential predators. Here we investigated whether olfactory responses to host-derived volatiles other than CO2 (nonanal, alpha-pinene and (-)-limonene), attractive odorant mixtures (yeast volatiles), and aggregation pheromones (present in feces) are also modulated by starvation in the blood-sucking bug Rhodnius prolixus. For this, the responses of both non-starved and starved insects were individually tested at the beginning of the scotophase using a dual-choice "T-shaped" olfactometer, in which one of its arms presented odor-laden air and the other arm presented odorless air. We found that the response of non-starved insects toward host-odorants and odorant mixtures was odor-dependent: insects preferred the odor-laden arm of the maze when tested with alpha-pinene, the odorless arm of the maze when tested with (-)-limonene, and distributed at random when tested with yeast volatiles or nonanal. In contrast, starved insects significantly preferred the odor-laden arm of the maze when tested with host-odorants or yeast volatiles. When tested with aggregation be, while starved insects preferred the odorless arm of the maze; insects that were even more starved (8-9 weeks post-ecdysis) significantly preferred the odor-laden arm of the maze. We postulate that this odor- and starvation-dependent modulation of sensory responses has a high adaptive value, as it minimizes the costs and risks associated with the associated behaviors. The possible physiological mechanisms underlying these modulatory effects are discussed. (C) 2013 Elsevier Ltd. All rights reserved.