Countercurrent heat exchange and thermoregulation during blood-feeding in kissing bugs

Abstract

Blood-sucking insects experience thermal stress at each feeding event on endothermic vertebrates. We used thermography to examine how kissing-bugs Rhodnius prolixus actively protect themselves from overheating. During feeding, these bugs sequester and dissipate the excess heat in their heads while maintaining an abdominal temperature close to ambient. We employed a functional-morphological approach, combining histology, µCT and X-ray-synchrotron imaging to shed light on the way these insects manage the flow of heat across their bodies. The close alignment of the circulatory and ingestion systems, as well as other morphological characteristics, support the existence of a countercurrent heat exchanger in the head of R. prolixus, which decreases the temperature of the ingested blood before it reaches the abdomen. This kind of system has never been described before in the head of an insect. For the first time, we show that countercurrent heat exchange is associated to thermoregulation during blood-feeding.

eLife digest

Many insect species have adopted the blood of birds and mammals as their main or even only food. Yet, blood is not freely available in nature, but it circulates inside vessels hidden under the skin of animals much bigger than the insect and capable of defending themselves from getting bitten. To succeed in getting a meal, blood-sucking insects must be able to feed quickly and take in as much blood as possible. Each time that they do this, a huge amount of warm fluid enters their body in just a few minutes. The blood temperature can be up to 20° or 25°C warmer than the insect itself. Moreover, an insect called a kissing bug may ingest up to 10 times its own weight in only fifteen minutes. The consequence is overheating and potentially harmful thermal stress.

Kissing bugs do not seem to suffer any harmful consequence of taking massive meals from warm-blooded animals. But why? The answer was unexpected: they simply do not warm up when they take a blood meal. However, it was not known how they manage to cool down the ingested blood.

By combining classical methods of studying anatomy with state of the art technologies, Lahondère et al. discovered that kissing bugs possess a sophisticated heat exchanger inside their heads. It works by transferring the heat associated with the ingested blood to the haemolymph (insect blood); these fluids circulate in opposite directions inside ducts that are close to each other in the head.

The discovery of a new system used by insects to cope with thermal stress expands our knowledge of insect physiology and opens new lines of research. The kissing bug heat exchanger could also serve as inspiration for equivalent technological systems. Last but not least, kissing bugs spread the parasites that cause Chagas disease in the Americas. Finding ways to disrupt the heat exchanger could prevent kissing bugs from feeding on blood, and so help to control the spread of disease.