Mosquitoes with West Nile virus detected in Montana

Despite the drought, mosquitoes are still finding a way to persist, including the species that carry diseases like West Nile Virus, and the Hill County Mosquito Control District reported Sunday that mosquitoes testing positive for West Nile were found in northeastern Montana.

Hill County Mosquito District Supervisor Terry Turner said mosquito samples are collected once a week and sent to Carroll College where students analyze the sample pool for total number of mosquitoes and numbers of each species present along with the number of mosquitoes, if any, that test positive for diseases, which can include West Nile virus and western equine encephalitis. He added that they have tried to keep the trap in the same general location to get a consistent read on long-term numbers.

Hill County district numbers have been low this year, Turner said, much different from the 4,000 mosquitoes per sample pool taken at the start of the district in 2004, when West Nile first hit the U.S.

Sampling this year started July 7 and the district reported collecting only 88 mosquitoes that day, three of which were target species that carry disease, and all were negative for West Nile Virus. By July 28, 158 mosquitoes were trapped, but nearly 70% were of species that have potential to carry disease. They all tested negative for West Nile. And no traps in the state at that time had a positive test.

However, the release Sunday said West Nile virus was found in two mosquito sample pools near Medicine Lake in Sheridan County, which is the northeastern corner of Montana. Of the 1,728 mosquitoes 83% were of the species that can carry disease.

Turner said that as of Tuesday morning, those results remain the only positive tests in the state.

By comparison, the last test sample in Havre had a total of 348 mosquitoes with 60 being a disease carrying species, and all tested negative for disease, the release Sunday said, but a trap in Central Montana had 5,174 mosquitoes; another had 1,606; and another had 1,389.

"There's just little hot spots of (mosquitoes) and there's not a big bunch as usual," Turner said, adding that any time the sample collection is fewer than 250 is good.

Some of the increase in mosquito numbers in the Hill County district is related to recent high humidity and the hot spots are due to irrigators pulling the last water from the Milk River for the season and some is due to people over-watering their lawns.

Hill and neighboring counties have about 14 species of mosquitoes, out of 52 identified in the state, Turner said.

Late July and August is when the mosquitoes carrying disease show up in the state, Turner said, generally starting on the eastern border and moving west.

Heat will create conditions that rapidly increase mosquito populations, shortening the mosquitoes' incubation period, but they also have to have water to breed in and rains from the last 24 hours and those predicted this week could bring a rapid increase in mosquito numbers.

Turner said that one cup of water can produce up to 250 mosquitoes and a 5 gallon bucket that is half full can produce up to 10,000. Standing bodies of water around an acre in size could produce billions of mosquitoes, he said, adding that mosquitoes do not breed in running water.

Many of the mosquito species only travel about a mile at the most, although some can travel up to 15 to 30 miles, Turner said. High winds, but, can also blow mosquitoes in from as far away as Rudyard, so the moisture doesn't have to be coming from the immediate area.

The Hill County Mosquito Control District covers Havre to 6 miles south, 7 miles north, 7 west and then to Blaine County line. The Hill County district is divided into eight zones, Turner said, and the crews try to fog them all once a week, but the wind has to be below about 14 mph or it drives the fog down to the ground where it is ineffective against the mosquitoes.

While the fogger can help deplete adult mosquito populations, one of the keys for mosquito control is to eliminate their breeding grounds.

Turner and the American Mosquito Control Association recommend:

• Disposing of tires and other clutter that can hold even small amounts of water.

• Clearing roof gutters of debris.

• Checking and emptying things like children's toys, buckets, barrels, lids, tarps, swimming pool and barbecue covers, or other items that can hold even small amounts of water.

• Regularly dumping out outside pet waterers and bird baths.

• Not over-watering lawns.

• Repairing leaky outdoor faucets.

• Turning over canoes and other boats.

• Keeping lids on or drilling holes in the bottom of garbage and recycling containers.

• Filling ruts, holes and depressions where water pools.

• Using mosquito larvicide pellets in areas where standing water can't be avoided. The pellets are safe for humans, pets and plants, but they prevent mosquito larvae from hatching into adult mosquitoes.

Culex tarsalis, the species that carries West Nile virus and western equine encephalitis, is a black mosquito identifiable by a white band on its proboscis, as well as white bands on its tarsal joints.

Turner said Culex tarsalis tend to be night-time mosquitoes in the area, so along with avoiding being outside at dawn and dusk, when mosquitoes are most likely to be feeding, to help avoid being bitten Turner and AMCA recommend:

• Apply a mosquito repellent when outside: DEET, picaridin, IR 3535 or oil of lemon-eucalyptus. Picaridin, Turner said, is safe for infants and pregnant women.

• Wear long sleeves, long pants, and light-colored, loose-fitting clothing.

Turner said the mosquito district larvicide pellets are available free at Havre Hardware and Home, Ezzie's Wholesale and at the Hill County Weed District office, 1405 Second St. W., and Stromberg's Sinclair is selling picardin repellents.