Losing Blood in the Name of Science
A few weeks ago, Ulrich Bernier hiked along a swampy trail in Florida's Everglades, pulled back his sleeve, and absorbed 56 mosquito bites in 30 seconds. "My arm was coated," said Bernier, a research chemist with the U.S. Department of Agriculture's Agricultural Research Service in Gainesville, who counted the mosquitoes before covering his arm. His blood sacrifice was all part of the job for Bernier and a group of scientists that devote themselves to the study of Alaska's most irritating insect.
In the Everglades, Bernier was testing the effectiveness of repellants. He typically spends time in the lab, where he detects chemicals wafting from human skin. Because people give off these compounds in different concentrations depending on what they eat, what cologne they use, if they smoke, and other variables, some people are more attractive to mosquitoes than others. By analyzing glass beads that volunteers roll in their palms until skin compounds adhere to the glass, Bernier and his coworkers have found that people emit more than 300 chemicals, and as many as 30 may be attractive to mosquitoes.
Using different combinations of chemicals in mosquito chambers, Bernier and others found a secret blend of three that always brings the mosquitoes buzzing. Bernier uses these chemicals to draw mosquitoes into traps so researchers can figure out how many of the insects in an area and identify their species. No mosquitoes are known to make people sick in Alaska, however mosquito species elsewhere can spread encephalitis, dengue fever, malaria, and other fatal diseases. Seductive chemicals also can lure the insects into traps that concentrate them in areas away from people. USDA scientists in Gainesville have studied mosquitoes since 1968, when they discovered the mosquito that spreads yellow fever is attracted to lactic acid, which is emitted by human skin.
In 1997, Bernier and colleagues from the USDA and University of Florida applied for a patent on the three-chemical combination of mosquito attractants they found. Recently, they made another discovery: a chemical that masks the attractive compounds given off by people. Their breakthrough came when Bernier was testing mosquitoes in a glass chamber that allows mosquitoes to decide if they want to fly toward clean air or toward air spiked with the three-chemical compound known to attract them. Typically, about 90 percent of the mosquitoes fly toward the attractant. By adding different chemicals to each test, Bernier noticed one that stood out. When Bernier added the inhibitor chemical, the number of mosquitoes choosing the path to the attractants dropped to about 6 percent.Bernier won't identify the mystery chemical until the USDA gets a patent. He said the substance leaks from every person's pores, though in very low amounts.
By knowing the compounds that both attract and inhibit mosquitoes, researchers could someday develop a pill that curbs the emissions mosquitoes prefer and increases the release of the compound that keeps them away. Bernier said he isn't sure if large amounts of the masking chemical would be toxic, and he is just beginning to test the addition of other chemicals that may make the inhibitor even more effective. "This is so new, we haven't had time to check all the possibilities," he said.
