For almost 20 years now, gardeners have put up with a persistent nuisance unknown to previous generations of Americans: a stealthy parasite named the Asian tiger mosquito.
This year, the insect brings a different dynamic to our world, as a potential carrier of the Zika virus. Controlling it won’t be easy, experts say, because it thrives and spreads on the human landscape of stuff, clutter and trash.
Apart from its ubiquity, the Asian tiger mosquito is distinguished from other mosquito species by its habit of biting in broad daylight and its coloration: It is black with distinctive white markings, hence its common name and also, students of Latin take note, its scientific term, Aedes albopictus.
The invasive, exotic insect is a price we pay for our system of offshore manufacturing and globalized commerce. The tiger mosquito arrived in Texas from Japan in the mid-1980s and has been annoying Washingtonians since 1997. It is now found as far north as Massachusetts and west to Southern California.
The winged adults are first seen in May and peak in high summer, but they can remain a pest until October. With determination, the right clothing and some insect repellent, people who need or want to spend summer hours outdoors in the metropolis can go about their business. (Also, I have found that the bites of the tiger mosquito are not as irritating or enduring as those of good old salt-marsh mosquitoes.)
This coexistence may soon break down into something far more adversarial as a result of the Zika virus outbreak in Brazil, where some 1.5 million people have been infected. The virus induces a flulike illness in some and barely registers in others, but it has been linked to a grave brain condition in babies whose mothers contracted the virus while pregnant and also to an immune system syndrome.
So far, U.S. residents with confirmed Zika infections — three had been reported in the District as of Feb. 17 — picked it up while abroad, but it’s likely that it will spread to people who have not traveled. This is how Zika could migrate: A resident travels to an area with a Zika outbreak, contracts the disease and returns during the infectious phase. A mosquito takes blood from this individual, picks up the virus, incubates it and then transmits it to a second person through another blood meal.
“It’s like a hurricane,” said Gordon Patterson, an author of books on public health crises and mosquitoes. “We know it’s coming, we don’t know where it will hit, but we’ll see some indigenous cases here.”
How worried should we be? Experts are concerned but not in a panic, primarily because in the United States most people spend most of their summer hours in homes that are screened and air-conditioned — that is, sealed from nature. In poorer, tropical countries, where people live in more open shelter, mosquitoes come and go like house cats and indeed spend much of their time within the home.
The Zika culprit in Brazil is the yellow fever mosquito, Aedes aegypti, which has learned to prey on humans where they live. This species is established in the Deep South, as well, but its presence in northern states is linked to its arrival as stowaways that die off in winter. Here’s some bad news: Entomologists recently published a paper saying they had found a resident population of yellow fever mosquito that survives the winter by living in sheltered areas of Capitol Hill, perhaps in the sewers.
But it is another discovery that may prove more vexing in the United States: A laboratory study in Singapore showed that the Asian tiger mosquito can carry and transmit the Zika virus, and in a separate investigation of an outbreak in the Central African country of Gabon, scientists discovered that the species was the main agent for its spread. Whether the species would be as efficient a vector in transmitting Zika here is still under study.
The convergence of factors “is absolutely concerning,” said Ary Faraji, assistant manager of the Salt Lake City Mosquito Abatement District.
Such mosquito control agencies have sprung up in the past century to combat periodic salt-marsh mosquito infestations caused by tidal or storm flooding, or to address serious public health emergencies linked to yellow fever, malaria and other outbreaks.
Countering the Asian tiger mosquito is far more difficult because the insect evolved to raise its larval young in tiny pockets of water. In the jungle, that might be rain trapped in a bromeliad flower. In home gardens, that’s wheelbarrows, pots, watering cans, rain barrels, trash cans, birdbaths, clogged gutters, folds in tarpaulins, paddling pools, children’s toys, play sets, trash, soda cans and even bottle caps.
When I walk through my neighborhood or community garden, the array of potential breeding sites is truly astonishing. In one garden, plastic sheeting laid to solarize weeds had become perfect basins for mosquito larvae, which can develop into adults in a week.
“There’s isn’t a single mosquito control program in our nation that could have the resources to go through every single back yard,” Faraji said. He was a member of a Rutgers University team that spent five years studying the effectiveness of control strategies in urban Mercer and suburban Monmouth counties, in New Jersey, an area that includes Trenton.
In some districts, volunteers would survey and remove tires and drain containers, apply larvicides to standing water, spray pesticides to knock down adult mosquitoes, and, most effectively, bring education programs to neighborhood and schools.
In poorer, urban areas, residents were generally welcoming of the intervention. In the suburban districts, not so much, and about 30 percent of the homeowners wouldn’t participate, Faraji said. “There’s a lot of anti-government feeling out there,” he said.
In many yards where residents were cooperative, they were happy to have the containers cleaned up, but the problem would come back. “Even after they were aware which containers would be producing mosquitoes, they wouldn’t clean up their yard,” he said.
Spraying against adult populations is of little value if you don’t fix the sources of standing water, which form the engine of mosquito production. Applying insecticidal barrier sprays, a tactic of many pest control companies, won’t address the larvae issue and seems ecologically unsound. How many beneficial insects would you kill?
Another Rutgers study showed that if you identified and wiped out mosquito hot spots early in the season, you could make a significant reduction in their annual populations. “It really does work,” said Dina Fonseca, a professor of entomology at Rutgers. “July 27 is our magic date in Trenton. The population gets so big after that date” that you can’t reel it back.
The key is to get a whole community focused on cleaning up breeding sources, she said. “You have to engage the community ,” she said. “If you remove the containers from the back yard, [tiger] mosquitoes won’t have a place to live.”
Patterson, a professor of history at the Florida Institute of Technology, said that when he looked at records of Floridians who died of Saint Louis encephalitis, another mosquito-borne disease, he found the case of “a fellow who went out and gardened after work, and the mosquito got him and he died.”
The response may be to retreat from the garden, but that would be no fun. And cowering indoors in high summer seems fundamentally wrong. A way of life that removes us from the outdoors tends to make us even more indifferent to our effects upon it.
So for this growing season, I’ll be doing what I’ve been doing for a while, but with more diligence — making sure there are no vessels that hold water, wearing light-colored and long cotton clothing and a hat, and using repellents. My community garden plot might have enough citronella candles that it will look and smell like a shrine. Well, it is a shrine, and no mosquito is going to chase me from it.
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