Why Researchers Can't Control Mosquitoes

We had barely stepped out of our car in Canada's northern Yukon Territory when the siege began. Dark clouds descended out of nowhere as seemingly zillions of mosquitoes dove in for the kill.

Over the next two weeks, as we tried to enjoy our vacation, these monstrous little critters plunged their sharp needles into our bodies, sucking out our blood, defying every effort to chase them away. It seemed like our usually effective bug repellants were attracting them instead. They ate through our clothes, leaving welts across my wife's back (they found her more tasty than me) and more than once our only defense was to pack up and leave our campsite.

The situation bugged me, so to speak, so much that I decided to find out if we are anywhere near winning the war against mosquitoes. One expert after another answered my question essentially the same way.

In a word, the answer is no.

We're winning a few skirmishes, and there is some progress to be reported, but the war is definitely not in our favor.

Mosquitoes Have the Numbers and Advantages

"Mosquitoes will probably be here a long time after we are all gone," says biologist Douglas Carlson of the American Mosquito Control Association.

"I don't think we're even close to eradicating or removing mosquitoes from our environment," adds Donald R. Barnard, who heads the mosquito unit at the U.S. Agricultural Research Service's Center for Medical, Agricultural and Veterinary Entomology in Gainesville, Fla.

There are around 3,000 mosquito species around the world, about four or five dozen of which are of concern to humans because they can transmit serious diseases. Female mosquitoes need blood (males don't bite) to produce their eggs, so they are annoying as well as potentially deadly.

They have proven to be so adaptable to changing environments that they've "pretty much handled everything we've thrown at them," says Barnard, whose lab none-the-less has made some progress.

There are several factors that tilt the playing field in the mosquito's favor. There's relatively little money to be made in producing chemicals that can kill mosquitoes so major chemical companies are reluctant to make the kind of investment that could lead to success. And mosquitoes tend to settle and reproduce in environmentally sensitive areas, making it much more difficult to kill them off without seriously damaging the environment.

In the old days, entire lakes were drained to kill off mosquito larvae, but that also eliminated the lakes for a wide range of other users, including humans and wildlife. That's now a no-no because it falls in the range of throwing out the baby with the bath water.

"It's a question of balancing mosquito control needs with protecting sensitive environmental habitats," says Carlson, who chairs the environmental protection committee for the mosquito association.

One Possibility: Drown 'Em

The association has worked to improve the current method of controlling mosquito populations that breed in saltwater marshes, a major source for several species of mosquitoes.

These mosquitoes lay their eggs on moist soil in the marshes, but they won't lay them on standing water like many other species. So a few decades ago it was learned that if dykes were built around the marshes, a little fresh water could be pumped in, flooding the breeding areas.

It doesn't take much water to wipe out the mosquito habitat, Carlson says, but any alteration of the natural environment has some adverse affects.

Continuing the practice of flooding saltwater marshes without wiping out the habitat for other species is one of the primary goals of the mosquito association, which operates under the auspices of the federal Environmental Protection Agency. The program has been somewhat successful, but as anyone who has visited Florida in the summer knows, millions of mosquitoes are doing just fine, thank you.

Death by Infection and Death Traps

Barnard's lab has made some progress in a couple of promising areas. For example, some viruses have been known to kill mosquitoes, but scientists have been frustrated in their efforts to come up with a way of transmitting the virus to the mosquitoes.

Researchers at the lab have, for the first time, figured out a way to do that. By blending certain chemicals with the virus, Barnard says, they have transmitted a virus that kills some mosquitoes, specifically the mosquitoes in the Culex genus that carry St. Louis encephalitis. That is the most common disease transmitted to humans by mosquitoes in the United States. Mild infections can cause headaches and fever, but severe cases can cause convulsions, paralysis, or even death.

Entomologist James J. Becnel of the Gainesville lab says that in a field test case, the treatment killed 60 percent to 70 percent of the mosquito larvae over a 48 to 72 hour period.

So far, the tests have indicated that the virus is not harmful to other organisms, including humans, but more testing is needed.

Another idea is to come up with a means of attracting mosquitoes to a designated area where they could be ambushed. That's just what Barnard and other researchers have been trying to do, and with some success.

Mosquitoes are guided to their targets by several factors, including sight, infrared radiation, and exhaled carbon dioxide. So the researchers have been zeroing in on specific "attractants" that could be used to lure mosquitoes into a trap. Old socks work quite well, provided they've been worn long enough. Limburger cheese is pretty good. But carbon dioxide is very effective.

That means a mosquito can smell your breath from a long ways away. So Barnard and his colleagues are developing a sniff-and-die trap. Carbon dioxide and other attractants are released near the trap, which works a little like a sophisticated vacuum cleaner. The bug sniffs the scent, zeros in, and gets captured by the wind from a small fan, forcing it into a bag.

You'll probably be able to buy one of these gizmos one of these days soon, but don't expect it to cure the mosquito problem. Even Barnard admits it might only work well in a back yard, or another urban setting, where the mosquito population is relatively low.

"It's not going to work very well where you've got a horrendous number of mosquitoes," he says.

It sure won't solve the problem for the Yukon, where horrendous is an understatement. And incidentally, our problem there was one of poor timing. A hot spell, following a rainy summer, was all the bugs needed to ruin ours.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska. He will not have a new column for the week beginning Aug. 20.