Blood as fuel: the metabolic cost of pedestrian locomotion in Rhodnius prolixus.

Active searching for vertebrate blood is a necessary activity for haematophagous insects, and it can be assumed that this search should also be costly in terms of energetic expenditure. Whether by swimming, walking, running or flying, active movement requires energy, increasing metabolic rate relative to resting situations. We analysed the respiratory pattern and energetic cost of pedestrian locomotion in the blood-sucking bug Rhodnius prolixus using flow-through respirometry, by measuring carbon dioxide emission and water loss before, during and after walking. We observed an increase in the metabolic rate during walking as compared with resting of up to 1.7-fold in male R. prolixus and 1.5-fold in females, as well as a change in their respiratory pattern, which switched from cyclic during rest to continuous when the insects started to walk, remaining in this condition during locomotion and for several minutes after stopping. Walking induced a significant loss of mass in both males and females. This can be explained by an increase in both metabolic rate and water loss during walking. These data constitute the first metabolic measures of active haematophagous insects and provide the first insights into the energetic expenditure associated with the active search for blood in this group.

Functional evaluation of Heat Shock Proteins 70 (HSP70/HSC70) on Rhodnius prolixus (Hemiptera, Reduviidae) physiological responses associated with feeding and starvation.

Blood-sucking vectors must overcome thermal stress caused by intake of proportionally large amounts of warm blood from their hosts. In response to this, Heat Shock Proteins (HSPs) such as the widely studied HSP70 family (the inducible HSP70 and the cognate form HSC70, known for their role in preserving essential cellular functions) are rapidly up-regulated in their tissues. The triatomine Rhodnius prolixus is an important vector of Trypanosoma cruzi, the causative pathogen of Chagas' disease, and is also a model organism for studying insect biology and physiology. In this work, we observed that the expression of Rhodnius prolixus HSP70 was rapidly up-regulated in response to thermal shocks (0 °C and 40 °C) and also during the first hours after feeding on blood. HSP70/HSC70 RNAi knockdown elicited important alterations in R. prolixus physiological responses triggered by blood meal and starvation. HSP70/HSC70 knockdown insects showed lower resistance to prolonged starvation in comparison to appropriate controls, dying between 32 and 40 days after dsRNA injection. After blood feeding, the physiological effects of HSP70/HSC70 knockdown were more prominent and the insects died even earlier, within 14-20 days after feeding (21-27 days after dsRNA injection). These bugs showed impaired blood processing and digestion, reduced energetic metabolism and the midgut immune responses were compromised. Our findings suggest that HSP70/HSC70 depletion affected R. prolixus in starvation or fed conditions. After feeding, the arrival of blood in the digestive tract of knockdown insects fails to activate essential signaling pathways involved in blood processing, producing several alterations in their physiological processes enough to generate a premature death.

Haematophagy is costly: respiratory patterns and metabolism during feeding in Rhodnius prolixus.

Feeding on the blood of vertebrates is a risky task for haematophagous insects and it can be reasonably assumed that it should also be costly in terms of energetic expenditure. Blood circulates inside vessels and it must be pumped through narrow tubular stylets to be ingested. We analysed the respiratory pattern and the energetic cost of taking a blood meal in Rhodnius prolixus using flow-through and stop-flow respirometry to measure carbon dioxide emission, oxygen consumption and water loss before and during feeding. We observed an increase of up to 17-fold in the metabolic rate during feeding and a change in the respiratory pattern, which switched from a discontinuous cyclic pattern during resting to a continuous pattern when the insects started to feed, remaining in this condition unchanged for several hours. The energetic cost of taking a meal was significantly higher when bugs fed on a living host, compared with feeding on an artificial feeder. No differences were observed between feeding on blood or on saline solution in vitro, revealing that the substrate for feeding (vessels versus membrane) and not the nature of the fluid was responsible for such a difference in the energetic cost. Water loss significantly increased during feeding, but did not vary with feeding method or type of food. The mean respiratory quotient in resting bugs was 0.83, decreasing during feeding to 0.52. These data constitute the first metabolic measures of an insect during blood feeding and provide the first insights into the energetic expenditure associated with haematophagy.