Tiger Mosquito Invades the U.S.

ByLee Dye

July 26, 2001 -- For those folks who live in the far north and find some comfort in the idea that the planet is getting warmer, here's a bit of bad news: Hordes of nasty mosquitoes may be heading your way.

Ever since it was accidentally introduced into the United States in the 1980s, the Asian tiger mosquito has expanded its range faster than a prairie fire and it now makes its home throughout the Southeastern states. And now researchers have shown it only takes a slight increase in temperature for these ferocious little biters to propagate like overzealous bunnies.

Barry Alto, a doctoral candidate in entomology at the University of Florida, and Steven Juliano, a biology professor at Illinois State University, kept three groups of Asian tiger mosquitoes at different temperatures — 79, 75 and 72 degrees Fahrenheit. The goal of the research, which was done while Alto was finishing up his masters degree at Illinois State, was to see how the little pests performed at different temperatures.

"We were able to show that populations at higher temperatures had extremely high rates of population increase, and that the population increased very rapidly initially," Alto says. "That's important because according to population dynamic theory, organisms are better able to get a foothold in new sites when they grow really quickly right in the beginning."

Unknown Consequences of Global Warming

In other words, critters have a lot better chance of surviving if they propagate like mad as soon as they arrive in a new territory.

The research, published in the July 18 issue of the Journal of Medical Entomology, underscores a basic challenge facing scientists today. Many serious consequences of global climate change may have little to do with inundated beaches from sea level rise — the most frequently cited result of global warming. It's likely there will be many changes, and many surprises, if the planet's weather changes as much over the coming years as many experts predict.

For example, take the Asian tiger mosquito. Please.

This is a really nasty little bug that is capable of transmitting serious diseases, according to research in various labs. It hasn't happened so far in this country, as far as we know, but the research shows the tiger can be a successful bearer, or "vector," of such diseases as LaCrosse encephalitis, yellow fever, and dengue fever.

Dinner in the Daytime

It's smaller than most mosquitoes, but its bite causes more irritation than most, and it dines throughout the day, not just at night. It's especially aggressive during its feeding frenzy. And if it lands on you, the bug is so fast it's probably going to inflict its damage and get away before you have a chance to swat it.

The tiger looks so different that it's easily identified by even the casual observer. It's black with white stripes, thus its name.

And it is on the move, big time.

The first wave of the invasion began in Houston in 1985 when some of the mosquitoes hatched out of eggs believed to have been transported to this country from Asia in old tires bound for recycling.

In about a year it was already in Jacksonville, Fla., and "within the next eight years it had spread to every county in Florida," Alto says. Within two decades it was firmly entrenched as far north as Pennsylvania and the upper Midwest.

The tiger's lifestyle helped facilitate that rapid migration.

Tigers are known as "container breeders," meaning they don't need a nice lagoon to bear their young. Instead, they prefer smaller pockets of moisture, like holes in trees that collect rainwater. In fact, any container will do, especially old tires because they are so good at retaining moisture, according to Phil Lounibos, professor of entomology at the University of Florida, who has spent several years researching the mosquito.

That affinity for small containers made the tiger especially adaptable to human society, because we always seem to be leaving something around that collects a little rainfall and makes a perfect habitat for zillions of mosquito eggs.

Mosquitoes Hitch Rides With Humans

So the population of tiger mosquitoes just "took off," Lounibos says, "partly because of its ability to hitch rides with human transport systems."

So when some community in the South collected its old tires and sent them off somewhere else for recycling, they most likely sent along an uninvited guest.

Until the research by Alto and Juliano, it had been thought that the tiger's range would be limited, but it now appears that if current warming trends continue, that range could be expanded, possibly even into Canada, Alto says.

In areas where it has become firmly established, Lounibos says, the tiger has displaced the most common mosquitoes found in those areas.

That could prove unfortunate because the tiger is likely to be far harder to get rid of than many other mosquitoes. Since it prefers some sort of a container, like an old tin can or a hole in a tree, for its birthing area you can't eradicate it by simply draining water out of a swamp.

"Control is difficult because a percentage of the population still deposits its eggs in the natural containers that formed the major habitat for its ancestors," concludes a research paper from Rutgers University. It might help to get rid of tin cans and old tires "but gaining access to larvae that are developing in treeholes is an almost impossible task," the report says.

However, it doesn't look like the tiger will take over the whole country.

Additional research by Alto and Juliano, which will be published in a couple of months, shows that the tiger doesn't mind the heat, as long as it's moist. But it can't stand the heat if its dry.

That's probably why the first wave of mosquitoes to leave Texas headed east to humid Florida instead of west to arid Arizona.

But chances are more of the country will become palatable to them if it does indeed become warmer and wetter.

Maybe they'll even make it up to my state, Alaska, where the mosquito is the unofficial state bird.

Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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