No shortage of mosquitoes

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A female mosquito draws blood from a hand Tuesday in Jamestown. John M. Steiner The Sun

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Steve Reidburn, Jamestown vector control officer, has noticed the increase in mosquito numbers like everyone else.

“They’re bad,” he said. “We saw about a 200 percent increase in the traps about the 23rd or 24th of July. That is about the time things started getting wet and warm.”

And wet and warm weather makes for a lot of mosquitoes, including the kind that carries the West Nile virus.

“As the temperatures of standing water warm the mosquito life cycle shortens,” said Michelle Feist, West Nile virus surveillance coordinator for the North Dakota Department of Health. “As the length of a generation of mosquitoes shortens the count increases.”

With a short life cycle now, sometimes approaching just a few days, Reidburn said mosquitoes are laying eggs, hatching into larva and growing to adulthood in the many temporary ponds of water standing after recent rains.

“The standing water is not evaporating,” he said. “Prior to this summer it was but after the last rains it isn’t. Those puddles that used to dry up but now have standing water are excellent habitat for mosquitoes.”

Complicating matters is the species of mosquito now emerging.

“The culex tarsalis mosquito numbers are increasing,” Feist said. “They are the ones that can carry the West Nile virus. They usually peak at the end of July and early August and that is when we see a peak in cases of the human illness as well.”

Two cases of West Nile Virus have been confirmed in North Dakota this summer. The virus was first identified in the U.S. in 1999 and in North Dakota in 2002. A person becomes exposed to the disease when bitten by a mosquito that has previously bitten an infected bird, horse or human. Feist said about 80 percent of the people exposed to West Nile virus develop no symptoms but do have immunity to the disease in the future.

Reidburn describes culex tarsalis mosquitoes as “small, fast and vicious,” and said they currently amount to about 30 percent of the mosquitoes trapped in Jamestown.

For Reidburn and his one assistant, the surge in the number of mosquitoes has meant long hours. They continue to spread larvicide — chemicals placed in standing water to kill the larvae stage of the mosquito — and spray to kill the adults. Citywide spraying is done anytime the number of female mosquitoes in the nine traps around the city averages 125. Prior to the wet weather mosquito averages were between 35 and 38 insects per trap. Since the wet weather the maximum has been 258 mosquitoes per trap. Trap numbers on the days after spraying have been between 60 and 90 mosquitoes.

“Right now we’re spraying citywide every other or every third night,” he said. “We spray parks and places people gather every night weather allows.”

Reidburn said the cost of the chemical for a citywide spray effort exceeds $2,000. The vector control department budget is funded by a $1 per month surcharge on Jamestown water bills.

Along with his efforts Reidburn would like to see residents do what they can to eliminate the breeding sites in their yards.

“The average person needs to keep their grass mowed because they like tall grass,” he said. “Dump bird baths and wading pools every day or so. Eliminate anything that is holding water unnecessarily like rain gutters or even low spots in yards with setting water.”

Residents should also dress in long-sleeved shirts and pants rather than shorts when outside, especially during the prime mosquito times of dawn and dusk. Using mosquito repellants also can reduce the number of bites. However, at this time Reidburn and Feist recognize that high mosquito numbers may continue until weather conditions dry enough to limit breeding sites.

“The trends are the same across North Dakota but the magnitude varies with the region,” Feist said. “Larvicides and other efforts can reduce the population but you’re never going to reach every place. We can never eliminate the risk because mosquitoes can fly for miles.”

Sun reporter Keith Norman can be reached at (701) 952-8452 or by e-mail at knorman@jamestownsun.com

Tags: local news, news, mosquito