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written by: Ben Gregory and Minh Le Vampires do exist – they’re just tiny and have six legs. Blood-feeding insects, such as mosquitoes, feed on the blood of other animals to complete their life cycle. Blood provides many essential nutrients that aren’t easy to get elsewhere in nature. Unfortunately for us, blood-feeding insects can carry pathogens that cause human diseases, like malaria, West Nile, and Zika. For this reason, many scientists are interested in learning how the process of blood feeding works, and what we might be able to do to keep ourselves safe from it. One of these scientists, Dr. Chloé Lahondère of the Department of Biochemistry at Virginia Tech, has spent years learning about one unusual element of blood-feeding that you probably haven’t considered: how to stay cool. Your blood is hot – about 100°F in your body! Given that insects are cold-blooded animals and must maintain their body temperature below a certain level, the question arises “how does a blood-feeder feed on piping hot blood without overheating? Dr. Lahondère is using the kissing bug (Figure 1, Left) to answer this question. The kissing bug is a species of true bug (insects with a syringe-like mouthpart) that are found throughout the American continent. They are a vector of the protozoan parasite Trypanosoma cruzi, which causes Chagas disease. Around 50% of kissing bugs are infected with this parasite. They transmit Chagas disease to humans and pets via infected feces that come into contact with the blood-feeding wound. So, how does a kissing bug keep cool when drinking blood at temperatures of 100°F and higher? Dr. Lahondère and her team took a thermal image of a kissing bug feeding (Figure 1). This allowed them to see how quickly the blood dropped in temperature as the insect sucked it through the head, thorax, and finally into its abdomen, where the blood was cooled to just above room temperature (Figure 1). These observations allowed them to see that the blood was cooled as it passed through the head.
They decided to take a closer look. They hypothesized that the blood could be falling in temperature so quickly because kissing bugs have a form of countercurrent heat exchanger in their heads. Countercurrent heat exchange is found in many animal species including birds, whales and other insects such as bumblebees. It occurs when a hot fluid moving in one direction transfers its heat to a cooler fluid moving in the opposite direction. The amount of heat exchanged when hot and cold fluids flow in the opposite direction is a very efficient way to rapidly lower the temperature of a hot blood-meal. The insect equivalent of blood is called haemolymph. Haemolymph doesn’t flow through veins like our blood but bathes most tissues directly and circulates throughout the body from the back to the front via a current created by a long, tubular heart and aorta. Interestingly, contrary to most other insects, the kissing bug heart is located at the very tip of their abdomen. This means that the haemolymph is at its coolest when it enters the heart, after which it is pumped towards the head. By dissecting kissing bug heads, Dr. Lahondère and her team found that the cooler haemolymph circulating in the aorta is in direct contact with the esophagus, where the hot blood-meal is flowing into the bug in the opposite direction. They demonstrated the effectiveness of this cooling system by cutting the kissing bug’s heart (dorsal vessel) and preventing the flow of cool haemolymph toward the head. This prevented the ingested blood from cooling down (Figure 2).  Figure 2. Temperature throughout a kissing bug’s body when dorsal vessel is intact (Left) and severed (Right) It is interesting to see how evolution shaped the circulatory system of this animal; finding an elegant solution to the problems posed by relying on hot food for survival. As Dr. Lahondère and her team continue to investigate kissing bugs, we continue to learn more about the mechanisms they use to survive and bite us. Though they are our enemies, you must know thy enemy. To learn more about Dr. Lahondère’s research, you can visit her website.
Author Bios: Ben Gregory (he/him) is a PhD student in the Fritz lab at the University of Maryland investigating how urbanization shapes the evolution of mosquitoes. Minh Le is a 3rd year Entomology PhD student in the Pick Lab at the University of Maryland. His research interest is in how transcription factors evolution shapes insect segmentation diversity. Citations: Images courtesy of Dr. Chloé Lahondère Chloé Lahondère, Teresita C Insausti, Rafaela MM Paim, Xiaojie Luan, George Belev, Marcos H Pereira, Juan P Ianowski, Claudio R Lazzari (2017) Countercurrent heat exchange and thermoregulation during blood-feeding in kissing bugs eLife 6:e26107 https://doi.org/10.7554/eLife.26107 Comments are closed.
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