Pestology Blog

Because of their significant threat to public health, controlling these tiny disease-carrying vampires is high priority. Especially when it comes to managing Anopheles mosquitoes, which are the group of species that can spread malaria. A common way to protect against mosquitoes is to eliminate the insects themselves using adulticides or larvicides. One challenge with these options, however, is that mosquitoes can develop resistance to insecticides, reducing their effectiveness.  

Another approach to mosquito control is to disrupt the host-seeking behavior of mosquitoes, preventing hungry females from being able to find their next bloodmeal. Mosquitoes use a combination of cues to locate a host, but chemical cues are often the most important signals they rely on. Using their highly specialized antenna, mosquitoes can detect the chemicals and compounds in our breath, sweat, and through our skin. Scientists have identified that there are over 300 different compounds (and counting) emitted by human skin. While some of these compounds are known to be attractive, not all of them are important in host location. Knowing which of these chemicals attract mosquitoes may hold the key to understanding how they find a host and, importantly, how we can exploit this information to develop more effective attractants or repellants. But, that task is easier said than done because identifying the chemicals is only half the battle. You also have to determine the right concentration and mixture. Because even the slightest deviation in formulation can turn an attractant into a repellent or render it ineffective all together.  

Lucky for us, a team of scientists collaborating across four Iran-based university and government research agencies have been working to get us one step closer to unlocking this mystery. Using the important malaria vector, Anopheles stephensi, the researchers evaluated the attraction of four chemical compounds found in human skin and breath, each tested at 5 dilutions under laboratory conditions. Picking these compounds wasn’t a total shot in the dark since previous studies have already demonstrated their effectiveness as attractants with other mosquito species.  

To start, researchers tested the response of non-blood-fed An. Stephensi to the four candidate compounds at various dilutions using a dual-choice (or y-tube) olfactometer (Figure 1). An olfactometer is a specially built chamber that offers mosquitos two different air streams that can each be mixed with a different chemical. By releasing mosquitoes into the chamber, researchers can record which airstream the mosquitoes prefer, allowing researchers to measure attraction or repulsion of the chemicals being tested.

For each experiment, the airstream contained either carbon dioxide alone, or carbon dioxide mixed with one of the test chemicals. Adding the carbon dioxide to air streams was needed for all experiments because CO2 is required to trigger the host seeking response in mosquitoes. Once the four compounds were screened, the top three performers were used to create five new blends of the chemicals and the olfactometer tests were repeated.  

Until this point, I’ve spared you the trouble of having to listen to me read off the names of the chemicals tested. But, I will list out the names of the chemicals that were the big winners. When testing the chemicals individually, hexanoic acid produced the highest consistent attraction to An. stephensi compared to the other three treatments. When the blends were tested, the mixture of hexanoic acid with 3-methyl-1-butanol produced the highest overall attraction.  

Both Hexanoic acid and 3-methyl-1-butanol are human skin volatiles associated with the human odor profile and have been shown to be important attractants to other mosquito species in similar studies. With hundreds of chemicals being produced from our skin, and thousands of combinations to test, every bit of data we can collect on these compounds and how mosquitoes respond to them is vital. This study added a few more chemical blends to our list of known attractants while, importantly, helping to cross off a few others that didn’t seem to move the needle. By pinpointing which human skin volatiles attract malaria‑carrying mosquitoes, studies like this bring us one step closer to developing next‑generation attractants and repellents. With further testing in the field will be required for these blends, these insights may one day lead to the development of practical tools that protect vulnerable communities around the world against Malaria and other deadly diseases.