Mosquitoes Have Discriminating Tastes, UF Researchers Find

In a study to determine whether the tiny vampires choose their victimsor feed indiscriminately, UF entomologist Jerry Butler and researchassistant Karen McKenzie found that mosquitoes do, indeed, choose.

"Undoubtedly, mosquitoes have preferences," Butler said. "People dodiffer, and in any group of 10, one person will be fed on more thanothers."

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

All people have to do to attract mosquitoes from even 40 miles away isbreathe. As they exhale, their carbon dioxide and other odors mix toproduce a plume that travels through the airstream. The plume acts likea dinner bell to mosquitoes, letting them know a warm-blooded meal iswithin range.

They fly up the plume in zigzag fashion until they arrive, for example,at a backyard cookout. Then they localize on eddies of other odors inthe airstream and then, within yards of a person, they use vision andheat sensing to make a selection.

"Mosquitoes use odor to sort attractive people from the unattractivepeople to find those that are most tasty," Butler said. "They arelooking for the highest rates of human attractants."

What are those attractants? That's the next challenge for Butler andMcKenzie. Already they know that natural excretions through the skin andskin care products affect mosquitoes' appetite.

Take perspiration. By itself, it appears to be neutral, but as it agesbacteria begin developing, and that makes perspiration into a verystrong attractant, Butler said. Bathing helps, but some after-bathproducts don't.

"The things you put on your skin to soften it and make you beautiful canbe very strong attractants," Butler said. "Many of the ingredients incosmetics and will attract mosquitoes. And while a repellent may offsetthat, most times the cosmetics and creams last longer than therepellents."

Medications, too, can change an attractive person into one who isrepellent or vice versa. These include heart and blood pressure medicineand drugs to treat high cholesterol.

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

Such findings have added to the intrigue for Butler and McKenzie. Theytheorize that mosquitoes, who need cholesterol and B vitamins but can'tmake them on their own, can sense which host is the richest source ofthese ingredients.

In their laboratory, Butler and McKenzie are screening materials todetermine whether they attract or repel mosquitoes. They built anolfactometer, a machine that measures mosquitoes' preferences forvarious odors, and connected it to a computer.

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

Their research goes beyond relief for barbecue guests. They hope to helppeople to protect themselves from mosquito-borne diseases.

"If you reduce the feeding rates just a little, you reduce theprobability of transmission of diseases greatly," Butler said. "Only onemosquito in a thousand carries disease organisms.

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

After mosquitoes choose a host, they look for a landing strip. It's noaccident that they often land in hard-to-reach places.

"They like to feed on humans, and they know what the human response isgoing to be so they sneak in and bite when it's the least dangerous tothem to feed on you," Butler said. "Then they feed quickly, just eightto 10 seconds, and they're gone; the length of time they're on a hostregulates whether they get squashed."

If you've ever watched a mosquito land on you and noticed it doesn'tbite right away, there's a reason for that. Just any old spot won't do.

They search the skin surface with their mouth parts till they find asite that feels or tastes good, then insert their stylet. The styletmoves through the tissue "like an oil-drilling rig" working aroundobjects and turning at angles. When it detects the mother lode -- acapillary -- it taps right in.

Butler says the study has far-reaching implications for backyardbarbecues -- and who is on the guest list.

"If you can figure out who, among your friends, is attractive tomosquitoes and be sure to invite that person to all your outdoorgatherings, you might be able to spare your other guests from mosquitobites," Butler said. "In any group, there should be one person who ishighly attractive to mosquitoes."

What a price for popularity.