Methods help rein in mosquitoes

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While some towns spray, Bartonville and others opt to control just larvae

So far, Bartonville has managed to avoid any West Nile virus infections, even though the town of 1,600 is surrounded by areas that have reported cases of the disease and mosquitoes found to be carrying it.

For at least five years, the town hasn’t had any reported cases of West Nile, a feat Mayor Ron Robertson is hesitant to attribute to the town’s use of a product that attacks mosquito larvae.

The town uses Mosquito Dunks, doughnut-shaped tablets that float in water that prevent mosquitoes from reproducing.

“I use them in my water tanks, too. … They have to be added to water about twice a year during mosquito season,” Robertson said. “We use them around early spring, before mosquitoes begin reproducing.”

The dunks contain Bacillus thuringiensis israelensis, or BTI, a bacterium that kills mosquito larvae in standing water, with only minimal, if any, effect on water quality, said James Kennedy, a University of North Texas biology professor.

Though Robertson isn’t sure the dunks are the best solution, they’re inexpensive and seem to be working.

Bartonville gives away the tablets to residents. Robertson said the town has spent less than $1,000 in the last two years on the mosquito control product, a cheaper alternative to the chemical sprays that many cities use to control mosquitoes.

Robertson said a spray rig would cost about $15,000, not including the hourly expenses for a town staff member to operate it. He also noted that the spray eliminates only adult mosquitoes.

But is BTI more effective than mosquito spray?

“The quick and short answer is yes,” Kennedy said. “Attacking the larval habitat is a very effective method of mosquito control.”

Kennedy said the fight against mosquitoes is dependent on the residents of a community.

“The public awareness that the current round of [West Nile] has generated is good because people now understand the importance of taking precautions to minimize contact with mosquitoes,” he said.

Residents can prevent the spread of mosquitoes by eliminating standing water and regularly changing water in pet dishes, he said.

“A discarded soft drink can that fills with water from a lawn sprinkler system can produce a new generation of mosquitoes in a matter of days,” Kennedy said. “Spraying can have a knock-down impact on mosquito populations, but unless the mosquito larvae are eliminated, it only takes a few days to build populations back to pre-spray conditions.”

The Sanger City Council elevated the city’s mosquito risk level after a human case of West Nile virus was confirmed in the county. Sanger sprayed for mosquitoes July 23, and city officials expect spraying to continue if the virus continues to be a threat.

Lewisville, Flower Mound and the Lake Cities communities have also used spraying to control the mosquito population.

Another round of spraying has been scheduled for Wednesday night into Thursday in western Denton. This time, the spray truck will follow a route around homes on Lariat and Hampton roads.

The city’s environmental director, Ken Banks, said the city will continue to take action based on 10 years of tracking both mosquito pools and human cases, which tend to peak in Denton in September.

“Whether that happens this year or not, we will keep undertaking action as if that is the case,” Banks said. “It’s been a very unusual year.”

A total of 29 cases of the disease were confirmed by Denton County health officials in July. Seven cases were confirmed in the first three days of August. The latest confirmed cases include one in Corinth, three in the city of Denton and one in the unincorporated part of the county near Sanger. As of Friday, the county had confirmed 49 cases for 2012.

Thirty of those cases were diagnosed as West Nile fever. Another 19 were diagnosed as the more serious West Nile neuro-invasive disease.

No deaths attributed to the virus have been reported in the county for 2012. At least five deaths in Dallas County and one each in Travis, Tarrant and McLennan counties have been attributed to the virus.

So far, Denton County reports that samples taken from 61 locations have tested positive for the virus. UNT, under a contract with Denton, sets mosquito traps weekly to test for the presence of West Nile and other mosquito-borne illnesses inside the city. Flower Mound and Lewisville also test for mosquitoes and report positive mosquito pools to the county.

JOHN D. HARDEN can be reached at 940-566-6882. His e-mail address is jharden@dentonrc.com.

PEGGY HEINKEL-WOLFE can be reached at 940-566-6881. Her e-mail address is pheinkel-wolfe@dentonrc.com.


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