While studying the malaria mosquito’s nose Biologists at the University of Vanderbilt discovered that it uses different scents, rather than sight or sound, to detect humans. She actually follows the odor of the carbon dioxide, breathe out by the animals and humans, and decides whether it is desirable host or not.

A group of Biologists started their research 15 years ago with a family of 79 odorant receptors (ORs) in a bid to prevent diseases caused by mosquitoes. After a long study the researchers finally reached to a conclusion that mosquitoes have a secondary set of odor sensors that specially designed to detect human odors.In a paper published in journal Scientific Reports it is clear that this was first discovered in a fruit fly 5 years ago.

Biologists also found some interesting facts during the research that the ORs of malaria mosquitoes did not react to most of the human odors. This belief was held by scientists previously. The Secondary set of odor sensor consists of minimum two signals, which are human derived. These signals cannot be detected by the OR system of malaria mosquitoes. So, to hunt for human blood, female mosquitoes use this extra odor sensor system.

Talking about the discovery Cornelius Vanderbilt, Professor of Biological Sciences Laurence Zwiebel, who directed the study said

“This appears to be a more primitive olfactory system and one which Anopheles uses to detect humans. It fills important gaps in the mosquito’s chemosensory perception that are not provided by the OR system.”

In a series of extensive and painstaking experiments carried out for his senior honors thesis, undergraduate Stephen L. Derryberry (now a student at the Vanderbilt School of Medicine), along with Research Assistant Professor Jason Pitts, succeeded in functionally characterizing three of these different sensors, called ionotropic receptors (IRs), in Anopheles. The researchers determined that unique combinations of IRs respond to two classes of compounds found in human sweat: carboxylic acids that impart a vinegary tang and ammonia derivatives called amines.

“Stephen’s project was more difficult than simply searching for a needle in a haystack,” Zwiebel said. “It was more like searching for a needle in a HUGE haystack, because we had no idea of what odorant molecules would trigger the IR system. Even worse, we didn’t know what combinations of IR receptors might be involved.” (In flies IRs only detect target molecules in conjunction with co-receptors on the same neuron.)

There is still a great deal about the IR system that the scientists don’t understand. For example, they think the mosquitoes may also use this ancient family of proteins to detect infrared radiation and humidity levels.

One measure of the importance of an olfactory system is the number of connections it has to the brain. By this measure the OR system is the most important because it has more neurons that link it to the mosquito’s brain, but the IR system runs a close second.

“The mosquito is an extremely sophisticated organism,” said Pitts. “They use a combination of finely tuned olfactory systems to locate their prey. We have now found two of these systems, but, based on what we know about the mosquito’s genome, we think there are others that we haven’t identified yet.”

“Despite all the research we have done, we still haven’t fully figured out how mosquitoes identify and, even more importantly, develop a preference for humans,” Zwiebel observed.

Source: Nature.com