Forget the mosquito repellent. Jack Gingrich doesn't go on stakeouts in salt marshes at midnight because he wants those persistent little pests to stay away. He wants them to use him for a landing zone--which they do, in squadrons.

"I don't need to lure them, either," the UD entomologist says with a chuckle. "Salt marsh species are more prolific than others. They come quite well on their own, by the hundreds!"

Gingrich, a medical entomologist and researcher in the College's Department of Entomology and Applied Ecology, recently completed a study aimed at identifying which mosquito species in Delaware pose a high risk as carriers of West Nile virus. Thus far, he has identified 28 of 55 species known in the state from four collection sites. Eight of the species have been discovered to be high risk.

The West Nile virus, which has been spreading steadily throughout the eastern United States, has infected three horses in Delaware in the past year, one fatally. In addition, dozens of birds have been infected. Gingrich thinks there's a high probability that the state won't escape a case of human infection next time around.

"All the conditions are established," he says. "More than 55 people nationwide fell ill with West Nile in 2001, and six did not survive. While the disease is usually mild among healthy adults, it's the elderly, the very young and those with compromised immune systems who are at risk.

"By identifying which mosquito species pose the greatest threat as carriers, learning where they breed and how often, we can target our mosquito control efforts and partially contain the disease throughout the state."

The researcher finds that his quest for mosquito specimens takes him to some dreadfully inhospitable locales at some awfully uninviting hours.

"Mosquitoes do most of their feeding from 7 p.m. to midnight and from 5:30 a.m. to 8 a.m. They tend to breed in smelly, slimy spots. So, if I want to find samples, I have to go where and when they go," he says.

That takes Gingrich not only to coastal salt marshes but also to nasty puddles of water. He found plenty of those at Delaware Park racetrack, where highly valuable racehorses are vulnerable to infection.

"We discovered a high-risk carrier breeding in the pools of water, mud and manure that form when the horses are washed down each day," he says. "Since horses have been infected in the past, we reported our concern to the New Castle County mosquito control authorities, who treated the breeding area with a highly effective larvicide, virtually neutralizing that mosquito as a threat in transmitting West Nile at the racetrack."

Such targeted mosquito control efforts are key to minimizing risks to animals, humans and the environment, Gingrich says.

"Targeting allows authorities to treat smaller areas and catch the insects at the larval stage, before they become dangerous," he says. "It's less costly and less time-consuming to spread a good larvicide in a small area than to broadcast an 'adulticide' randomly, and it's less harmful to other species.

"We can adopt other environmentally friendly methods of control, too, such as opening salt marsh trenches to flush out standing water. This removes the mosquitoes but saves their natural predators from harm. In addition, physical methods don't pollute soil and water with chemicals."

The veteran researcher, who has spent many years studying such mosquito-borne diseases as malaria, dengue fever and Japanese encephalitis, expects to continue his work with Delaware mosquitoes in the 2002 breeding season.

"We plan to study different sites--something urban or suburban, in addition to coastal wetlands east of Dover," he says. His plans also include collecting risk data from a larger number of mosquito species. Grants received through the state from the Centers for Disease Control will help finance the research.

Gingrich notes that only about one in 1,000 mosquitoes is infected with West Nile virus, and only about one in 300 people bitten by such a mosquito becomes infected. Despite this relatively low risk of human infection, he says, it's important to get a handle on the disease now.

"West Nile virus is here to stay," he says. "When we identify the high-risk carriers and their habits, we limit the potential threat, protect human lives and valuable livestock and guard our environment from possible deadly consequences."

--Marianne Kirby Rhodes