Oswego County Legislature Chairman's Office, 46 East Bridge St., Oswego, NY 13126

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Aug. 31, 2006

Why Did We Spray for Mosquitoes?

Over the past few weeks we’ve heard and seen many news bulletins about aerial spraying for mosquitoes. Some people have wondered why it is necessary to spray for mosquitoes, and others have asked why we don’t spray every year. In short, the Oswego County Health Department sprays for mosquitoes when surveillance shows that Eastern equine encephalitis, or EEE, is a threat to human health.

The shores of Oneida Lake provide a perfect breeding area for some types of mosquitoes, including the primary carrier of EEE virus, Culiseta melanura. The EEE virus is transmitted by infected mosquitoes to birds and mammals. Although it is rare in humans, EEE is one of the most serious mosquito-borne diseases. It attacks the central nervous system of humans and horses, causing severe infections that frequently are fatal.

As part of an ongoing and long-term surveillance program, research scientists from the state Health Department collect samples of mosquitoes from sites near the village of Central Square and in Toad Harbor Swamp. These collections target the Culiseta melanura mosquito. The collections are identified, grouped by species, and sent to the state health department laboratory near Albany for testing for EEE virus.

In late July and early August, 36 groups of mosquitoes in Central New York counties tested positive for EEE virus. More than half of the isolations, 24, were collected from a site near the village of Central Square. There were two from the site in Toad Harbor Swamp, with eight from Onondaga County, and one each in Madison and Oneida counties.

The high number of virus isolations from Culiseta melanura mosquitoes near a populated area of Oswego County was felt to constitute a public health threat in Oswego County. For this reason, the county Health Department, in consultation with the state Health Department, decided it was necessary to conduct aerial spraying along the north shore of Oneida Lake. It’s been at least 15 years since Oswego County had to spray for EEE.

The county contracted with Duflo Spray-Chemical Inc. of Lowville to spray about 10,000 acres between the village of Central Square and the village of Constantia. The pesticide Kontrol, which contains permethrin, was sprayed over the area. The pesticide is applied according to state and federal environmental regulations and the operation is inspected by the DEC.

Pilot Jeff Duflo and his crew have done years of testing to find the smallest possible dosage and smallest possible droplet size that will control mosquitoes while they’re most active – around dusk when they are likely to be flying. The spray needs to penetrate the foliage and be large enough that it will make contact with mosquitoes when they’re in the air.

Jeff Duflo tells us that years ago, when he first started flying with his father, the pesticide was applied at a ratio of one pint per acre. Today, the company uses .36 ounce of permethrin, in an application of 1.75 ounce per acre of Kontrol, to kill mosquitoes. They use a system they pioneered themselves, diluted to a precise mixture, to be much more specific and much more friendly to the environment. The droplets are so fine that much of the pesticide has dissipated by the time the droplet hits the ground.

The aircraft is equipped with an advanced GPS system and software to map out the spraying area and flying routes. The spray is automatically turned off when the plane flies over environmentally se

nsitive areas. Specific areas that were avoided during the spraying of Toad Harbor Swamp were organic hayfields and a large heron rookery near state Route 49.

The county looks at several factors when it decides whether or not to spray. It’s not a decision that is made lightly. Besides the numbers and species of mosquitoes, factors such as weather conditions, infection rate, and the time of year are considered. The mosquito population will decrease gradually as the weather cools, and will drop dramatically once we’ve had one or two good frosts.

The best way to protect yourself against mosquitoes is to use insect repellants when you’re outdoors in mosquito-infested areas. Change the water in bird baths frequently and eliminate sources of standing water around your home. Wear light-colored clothing, and wear clothes that cover your arms and legs if you’re going to be outside around dawn and dusk, when mosquitoes are most active. However, when there is evidence of EEE virus near populated areas of Oswego County, it may be necessary to take the extraordinary step of conducting aerial spraying to control the mosquito population and protect the public health.

For more information about EEE, contact the county Health Department at 349-3557 or 1-800-596-3200, ext. 3557, or visit the state Health Department Web site at www.health.state.ny.us/diseases/communicable/eastern_equine_encephalitis.htm on the Internet.

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