There’s no ignoring it. Some of the students enrolled in this medical entomology class are far more attractive than others. They know it, their classmates know it, and so does Susan Paskewitz, professor and chair of the Department of Entomology.
Paskewitz describes herself as “relatively unattractive,” and she proceeds to prove it using the same test her students have just performed. She fills a small vial with warm water, rubs it between her palms to coat it with volatile compounds from her skin, then places the vial on top of a thin membrane stretched over the top of a plastic container akin to an economy-sized ice cream tub. She invites a visitor to do the same.
Waiting on the other side of that membrane are 20 blood-starved specimens of Aedes aegypti, commonly known as the yellow fever mosquito. Hungry as they are, the insects don’t show a lot of interest in Paskewitz’s vial. They hover near where it touches the membrane, but only two or three land. The visitor’s vial, on the other hand, is a busy spot. At least a dozen have landed and are testing the surface with their needle-like proboscises.
“Wow,” says Paskewitz. “You’re really attractive!”
In another context, those three words could make your day. But not here. Nobody wants this kind of animal magnetism. Nobody wants to be the person who’s cursing and slapping and reaching for the DEET while others are calmly eating their brats and potato salad.
If you’re that person, take heart. Paskewitz can tell you a little bit about why you might have more than your share of interspecies charisma and offer some suggestions on how to scale it back. But first, let’s talk about why this matters.
An average American adult outweighs an average-size mosquito by about 30 million to one. Ounce for ounce, that’s like the USS Nimitz vis-a-vis a good-size duck. But while it’s a safe bet that a 100,000-ton aircraft carrier won’t change course to avoid a six-pound mallard, it’s almost certain that, on a regular basis, you change your behavior to avoid being bitten by a 2.5-milligram mosquito.
Mosquitoes cause us to do things we’d rather not, like dosing ourselves with a repellent that’s sticky and smelly and comes with a sobering warning label (you can apply it to your kids’ skin, but keep the bottle out of their reach), or pulling on long pants, long sleeves, a hat and maybe a head net on a sweltering midsummer day.
Mosquitoes keep us inside when we’d much prefer to go out. In the summer of 2009, Paskewitz and environmental economist Katherine Dickinson, of the Colorado-based National Center for Atmospheric Research, asked a sample of Madison residents how they coped when mosquitoes got fierce.
The second-most-common answer (right after applying repellent) was to stay indoors. About two-thirds of the respondents said they had curtailed outdoor household activities—gardening, yard work, sitting on the deck—in the past month because of mosquitoes, especially in the evening hours, which, for working people, may be the only time available to get a little fresh air. About a third said they had avoided outings, and a similar share said they had avoided outdoor exercise.
Nobody wants to be outside more than John Bates, of Manitowish. An author of seven books about Wisconsin’s north woods and a naturalist by trade, Bates leads interpretive hikes year-round—except in June: “We just kind of throw the month out. The mosquitoes cause too much discomfort for people to listen to interpretation. All we can do is keep walking. People hire me because they want to learn more about the place than they knew before they came. If they can’t stop to listen, what’s the point?”
If we do venture out when mosquitoes are massing, we may not get the experience we were hoping for. Andrew Teichmiller, an outfitter of bikes and paddling gear in Minoqua, recalls mountain biking in 2014, arguably the area’s worst mosquito year ever. “You had to ride the complete trail without stopping, all the way back to the parking lot, and jump in the car, quick, because if you stopped there were 15 or 20 mosquitoes on you immediately.” As for camping: “It’s a different type of experience when you can’t sit by the fire at night and tell stories. You’re forced to run for your tent. It definitely affects the feel of the trip.”
But let’s be clear: A ruined camping trip is far from the worst possible consequence of a mosquito bite.
Mosquitoes transmit diseases that kill nearly a million people every year and sicken hundreds of millions. Tropical and subtropical areas bear the brunt of this, but no place is immune, including Wisconsin. Malaria plagued the immigrants who settled in Wisconsin in the 1800s, and various types of encephalitis are diagnosed on a regular basis.
But today the biggest concern is West Nile virus (WNV). Wisconsin has been relatively lucky since the first case arrived here in 2002, with a total of 230 cases reported through 2014. But all four adjacent states have had bigger outbreaks—notably Illinois, with 2,093 cases total and 884 in its worst year, most of them just across the border in the Chicago area. Wisconsin’s worst year brought 57 cases.
Most cases of WNV bring no symptoms, according to the Centers for Disease Control, but about one in five can involve a fever, headache, body aches, vomiting and a fatigue that can last for weeks or months. Fewer than 1 percent of WNV victims display severe neurologic symptoms, including disorientation, coma, tremors, seizures or paralysis, and of those, about 1 percent die.
Nevertheless, Wisconsin residents are bothered much more by the nuisance of biting mosquitoes than they are worried about West Nile virus. The Madison residents responding to Katherine Dickinson’s 2009 survey said they’d be willing to pay an average of $149 for a hypothetical program to control nuisance mosquitoes, but wouldn’t pay anything for one targeted at mosquitoes carrying WNV when risks were as low as they were at the time (about one case per year in Madison with a population of 250,000).
It’s not surprising to find that attitude in Wisconsin, where mosquito-borne disease is relatively rare, but Dickinson says that people tend to think the same way in places where mosquito bites are often fatal. She observes that in Tanzania, biting mosquitoes were a major factor motivating people to use bed nets. “It was a similar situation to ours,” she says. “Some mosquitoes are more noticeable and more of a nuisance, but those that transmit malaria are kind of sneaky; people don’t feel them biting as much. In areas where mosquitoes were more of a nuisance, people used the bed nets more.”
Biting-wise, there’s an important distinction between nuisance mosquitoes and the ones that transmit WNV. The former come at us aggressively, in such staggering numbers that they’re impossible to ignore. They remind us to protect ourselves. Culex pipiens, the WNV vectors, are more subtle and harder to notice.
Nuisance mosquitoes and the WNV carriers also show up at different times. The most annoying biters—Aedes vexans in particular—are floodwater species that breed after a stretch of wet weather. Culex breed in water that stagnates during a dry spell.
“When it’s been really dry, the water just sits in the stormwater catch basins that are the biggest sources of the WNV vectors,” says Paskewitz. “There’s not enough rain to flush them. Things get more fetid, stinkier. That’s the year when we see a ton of Culex.”
The take-home message: If you only grab the DEET when the biting is so bad that you can’t stand to be without it, you’re not protecting yourself against West Nile virus.
“You need to protect yourself against bites even if you’re not getting a lot of them,” says John Hausbeck, director of environmental health services for Dane County and the City of Madison. “We’ll see summers where it’s really dry and the floodwater mosquitoes are very limited, but we still have plenty of small pools that the Culex can breed in.”
That “biting pressure” is something that Hausbeck needs to stay on top of, and Paskewitz helps with that. She and former grad student Patrick Irwin PhD’10 were able to characterize the types of sites where Culexare most likely to breed and identified alternatives for treating them—for example, introducing fathead minnows to feed on Culex larvae. She and her students analyze the mosquitoes trapped in the area to see how many are Culex and whether they’re carrying WNV. Their data tell Hausbeck whether he needs to issue a public alert.
It’s important to remain vigilant. “When West Nile first came into the country, people doubted it would make it through the first winter,” Paskewitz says. “Well, it did persist, and in a very short period of time it whipped across the whole country. We’ve had a lot of cases in new places. First it was really bad in North and South Dakota. Then Colorado and Arizona. Then Texas, Illinois. It’s really hard to predict. And given the vagaries of climate, we just don’t know whether the next year it might be Wisconsin.”
Continue reading this story in the Fall 2015 issue of Grow magazine.