By Barbara Kessler
Green Right Now
Mosquito season generally runs heaviest from June to August, but tell that to the mosquito that bit you last night while you were trimming the first May-blooming roses.
In many parts of the U.S., that first bite brings a sense of dread, because residents are well aware that mosquitoes can carry West Nile Virus, an illness that is generally mild, but can, in rare cases, cause a serious, sometimes fatal encephalitic response.
West Nile was especially devastating in 2012 in Texas, where 1,739 people were reported as becoming ill with the disease and 76 died, according to the Centers for Disease Control. It was the worst outbreak in the nation, with most cases concentrated in the Dallas/Fort Worth metro area. It so spooked Dallas officials that the city authorized aerial spraying in selected areas for the first time since the 1960s, and understandably — people were dying.
Cities and individuals have been fighting West Nile Virus in the U.S. since it arrived officially in 1999. Several cities and counties have gone full-bore with insecticides, dousing affected neighborhoods by airplanes or with fogging trucks. But this practice is controversial. People have reported that the insecticides sprayed — generally synthetic pyrethroids which kill adult mosquitoes on contact — have killed bees and depressed butterfly and bird populations as well. On the other hand, the insecticide camp promises that the chemicals used are a)effective and b)biodegrade in sunlight starting the next day.
Sometimes, people report birds dying in the middle of the West Nile outbreak, which adds to the angst over spraying. But this may or may not be an outcome of spraying, say experts. The birds, which carry West Nile, may be succumbing to the virus itself itself. So the presence of sick birds simply adds a layer to the conundrum over spraying, which could harm the birds; on the other hand, sick birds indicate the virus is present in the neighborhood, and being transmitted to mosquitoes, which in turn infect humans.
To Spray or Not-to-Spray
All this debate leads to the perennial question that dogs the dawn of summer: What is the most effective method to fight West Nile Virus? Those who study the problem bring a little clarity. They agree that the very best first line of attack is to try to keep mosquitoes from breeding near your house, and to use repellents (see more below) to avoid getting bitten.
But beyond those steps, even the experts wonder about the best tactics.
“It’s not really clear what’s the best way to combat these West Nile outbreaks,” says Michel Slotman, a professor of entymology at Texas A&M University. ”The spraying obviously has some impact, or probably has…the data isn’t really very clear.”
The data isn’t clear? Yes, you heard Dr. Slotman right. While opponents of aerial spraying swear that it’s not effective at all, and those who endorse it, claim that it stamps out adult mosquito populations, the scientific evidence, at least as interpreted by some scientists, remains inconclusive.
Because mosquito populations are notoriously difficult to measure, Slotman, among others, say that it’s difficult to nail down the effectiveness of aerial spraying. For similar reasons, it’s also difficult to determine how damaging the spraying is to other wildlife in the spray zone.
So you end up with the two cities at ground zero in last year’s outbreak following different paths. Dallas elected to spray during the epidemic of West Nile Virus in 2012, and Fort Worth held its ground on not spraying. Dallas officials declared the spraying to have squelched 90 percent + of the mosquitoes in target areas. Fort Worth dismisses spraying as ineffective, and causing collateral environmental damage.
As for the collateral damage, Slotman admits that some birds do show ill effects, though others seem impervious to spraying. They react differently across subspecies, just as their susceptibility to West Nile seems to vary, with crows and blue jays for instance showing more vulnerability, he said. The effects on butterflies, bees and other beneficial insects remains largely a mystery.
A study by A&M researchers in 2012 that gathered feedback from 75 Dallas residents living in sprayed areas found that some people reported “dramatic changes” to their local ecosystem while others saw no discernible effect on backyard butterflies, bees, dragonflies, fish and chickens.
One respondent reported an 80 percent drop in the dragon flies observed in his/her yard, while another said: “I was pleased to see butterflies and bees the very next day. I found no dead butterflies at all and I have a garden primarily for butterflies and birds.” Respondents with fish ponds reported no ill effects.
The widely varying comments could be a result of the residents preconceived notions about spraying, or the result of an admittedly imprecise process, the researchers wrote.
Was the lack of damage to other wildlife evidence that spraying is largely safe, or that it is ineffective, failing to break through tree canopies or missing the target insect? We may not know for many years.
As the debate continues, Slotman says his view is that spraying “is probably better than doing nothing” because it can kill the Culex mosquito that carries West Nile Virus. But in the absence of strong studies on the practice and outcomes, “people shouldn’t assume that once we send a spraying plane over it, the problem’s solved,” he said.
Prevention = Protection
The most important way to reduce your odds of contracting West Nile is to take action in your own environment, he said. First, keep mosquitoes from breeding in your yard, and second (or maybe first), keep them off of you.
Mosquitoes don’t travel far, and that’s a strategic advantage that humans can leverage, Slotman says. Remove all standing water from in and around your yard. Dump out flower pot basins, fill divots, patrol for places water collects, inspect your rain gutters and refresh bird baths frequently, and even better, use mosquito “dunks” in your bird baths and ponds.
The Centers for Disease Control has more advice on a new webpage about eliminating mosquito habitats. Both the CDC and Slotman advise that neighborhood associations should band together to identify and eradicate mosquito breeding grounds.
Dunks, which a naturally occurring bacteria that occurs in nature and won’t harm birds, can be used in neighborhood ponds and water features. Mosquito larvae cannot tolerate the bacteria and will be killed before they hatch. This natural solution can thwart the mosquitoes that are near year house, thereby reducing the numbers that show up for dinner on your arm, and your chances of contracting West Nile. It also stops mosquito populations from multiplying, tamping down on their overall numbers.
Since only about 1 percent of mosquitoes carry the virus, and only 1 in 150 people who contract it will develop life-threatening symptoms, your odds are good, but these proactive measures make them even better, Slotman said.
And of course, be vigilant when mosquitoes are most active, at dawn, dusk and at night, because keeping them off of you and yours is the next line of defense.
Fortunately, the array of effective repellents has broadened in recent years, so you’re not necessarily stuck with the old standby, DEET. The Centers for Disease Control’s latest advise on DEET is that it is effective against mosquitoes and offers some of the most enduring protection. However, the CDC also endorses other ingredients as effective, including some botanicals. Some of these, however, may need to be reapplied more often. Here’s the full list from the EPA, with links to product information:
- DEET — This chemical has been proven effective against mosquitoes, though you don’t have to use the 25 percent or 40 percent formulas. DEET products are available in 7 percent solutions, and they’re just as effective, Slotman says. The higher the percentages simply prolong the time the repellant works. The problem with DEET is that some people don’t like applying such a harsh chemical. Fortunately, CDC testing found more options that are effective.
- Oil of Lemon Eucalyptus — This natural, essential oil has become the ingredient in a host of commercial and homemade repellants (see the recipe below). Be aware, just because something occurs in nature, doesn’t mean it cannot cause a skin or allergic reaction. You’ll have to try it to see.
- Picaridin – This is a synthetic that is part of the piperidine family of compounds, based on the extract from plants used to make black pepper. Applied to clothing, picaridin deters insects from feeding or biting. It’s considered safe for use on the skin, and is sold in repellent solutions in 20 percent strength.
- IR3535 — This CDC-approved repellent is often overlooked (perhaps the numerical name is not so catchy). But you know it if you’re familiar with Avon’s Skin-So-Soft products. Avon’s been making a killing on this line since people discovered it really works. It was an early replacement for DEET, which had been found to produce allergic and neurological side effects in sensitive individuals (the manufacturer has said these rare reactions may have been the result of overuse or misuse). In any event, the Avon products are considered non-toxic, and safe for kids. Bullfrog and other brands are also using this ingredient in repellents.
- Catnip Oil – This botanical oil from the herb by the same name (more properly known as refined oil of Nepeta Cataria) offers 7 to 15 hours of protection, depending on the concentration (7 percent or 15 percent). It can be found in a variety of botanical repellents on the market, and is sometimes combined with other essential oils, such as oils of geranium, citronella and lemon grass.
- p-Menthane-3,8-diol — This “biologicial” pesticide is a synthetic made to mimic the naturally occurring compound found in lemon eucalyptus plants. It repels flies and gnats, as well as mosquitoes.
These are the recommended and tested ways of keeping mosquitoes at bay (the ingredients above have all be registered by the EPA, which may or may not prove comforting to you), but they’re by no means the only formulas available. Homemade repellents intended for use on the skin and other deterrents abound on the Internet. Some use the botanicals mentioned above. More to come on that in our next installment.
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