Plenty of mosquitoes so far, but not West Nile variety

Jul 9, 2017 By Katie Roenigk, Staff Writer

As spring flood waters have receded throughout Fremont County, they have left behind pools of water that have become prime breeding grounds for mosquitoes -- and the accompanying human health risks.

Most of the buzzing bugs that have emerged so far are not the type that can carry the dreaded West Nile virus, however.

"Those are floodwater mosquitoes," Fremont County Weed and Pest assistant supervisor Nancy Pieropan said Friday. "The mosquitoes we're seeing now are not transmitters of West Nile."

No culex

Culex tarsalis is the only species of mosquito that carries West Nile, and Pieropan said "very few" of those have been identified in traps so far this season.

None of the culex identified have tested positive for West Nile, either.

That doesn't mean the traps have been empty, though. Pieropan said she saw bigger bug numbers than usual when the trapping program began in June.

"The numbers are higher than they were last year certainly, by a couple hundred in some areas," she said, reiterating, "We've had some very high numbers - but very low numbers of culex tarsalis."

Slow start

Her earliest data for 2017 came June 6 in Hudson and Lander, where numbers were still low.

On that day, the trap on Carbine Lane in Lander held 168 mosquitoes, including 17 culex, and on Cascade Street there were five mosquitoes, with one culex.

On June 6 on Ohio Avenue in Hudson there were 52 mosquitoes including 37 culex, and outside of Hudson on Snavely Lane there were 225 total and three culex.

One week later, on June 13, the numbers had gone down.

A trap monitored on Left Hand Ditch Road south of Riverton contained only two mosquitoes with no culex, the Carbine Lane trap was empty, and there were only four mosquitoes, including one culex bug, in the trap on Ohio Lane in Hudson.

Riverton numbers

Riverton traps, which were monitored for the first time June 14, were pretty sparse as well, with two bugs on Davis Lane, two on Sunset Drive and seven on Smith Road. Only one culex tarsalis mosquito was identified that day, on Smith Road.

On June 15, six traps combined in Lander produced 47 mosquitoes, including seven culex.

More in June

Later in the month, there was a mosquito population boom.

On June 20, 1,900 mosquitoes were trapped on Left Hand Ditch Road (three culex) and 2,200 were on Snavely Lane (two culex).

There were 305 mosquitoes in the trap on North Smith Road (25 culex), 260 mosquitoes in the trap on Carbine Lane in Lander (six culex), 138 mosquitoes on Ohio Avenue in Hudson (two culex), 58 mosquitoes on Sunset Drive in Riverton (no culex) and 20 on Davis Lane in Riverton (no culex).

On June 21, three traps in Lander contained 402 mosquitoes and seven culex altogether.

Totals remained high at the end of June, with 4,500 mosquitoes in the Left Hand Ditch Road container June 27, but only five culex; 1,950 on Snavely Lane, with only seven culex; and 1,525 on North Smith Road in Riverton, but only five culex.

That same day, Lander's Carbine Lane trap had 620 mosquitoes and 15 culex, Ohio Avenue in Hudson had 35 mosquitoes and 18 culex, Davis Lane in Riverton had 295 mosquitoes and eight culex, and Sunset Drive in Riverton had 60 mosquitoes and one culex.

Five traps in Lander held a total of 150 mosquitoes June 29


On Thursday, Pieropan sent out an email indicating numbers had fallen this week.

"They're going down now," she said. "The numbers went down considerably, which is really good news."

There are still "extremely high" numbers of mosquitoes on Snavely Lane and in Arapahoe, she noted, but again, not many culex.

On Left Hand Ditch Road there were 1,700 mosquitoes with 33 culex July 6. On the same day there were 1,750 mosquitoes in the trap on Sanvely Lane, including eight culex.

The Carbine Lane trap in Lander held 168 mosquitoes and eight culex July 6, and Hudson's Ohio Avenue trap had 46 mosquitoes and 17 culex.

July 6 in Riverton revealed 536 mosquitoes on North Smith Road, including 26 culex; 242 mosquitoes on Davis Lane, including four culex; and 22 mosquitoes on Sunset Drive, including two culex.

Spraying works

The numbers show the difference between areas that are controlled by mosquito spray programs and those that are not, Pieropan noted.

Totals on Snavely Lane, Left Hand Ditch Road and, to a lesser extent, North Smith Road in Riverton, are consistently higher than those within Fremont County municipalities where workers regularly spray mosquito repellant throughout town.

Without the spray treatment, Pieropan said local cities would have many more bugs.

"Lander would be terrible," she said. "We're surrounded by irrigated fields. But we have a control program, so it's not as bad."

Her agency is not able to provide assistance for private landowners looking to repel mosquitoes from their properties - "We just don't have the budget," Pieropan said - but Weed and Pest does offer cost sharing for larvacidal chemicals that can be applied to standing water before mosquitoes emerge.

Be prepared

The best way to avoid West Nile, she said, is to make sure screens are secure, wear bug spray, avoid being outside at dusk and dawn, wear long sleeves and light colors, and drain any standing water that might be attractive to culex tarsalis mosquitoes.

The species doesn't like flood water, Pieropan explained, but culex do enjoy stagnant liquid that pools in containers like boats, gutters, tires and dog dishes.

"Get rid of standing water around your house - that's where mosquitoes breed and larva are," she said. "Look around your own area to make sure you're not creating the habitat (they like)."

The West Nile mosquitoes are currently busy feeding on birds, which are the carriers of the virus, Pieropan continued, but once the majority of bird chicks have fledged, she said the culex tarsalis will turn their attention to mammals.

West Nile also requires high temperatures to amplify inside of the mosquito, she pointed out, so it is more likely to emerge as the weather warms.

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