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Fighting the Asian tiger mosquito

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The talk at the community garden in late summer is not about the tomato harvest, or the need to clear beds for fall greens. It’s about those little black mosquitoes that have made life outdoors such a pain. A pain for us, that is, not the mosquitoes. They are after our limbs for a little sip of blood, which gives them the protein to develop eggs for even more mosquitoes and gives us an itch, a welt and the risk of catching a nasty disease. For now, this particular parasite — the Asian tiger mosquito— is more a nuisance than a public health threat. The blood-sucking adults typically appear in June, peak at this time of year and then die off in October. It is not the species associated with the spread of West Nile virus, though that could change, entomologists say. But the imported pest has become so widespread and numerous that it is changing the way we live.

As my gardening neighbor proclaimed as he stalked off the other day: “The best DEET is the inside of my home.”

We started to become a nation of insiders between the world wars, when public health authorities urged us to live behind screens as they sought to eliminate malaria. And then air conditioning served to draw us inside even more.

But before the advent of the Asian tiger mosquito, our main periods of summer retreat were at dawn and dusk, when native mosquitoes tend to bite. Now, the day-feeding Asian species has sort of sealed the lid. We might think of ourselves as masters of the universe, but in the human-bug equation, we are the ones in the glass jar.

As entomologists continue to seek ways to fight the Asian tiger mosquito, they warn that there is no magic bullet to make it go away. Instead we can reduce its nuisance value if we collectively adopt an approach called integrated pest management. It sounds fancy, but many of its principles are basic, such as removing flowerpots that trap water and clearing your gutters, especially in spring at the start of the breeding season.

How it got here

Like so many invasive exotics, the Asian tiger came to us by way of globalization: It was discovered in Texas in 1985 and traced to a shipment of used tires from Japan, according to a scientific paper in the Journal of Medical Entomology.

Unchecked, the species soon got a foothold in the Houston area and spread north and east, and is established today in at least 30 states and the District. It reached Northern Virginia in 1997, was found earlier in Baltimore, and now extends to the southern fringes of New York.

It is called the tiger mosquito for its stripes: white markings on its legs and body that also give it its scientific species name, Aedes albopictus. It is so unlike other mosquitoes that standard strategies to beat it back have been ineffective.

Mosquitoes lay eggs near water, and the larvae develop aquatically, pupate and fly off as adults. Many species do this in broad marshes and swamps, but the tiger mosquito evolved to grow in little pockets of rainwater trapped in tree trunks and leaf joints.

When it made its switch from the forest to the city, it found its human victims had given it an unbelievable array of breeding locations: birdbaths, empty soda cans, tires, creases in tarpaulins, plastic toys, wheelbarrows, anything that could trap water, if only for a week or two. It needs so little water to breed, it can reproduce in upturned bottle caps and the little depressions in black corrugated drainage pipes. Scientists call all these various reservoirs containers and the pest a container-mosquito.

Its behavior was different, too: Many native species feed at night on sleeping birds. The tiger mosquito prefers to feed on mammals, and during the day. It lies in wait and ambushes its victims. It is a weak and low flier and tends to favor the nether parts of the mammal human, biting our ankles and lower legs.

How to protect yourself

The obvious ways to counter the insect are to remove all sources of standing water on your property and urge neighbors to do the same; wear clothing that covers the body; and put some repellent on exposed skin. But as with everything else, it’s more complicated than that.

With this mosquito, eliminating the containers isn’t that easy.

Joseph Conlon, an entomologist with the American Mosquito Control Association, said he went to a house near where he lives in Florida to see an owner who said she had diligently removed all standing water. In her yard, he counted 123 containers where tiger mosquitoes could breed. “Cans dumped in bushes and stuff,” he said.

Clothing? I would not dream of gardening in the summer without long pants, socks, shoes, a shirt and a hat, and, for much of the toil, gloves. Looking around at others, I ask myself if I’m not some sort of kook. I see men, women, and children in shorts and flip-flops. Why not add a tattoo across your forehead: Diner Open.

Effective repellents

This brings us to repellents. The most effective, still, is DEET, developed for troops to use in the jungle. But in rare cases, DEET has been linked to skin injuries and even poisoning, especially for children, and a lot of folks are leery of it.

The EPA says registered brands are safe if used as directed. For prolonged protection, the Centers for Disease Control and Prevention recommends products with at least 20 percent DEET but says anything over 50 percent is overkill. The American Academy of Pediatrics doesn’t recommend its use on children younger than 2 months old. You must follow the directions, which say keep it out of your eyes and don’t put in on the hands of young children, who tend to stick their fingers in their mouths.

If you don’t want DEET, the EPA says other repellent compounds are also safe and effective when used properly: namely Picaridin, a synthetic version of pepper plant compounds; lemon eucalyptus oil, and a compound named IR3535.

“The best repellent is the one you’ll use religiously,” said Jorge Arias, a supervisory entomologist at the Fairfax County Health Department.

In my little veggie garden, I have used a repellent with 98 percent DEET (this was before I read the CDC advice) and it seems to work for several hours, though it leaves you feeling like an oiled salmon. I have asked visitors to try lemon eucalyptus oil, and that also seems to keep the mosquitoes at bay. I also purchased a citronella oil candle in a tin, but the wick got damp and I couldn’t get it to light again.

In addition, I bought a pack of five mosquito sticks, each about a foot high and impregnated with a repellent. Once I got them lighted and smoking, which took several attempts, they did seem to keep the area free of the mosquito, but they were done after three hours. At $4.50 a box, they might be affordable for the occasional barbecue, but not an afternoon’s gardening.

Homeowners can also buy sprays that kill adult mosquitoes — or, increasingly, hire pest control applicators to do it for them. The pesticides consist of compounds called pyrethroids, which are considered of low toxicity when used correctly, though in the wrong hands they can kill fish, bees and other beneficial insects.

The problem, apart from the cost if you contract with a company — typically $400 to $700 for regular sprays between late April and late September — is that spraying the adults alone isn’t going to keep the mosquitoes away: New ones keep hatching. Damien Sanchez, owner of the Mosquito Squad of Greater D.C., said the regular sprays reduce adult numbers by 80 to 90 percent. His workers use backpack sprayers to treat more than 1,000 area homes weekly.

The secret to managing this pest is for everyone to engage in a concerted effort to deny the overwintering eggs a chance to develop in the spring when rains fill every potential container, said Dina Fonseca, an associate professor at the Rutgers Center for Vector Biology in New Brunswick, N.J. She and her colleagues at the center have been studying tiger mosquito management in an agreement with the federal Agricultural Research Service, based in Beltsville. “The population is reset every winter. We can try and develop a program that controls them right at the start of the season. By not letting the population go crazy, you may not have big problems later. That really is the enlightened approach.”

And get some long pants.

How to fight mosquitoes

what works

Clothing: Loose-fitting garments will minimize skin exposure and feeding sites. Tuck pants into socks; the tiger mosquito loves ankles and lower legs. Light colors are less of a draw. Clothing sprayed with a repellent or an approved insecticide will add protection, but don’t apply pesticides to the skin.

Repellents: DEET is still considered the gold standard, use concentrations between 20 and 50 percent. The EPA has approved these other repellents as safe and effective, sold under various brand names: picaridin, IR3535 and oil of lemon eucalyptus.

Remove standing water: Tiger mosquitoes can develop in an ounce or less of water. Flush out birdbaths at least every week. Police your yard to remove all sources of standing water, including creased tarpaulins and clogged gutters. Urge your neighbors to do the same.

LIMITED VALUe

Citronella: Candles, torches and wicks containing oil of citronella are less effective than repellents and of little use in a breeze.

Insecticide sprays: Pyrethroid sprays will bring a temporary respite from adult mosquitoes, but they’ll be back. The sprays can kill bees and fish. Many experts consider automatic misting systems to be environmentally irresponsible.

Traps: Traps based on luring mosquitoes through attractants are somewhat effective but won’t stop you from getting eaten.

FUGGEDABOUTIT

Purple martin and bat houses: Both bird and mammal eat many insects on the wing, but mosquitoes represent a fraction of their diet.

Bug zappers: These draw and electrocute nocturnal insects but relatively few mosquitoes. They kill beneficial insects without alleviating the mosquito problem.

Diet: Eating garlic or taking Vitamin B12 will not naturally repel mosquitoes, as is widely believed.

Sources: American Mosquito Control Association; Centers for Disease Control and Prevention; EPA; Rutgers University

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Chat Thursday at noon Join Higgins for a live Q&A about mosquitoes and gardening . Gardening archive Read past columns by Higgins, including those on boxwood blight, angel’s trumpet and the the plight of the urban forest.

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