As of Oct. 12 this year, 47 more mosquito pools have tested positive for West Nile virus in Frisco than in 2015.

From the time the city began testing mosquito pools in May, the communications office has sent nearly weekly notifications about positive results and weekend mosquito spraying, leading residents to express concern at the city’s town hall meetings and through other outlets.

However, one of the main reasons behind the influx of positive results is not because of a worse mosquito season but because of an increased effort by the city to test more mosquito pools than in previous years, said Julie Stallcup, Frisco’s environmental health supervisor.

“We really need to expand our trap site locations to better serve [residents] and adequately get a picture of what the mosquitoes are doing around the city,” Stallcup said.

The increase in trap sites is due to the increase in development and population numbers, Stallcup said.

No human cases of West Nile virus have been confirmed this year in Frisco.

In an effort to better control the mosquito population this year, the city changed its strategy by increasing the number of mosquito pool testing sites.

“We have a much better response time so we can really figure out how to tackle the issue and hopefully really get it down before we allowed the chance for the disease to spread,” said Erin Plaisance, Municipal Mosquito laboratory supervisor.

Increase in positive pools

Municipal Mosquito has worked with the city since 2010 to set up traps and spray the area when positive results called for it.

“With the increased number of trap sites you notice more positive counts,” Plaisance said. “So we’ve seen more positive trap sites this year, but it’s because we’ve doubled the number of site locations.”

Plaisance said the reason to increase the number of trap sites was to figure out exactly where the disease is within the city.

“If you [test] in just a small range, you’re still forgetting the rest of the city, and Frisco is such a developing city,” Plaisance said. “With everything going on you want to make sure you can service all of your residents—not just a small portion.”

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Last year, Frisco had only six areas with positive pools, but the trap sites were located in less areas of the city. This year, 15 areas reported positive pools, but traps were located throughout the city.

Patrick Prather, an entomologist and president of Municipal Mosquito, said though the increase in trap sites contributes to the higher number of positive cases, a number of other factors can also contribute to the higher number.

Prather said he works with a lot of cities that in one year will have a high number of positives and then a low number the following year.

“It’s really a combination of factors on a moving spectrum,” Prather said. “It’s really a matter of how the virus is traveling and what’s going on in the city. This season it’s just Frisco’s turn to be the hot spot.”

Population control

Municipal Mosquito set up most of the trap sites in areas near rivers and streams or where construction is occurring, which Plaisance said could increase mosquito activity, because when crews move dirt around, they can create pockets that hold water.

Studies show that female mosquitoes prefer to lay eggs in standing water, which Municipal Mosquito will treat with larvicide to prevent mosquito eggs, larvae or pupae from developing.

As an additional treatment step, Municipal Mosquito will conduct ground-based adult mosquito control, known as fogging and spraying, in the targeted areas by using organic solutions.

Outside of the contract dates with Municipal Mosquito, Stallcup said city staff is always prepared with larvicide year-round to prevent mosquito activity in case of bad weather.

In some areas, Municipal Mosquito has sprayed multiple times to try to contain the population so those numbers do not increase, Plaisance said.

“Unfortunately some cities surrounding Frisco may see a positive pool, and they may not spray or they may fog just a small portion of the tract rather than the entire area,” she said. “And because some cities are still sending their pools to Austin for testing, their results are coming in later, and by that time any positive mosquitoes will have probably moved on.”

Plaisance said some cities surrounding Frisco do not have a protocol to control mosquito populations.

“If you allow the mosquitoes to amplify in count, that’s amplifying the [positive results], so it’s really a Catch-22,” she said. “So we’re trying to figure out how to service Frisco best.”

Plaisance said increases in positive results have also been caused by weather patterns that brought heavy periods of rain and a high number of mosquitoes carrying West Nile virus.

Weather outlook

The weather has significant impact on mosquito activity, Plaisance said. This winter is expected to be warmer and drier than normal, said Texas A&M University State Climatologist John Nielsen-Gammon. This could lead to an increase in the mosquito activity next year.

“Whether we have significant mosquito mortality will depend on how cold it gets,” Nielsen-Gammon said. “For the most part in history, every winter has gotten colder, [with the exception of] last winter. But we should occasionally have some substantially colder temperatures this year, so that should help with the mosquito population.”

Mosquitoes are cold-blooded and prefer temperatures over 80 degrees. At temperatures less than 50 degrees, mosquitoes hibernate for the winter, Plaisance said.

“If it does stay somewhat of a warmer winter then mosquitoes may still fly around, but they’re not going to be as active and I still expect the mosquitoes to hibernate,” she said.

Nielsen-Gammon said records have shown summer temperatures getting warmer across Texas, and for next year he expects warmer temperatures, but summer temperatures will depend on how much rain falls in the spring.

“This weather pattern this year was extremely crazy,” Plaisance said. “It’s too early to tell but I can only hope that we have a consistent season where we have a full fall and full spring. I hope we have seasons where we can have a gauge of what we can expect.”

The contract between Municipal Mosquito and the city for this year ends Nov. 15. However, Stallcup said depending on the weather forecast for the rest of year, the city may look into adjusting the final date.