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West Nile carriers already detected in city, expert says

May 22, 2012 - By Emily Etheredge, Staff Writer

Mosquitoes of the type that carry West Nile Virus already have been detected around Riverton this spring.

Riverton City Councilman Lars Baker gave his annual mosquito report at the end of the Riverton City Council meeting May 15, when he also reported on grasshopper conditions.

Baker who also is supervisor of the Fremont County Weed and Pest Control District, said he trapped two mosquitoes in the city last week that were Culex tarsalis, the prime carrier of West Nile virus.

"We have had cases in the state of Wyoming where people contracted West Nile during the month of May," Baker said. "A word to the wise is if you are out and about on these warm evenings, you need to be aware that mosquitoes are out. They slip up on you when you are not paying attention to what is going on."

In a follow-up interview, Baker said the weed and pest district runs a mosquito monitoring program with more than 20 mosquito traps throughout the county.

Baker said mosquitoes are trapped on a weekly basis, with some of the traps set up in the city and some outside city limits.

"It is actually a pretty dramatic difference with 3,000-4,000 mosquitoes in our traps down on the river east of Riverton, where there is no fogging," Baker said. "In the city limits you can get about five or six mosquitoes, so the fogging program is about 99.9 percent effective in reducing the number of mosquitoes."

Baker said mosquitoes appear typically when the weather warms up. The ones making their debut this month have been hiding out in the storm drains where it rarely freezes during the winter.

"The mosquitoes showing up right now fed on flower nectar last summer, so they had sugar in their systems --storing it up for the winter," Baker said. "When things warm up, they come out and start looking for a blood meal."

Baker said with an average daily temperature of 65 degrees it takes 21 days for West Nile to incubate in a mosquito. When the temperature is raised to 75 degrees, it only takes five days for the West Nile virus to incubate.

"Wyoming has a perfect vector for the West Nile virus," Baker said. "Even though the weather is really dry this year, and the mosquito population will be down, I would not be surprised to see a number of infected cases."


Baker also addressed grasshoppers during the council meeting, with warnings that they are emerging now. Typically, grasshoppers do not make their appearance until mid- June but are at the cusp of hatching due to the warmer weather now.

"The general indicator for grasshoppers hatching is when the iris blooms, and we are seeing iris pop up around town," Baker said. "Grasshoppers are worse in drought conditions, and if this were a hurricane or tornado warning I would be making my announcement."

Baker said the grasshoppers are worse in Lander, but no one has the explanation for why that is.

"It is an age-old mystery no one has ever been able to figure out," Baker said.

Baker said residents in Lander will struggle with their gardens this year due to looking at grasshoppers in abundance of 100 per square yard. Grasshoppers are plant-eating insects.

"Right now the grasshoppers are as small as a grain of rice," Baker said. "Some of the grasshoppers appear when the lilacs start to bloom. The lilacs are gone now, so we probably missed a hatch of them because they never showed up. We are really only dealing with one species so far."

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