Not enough mosquitoes for spraying in Cumberland County


CARLISLE, Pa. (WHTM) — Despite national concerns over Zika virus, mosquitoes aren’t making much of an impact in the Midstate this season.

Already nearing the end of the traditional “mosquito season” occurring between April and mid-September, technicians with Cumberland County Vector Control are reporting fewer bugs in traps this year. Additionally, the number of mosquitoes infected with West Nile virus is currently less than half of the 2015 total.

“Right now, we have 46 positives,” said Katie Seymore, a West Nile technician with Cumberland County. “Last year, it was 95.”

Seymore, who routinely sets and collects mosquito specimens from roughly 30 traps across the county each week, says numbers are at a cyclical low. Since Pennsylvania began West Nile surveillance in 2002, there have been peaks and valleys in mosquito populations and presence of the virus. The most recent high point in 2012 has gradually slowed to a point that presents only a minimal threat to public health in 2016.

As of Tuesday, only seven human cases of West Nile Virus had been reported in Pennsylvania, including one case each in Lebanon and York counties. Last year, 30 human cases were reported statewide.

In Cumberland County, mosquito numbers have been so low this year, specimen collections have yet to meet state requirements for initiating evening spraying programs. For the county, it means a new $13,000 piece of spraying equipment purchased this year has yet to be used in the field. It sits idle in the back of a large pickup truck.

“It has LED lights in the back and it’s very quiet,” Seymore said. “It puts out an ultra-low volume spray. It’s very cool, and we have been excited to use it, and we just haven’t been able to.”

While keeping the new equipment sitting could be considered a positive, there is still potential for use this season. With temperatures holding steady in the mid 80’s in late September, mosquitoes are still actively breeding wherever they can find habitat, such as in shallow retention ponds, bird baths and inside old tires containing water.

While evening spraying may not be warranted, Seymore says she and other staff members remain busy by treating those breeding habitats with topical larvicide. The practice of sprinkling small pellets of the organic treatment into stagnant water has tripled this year over last, targeting areas where large populations of mosquitoes have been trapped or West Nile virus detected.

“We put that product into the water and it basically eats the mosquito from the inside out,” said Seymore, who added the active ingredient poses no threat to people, pets or wildlife.

While dry summer weather may play a factor, Seymore believes two other factors account for the low mosquito numbers and West Nile cases this year. Immunity to the virus could be particularly high in birds this year, another cyclical factor that could just as easily change drastically by next spring. Additionally, she believes the national media attention pertaining to Zika, while unlikely to affect the Midstate, has heightened public awareness.

“People are more vigilant about their backyards and habitats,” she said. “That might have helped decrease the mosquito population. We just haven’t had the numbers we’ve had in the past.”

Because of federal grants for the study of Zika virus, Cumberland County Vector Control will continue to trap and monitor mosquitoes through the end of October, weather permitting.

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