Published on 04/09/02

Hormone Studies May Offer Mosquito Controls

The sun fades into dusk. All is good. Then you hear that buzz. Mosquitoes. Ouch! All you can do now is reach for the spray or dash inside.

A University of Georgia scientist, though, is searching for better options. He's finding out what makes a mosquito be a mosquito.

It's all in the hormones, says Mark Brown, an entomologist with the UGA College of Agricultural and Environmental Sciences. By studying the chemical messengers in mosquitoes, scientists may be able to develop novel control measures in the future.

"What we do is identify the hormones that are released after a mosquito takes a blood meal," Brown said. Female mosquitoes need blood meals to stimulate reproduction.

"Those hormones then do different things to tissues in the female," he said. "Ultimately, two to three days later, the female is ready to lay her eggs."

Female mosquitoes can live a few months. During her life, she can take a blood meal every three to four days. But she may not get all the blood she needs from one host. It may take several small meals from many hosts before she gets a full belly.

The Difference

"We're learning how similar mosquitoes are to other animals," Brown said. "The hormones are similar to other animals, like humans, cats, dogs, fish, grasshoppers. They all more or less use the same chemical messengers to guide the process that makes mature eggs."

However, with all the similarities, mosquitoes do have some small differences. And that's where Brown is concentrating his research.

A particular reproductive hormone in the mosquito brain isn't found in humans.

"We might be able to disguise a chemical, or a mimic, to disrupt its message," he said. The mosquito would not be able to reproduce if it was exposed to the chemical mimic.

He has also identified a peptide hormone that controls host-seeking behavior. It's possible that if this hormone could be injected into the female, she wouldn't be interested in taking a blood meal.

"We do the basic research," Brown said. "Then, at some point, it goes from our lab to an interested private party (to be developed)."

Deadly Nuisance

While mosquitoes can be extremely bothersome to anyone outside as dusk falls, they can be much more than just a nuisance. "Around the world, mosquitoes can carry a variety of diseases," Brown said.

When female mosquitoes take blood meals, they can also pick up pathogens that cause disease. They can carry diseases such as malaria or West Nile Virus and nematodes that cause heart worms in animals.

The disease pathogens can live, grow and mature in the mosquito. Then, when the mosquito takes another meal, they can be passed on to another host through the mosquito's saliva.

Tough Alien

The yellow fever mosquito used to be the predominant mosquito in Georgia. However, in the past decade, it has been pushed out by a much more aggressive foreign invader, the Asian tiger mosquito.

This tenacious little alien made its way to American shores in tires. "At the time, the United States was a major tire dump for the world," Brown said.

The Asian species was first reported in port areas. It has since, because of its more aggressive nature, "swept through the South," Brown said.

Many questions about this species remain unanswered. Does it carry West Nile Virus? Heart worms? Other diseases?

"Every day we have more and more tools available," he said. "And every day we're learning another small aspect of the process and putting the puzzle together."

Brown's research is funded by the National Institutes of Health.

Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.