Mosquito tracker: West Nile-positive insects down in Pennsylvania
Although West Nile Virus has afflicted nearly a dozen people in Butler County this year, the region’s mosquito coordinator said the number of subjects testing positive for the disease are down throughout the state compared with last year.
The Pennsylvania Department of Conservation and Natural Resources since 2022 has released information about mosquitoes on its website using the “Skeeter Meter,” which also helps track the risk of West Nile Virus county by county.
The risk level for West Nile Virus has remained in the very high range for the past few weeks, but Claire Covert, mosquito program coordinator for the Department of Conservation and Natural Resources, said it is still lower than the same time in 2025.
But the risk is still there.
“Around this time last year, there were around 3,000 West Nile positives, and this year we only have 1,000,” Covert said Sept. 10. “I would say the … hotter months like July and August (have more), but since the hot weather is stretching into September, there’s a lot now.”
West Nile virus risk in Pennsylvania was very high the week of Sept. 14, meaning that virus activity has been found “very frequently” in mosquitoes collected in Pennsylvania, according to the DCNR. The Mercer County Conservation District oversees the mosquito-borne disease control program for Butler County, as well as Mercer and Crawford counties.
On the Skeeter Meter’s webpage, the DCNR urges individuals to control mosquitoes around their homes by reducing standing water where mosquitoes gather, live and breed. Personal protection measures, such as using repellents and wearing pants and long sleeve shirts, are encouraged to avoid mosquito bites, according to the DCNR.
Covert said people should clear standing water from indoor spaces and even from their yards as much as they can. She said the ability of mosquitoes to breed and the amount of eggs per batch can cause populations to boom quickly, if left unchecked.
“Mosquitoes can breed in spaces as small as a bottle cap,” she said. “No matter how small, they lay their eggs in standing water. I think for some species it can be like 300 (eggs).”
Covert is one of many mosquito program coordinators throughout Pennsylvania. She also does tick surveillance for the Mercer County Conservation District.
To track insect populations and test them for disease, Covert and the conservation districts across the state use special traps to gather samples. And the conservation district has different traps for different situations.
There are three main traps used in the Mercer County Conservation District.
The gravid water trap is typically set up are mostly set at or near wastewater treatment plants for detection of West Nile Virus carrying mosquitoes. The gravid water trap uses water high in organic matter to attract mosquitoes looking for breeding locations, and operates by sucking mosquitoes through a hole in the bottom of the box into a collection chamber.
The CDC mini light trap uses light to attract mosquitoes and is commonly equipped with a carbon dioxide lure. The trap operates by sucking mosquitoes through a hole in the top of the white net sock into a collection chamber at the bottom of the trap. These are set in a variety of locations to trap both blood meal seeking and non-meal seeking mosquito.
The BG Sentinel 2 Trap uses contrasting colors, carbon dioxide and scent to attract mosquitoes looking to feed off small mammals. The trap operates by sucking mosquitoes through a hole in the top of the white upper section into a collection chamber. These are mostly set at Equine Encephalitis-monitoring locations or in areas of mosquito complaints to determine the population size and composition.
Covert said she sends trapped mosquitoes for tests once a week.
“All of those traps contain a fan that sucks the mosquito up into a net. Once we get them, we freeze them and count them and ship them to scan for diseases,” Covert said. “Usually, we ship them the day we count, and the next week we get the results.”
Mosquitoes are the deadliest animal in the world, according to Covert, and not just when it comes to humans. They can also transfer diseases to animals, which kill livestock and wild animals throughout the world. Covert said mosquitoes can transfer Eastern Equine and Jamestown Canyon Virus to animals like horses, alpacas, llamas and the like, which is “very deadly to them.”
And that’s not to diminish the deadly risk that ticks present. Covert said tick populations are down overall this year, even though one species, Asian Longhorned ticks, are up 103% this year compared with last year.
Ticks populate Pennsylvania around the same time as mosquitoes, but the nymphs and eggs are usually laid in leaf litter, and adult ticks like to hang out near the forest edge and tall grass, Covert said. She also said that, in general, tick diseases are “not as much of a problem” as those from mosquitoes.
“It’s definitely a problem; however, we don't do control for tick diseases,” she said.
Mosquito season is April to October, so once October is over, the population monitoring is done, according to Covert. However, if warm weather sticks around later, Covert said population monitoring may need to expand.
“The colder weather stretches out the development times,” Covert said. “It reduces standing water, and many adults die off in the winter, but some enter a resting state, called diapause, and they bury themselves in soil. Some eggs are able to hatch.”
The Skeeter Meter can be found online on the DCNR’s website. Individuals can submit mosquito complaints on the website, too, which are answered by the DCNR.
