Mosquitoes have discriminating tastes

Mosquitoes find their hosts through a keen sense of smell.

August 26, 1999
Web posted at: 1:40 p.m. EDT (1740 GMT)

If you are convinced that mosquitoes have a greater affinity for you than for others, you may be correct.

In a study to determine whether the tiny vampires choose their victims or feed indiscriminately, University of Florida entomologist Jerry Butler and research assistant Karen McKenzie found that mosquitoes do, indeed, choose.

"Undoubtedly, mosquitoes have preferences," Butler said. "People do differ, and in any group of 10, one person will be fed on more than others."

Mosquitoes have evolved and survived — even thrived, Butler points out — because of their ability to choose the best hosts for their blood meals, which they need to lay eggs. They find their hosts, initially, through a keen sense of smell.

People can attract mosquitoes from 40 miles away simply by breathing. When a person exhales, their carbon dioxide and other odors mix to produce a plume that travels through the air. The plume acts like a dinner bell to mosquitoes, letting them know a juicy meal is within range.

Mosquitoes fly up the plume in zigzag fashion until they arrive, for example, at a backyard cookout. Then they localize on eddies of other odors in the air using vision and heat sensing to make a selection. "Mosquitoes use odor to sort attractive people from the unattractive people to find those that are most tasty," said Butler.

In order to determine the differences among individuals, Butler and McKenzie have been screening materials to determine whether they attract or repel mosquitoes. They built an olfactometer, a machine that measures mosquitoes' preferences for various odors, and connected it to a computer.

Small discs of cattle blood and odoriferous gel are covered with a membrane to mimic skin, and then mosquitoes are released into the olfactometer. When a mosquito chooses a "host" and feeds, an electrical charge is transmitted to the computer, which records the feeding. Butler and McKenzie can then analyze the data to determine which substances the mosquitoes found most attractive.

They theorize that mosquitoes, who need cholesterol and B vitamins but can't make them on their own, can sense which host is the richest source of these ingredients. Lactic acid and uric acid are highly attractive, Butler said.

Lactic acid and uric acid are highly attractive to mosquitoes.

"The things you put on your skin to soften it and make you beautiful can also be very strong attractants," Butler said. "Many of the ingredients in cosmetics will attract mosquitoes. And while a repellent may offset that, most times the cosmetics and creams last longer than the repellents."

Medications, too, can change an attractive person into one who is repellent or vice versa. Mosquito magnets include heart and blood pressure medicine and drugs to treat high cholesterol.

McKenzie saw this effect firsthand when a research volunteer was diagnosed with a brain tumor in the middle of her experiment. Before his tumor was removed, he was repellent. After surgery, however, he became very attractive to mosquitoes.

Past studies, Butler said, have tried to average materials from different individuals. But in doing so, the attractants and the repellants are averaged, he said, and individual differences are not as striking.

This is particularly important when it comes to preventing mosquito transmitted diseases. "If you reduce the feeding rates just a little, you reduce the probability of transmission of diseases greatly," Butler said. "Only one mosquito in a thousand carries disease organisms.

"People who think they attract mosquitoes are the ones at largest risk of mosquito-borne disease," Butler said. "They'll have a hundred mosquitoes feed on them when a normally repellent person might have five. It's that kind of ratio."

Copyright 1999, Environmental News Network, All Rights Reserved

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