Mosquitoes stop biting because of cells in their rectum, not their brain

The receptor that tells a mosquito she is full lives in her rectum. Not her brain, where researchers expected to find it. Not in her midgut, where blood is digested. In her rectum - a tissue that, as Columbia University biologist Laura Duvall dryly noted, has been about as heavily studied as you might imagine.

The finding, published March 20 in Current Biology, redraws the map of how mosquito feeding behavior is regulated and adds to a growing body of evidence that the gut plays a far more active role in controlling appetite and behavior across species than scientists once appreciated.

From a blood meal to a three-day fast

Female mosquitoes - the ones that bite - undergo a dramatic behavioral shift after feeding on blood. For several days, they lose interest in humans entirely. They digest the blood, convert its protein into yolk, and deposit it in their eggs. During this window, they will not bite again even if a warm-blooded host is right in front of them.

How that behavioral switch works has been a puzzle. In earlier work as a postdoc, Duvall identified a receptor called Neuropeptide Y-like Receptor 7 (NPYLR7) as a key player. When NPYLR7 is destroyed, mosquitoes never feel full. They continue seeking blood meals even after feeding. The receptor is clearly essential for the appetite-suppressing signal that follows a blood meal.

The logical next step was to find where NPYLR7 sits in the body. Duvall's team hypothesized it would be distributed across multiple tissues, with the brain as the most likely command center. In most animals, appetite-regulating receptors are concentrated in the central nervous system. That is where the behavioral decisions happen.

But NPYLR7 was not in the brain. It was in the rectum.

Rectal cells that behave like neurons

To understand how rectal cells communicate with the nervous system, Duvall's team used a fluorescent calcium indicator - a protein that glows when calcium levels rise, a hallmark of cellular signaling. After mosquitoes feed, nearby nerve cells release a peptide called RYamide that activates NPYLR7. The team showed that applying this peptide triggered calcium surges in the rectal cells, similar to the response seen in neurons.

But the communication was not one-directional. After NPYLR7 activation, the rectal cells showed changes suggesting they were releasing signaling packets back to the nervous system. In other words, these gut cells were not passive recipients of neural commands. They were having a conversation with the brain - sensing nutritional status and reporting it back.

The rectal cells were almost behaving like neurons themselves - sensing, signaling, and participating in a feedback loop that controls behavior. Their position in the rectum may be strategic: sitting at the end of the digestive tract, they are ideally placed to monitor what nutrients are available and how full the mosquito is, then relay that information to the central nervous system.

An echo of GLP-1 in a different species

Duvall drew a direct parallel to the biology behind GLP-1 receptor agonists - the class of drugs that includes semaglutide and tirzepatide, now widely used for weight loss and diabetes management in humans. GLP-1 (glucagon-like peptide-1) is released by cells in the human gut and plays a central role in signaling fullness to the brain.

The parallel is not superficial. In both mosquitoes and humans, peptides produced in the gut communicate with the nervous system to regulate feeding behavior. The specific molecules differ, but the architecture is strikingly similar: gut-derived signals that suppress appetite by talking to the brain.

This convergence across species separated by hundreds of millions of years of evolution suggests that gut-brain signaling as a mechanism for appetite control is deeply conserved. The gut is not merely a processing organ. It is a sensory organ - one that monitors internal state and shapes behavior accordingly.

A more accessible target for mosquito control

The finding also has practical implications for vector control. Mosquitoes transmit malaria, dengue, Zika, and a roster of other diseases that collectively kill hundreds of thousands of people each year. Disrupting their feeding behavior - making them unable to sense fullness, or making them permanently uninterested in blood - could reduce disease transmission.

A receptor in the brain is a difficult target. Getting a compound past the blood-brain barrier is a challenge even in human pharmacology, let alone in an insect. But a receptor in the rectum is far more accessible. Duvall pointed out that you could potentially feed mosquitoes a compound that disrupts NPYLR7 function - delivered through a sugar bait, for instance - without needing it to reach the brain.

If NPYLR7 activation suppresses biting, a drug that mimics or enhances that signal could keep mosquitoes in their post-feeding, non-biting state for longer. Conversely, disrupting the receptor could prevent them from ever feeling full, which might seem counterproductive but could be useful in trapping strategies where mosquitoes that never stop seeking bait are more easily captured.

Neither approach is ready for deployment. The receptor biology needs further characterization, candidate compounds need identification and testing, and any intervention would need to demonstrate specificity - disrupting mosquito feeding without harming other insects or the broader ecosystem.

What remains unknown

The study establishes that NPYLR7 is located in the rectum and that rectal cells communicate bidirectionally with the nervous system. But the precise mechanism by which rectal cell signaling translates into behavioral change - the steps between a calcium surge in the gut and a mosquito deciding not to bite - remains unclear.

The study was conducted in Aedes aegypti, the yellow fever mosquito and primary vector for dengue and Zika. Whether the same receptor localization and signaling pathway operate in other disease-carrying species, such as Anopheles mosquitoes that transmit malaria, has not been tested.

The broader claim that gut signaling is more important for behavior than previously appreciated, while supported by this work and by GLP-1 research in humans, is still being defined in its scope. How many behaviors are influenced by gut-derived signals? How does gut signaling interact with other regulatory systems? These are active questions across multiple fields.

The signaling packets that rectal cells appear to release back to the nervous system have not been fully characterized. Identifying their molecular identity and tracing their pathway to the brain would strengthen the case for a true gut-brain circuit in mosquitoes.

The rectum as a sensory organ

There is something satisfying about a finding that upends expectations so completely. The research team went looking for a receptor in the brain and found it in the rectum. They expected the nervous system to run the show and discovered that gut cells were active participants in behavioral decisions.

The mosquito rectum, it turns out, is doing much more than clearing waste. It is sensing, signaling, and helping determine when the next bite will come. For a tissue that has barely been studied, it had a lot to say.