Chemicals released from the rectum control insect appetite
Mosquitoes have an appetite suppressant in their behind.
When the mosquito’s belly is full, special cells in their rectum block their thirst for bloodthe researchers report on March 20 in Current biology. This discovery could pave the way for a way to stop insects from biting in the first place.
Female mosquitoes feed on blood to give their eggs a boost of protein and other nutrients before laying them.
“We have known for decades that after females take this large blood meal, they almost completely lose their attraction to find and bite humans” says Laura B. Duvall, a neuroscientist at Columbia University.
Researchers already knew about a biochemical called neuropeptide Y, or NPY, which influences eating and feelings of fullness in a wide range of animals, including mosquitoes. Duvall and his colleagues previously found that disrupting a protein called NPY-like receptor 7 in the bodies of mosquitoes shut down NPY’s ability to quell hunger. Female mosquitoes were constantly trying to bite people, even with bellies swollen with blood.
“We knew this receptor was important, but we didn’t really know how or where it worked in the mosquito,” says Duvall.
Duvall and his team genetically analyzed different sections of the dengue mosquito (Aedes aegypti), discovering that the receptor 7 gene only created its product at the end of the intestine.
“We found it in a really unexpected place,” Duvall says. Most of these types of receptors involved in appetite and satiety are found in the brain.
Through genetic manipulation, the team lit up specific intestinal cells containing this receptor with a fluorescent protein. Labeling the cells in this way showed that there were special cells in the pads of the rectum where the receptors worked. It is these rectal pads that respond to the influence of appetite-modifying neuropeptides.
The rectal pads are close to nerve cells that release a chemical called RYamide after mosquitoes feed. RYamide interacts with rectal receptors, which then show an increase in calcium, much like a nerve cell. The cells also appear to release compounds similar to those used in nerve cell communication. Duvall and his team believe that rectal cells act much like neurons, interpreting signals that the gut is full and transmitting that message to the brain. Some cells behave the same way in mammalian intestines, she says.
Medical entomologist Rebecca Johnson of the Connecticut Agricultural Experiment Station in New Haven wants to conduct more research on how these rectal cells might influence the mosquitoes’ nervous systems. “This work indicates that mosquitoes are very complex organisms,” she says.
Future research may reveal a chemical way to trigger the appetite-reducing effect in mosquitoes before they even bite. Reducing their hunger could prevent the spread of dangerous diseases transmitted by mosquitoesparticularly because intestinal tissues loaded with receptors are much more accessible than the brain, explains Duvall.
Current efforts to curb insect activity include releasing genetically modified mosquitoes Or target your sense of smell with repellents.
“You now have a target that you can access by simply feeding the mosquitoes a compound,” Duvall says.