County will reverse course with mosquito spraying plan

Giving targeted, on-the-ground spraying a shot

Gunnison County will not conduct aerial spraying for mosquitoes this summer, opting for a more targeted, on-the-ground approach to season-wide mosquito control. This is a departure from past efforts, which used the aerial application of a Permethrin-based insecticide to squelch the mosquito population before the Fourth of July. The shift comes in response to concerns over the environmental effects of aerial spraying, and is in many ways the result of a simple question: Was there an alternative to aerial spraying?

“Spraying has been presented really starkly by both perspectives as all or nothing,” said county manager Matthew Birnie. But he started to wonder if there was a middle ground that could account for public health concerns, like exposure to West Nile virus and overall comfort, and one that would be less environmentally disruptive. After the county’s most recent meeting with the Colorado Parks and Wildlife Commission, there was even more reason to look into the matter.
“We’ve obviously got the Gunnison sage grouse listing decision on the horizon, and there was some assertion at the Parks Commission meeting early last week that spraying might have an impact. There’s not necessarily evidence of that, but it’s just one more factor,” Birnie said.
Trap counts (a way of monitoring mosquitoes) also show that aerial spraying provides effective short-term control, but doesn’t offer protection all summer long. Mosquitoes rebound after spraying. So Birnie contacted Colorado Mosquito Control (CMC), which conducts mosquito control for Gunnison County, to see if there were alternatives to aerial spraying. He wanted to know the options if the county shifted its budget for aerial spraying—sometimes as high as $95,000—to treating mosquito larvae, an alternative that is non-toxic and point-specific.
It turns out that CMC can conduct on-the-ground spraying throughout the summer, specifically focusing on highly populated areas and even spraying for mosquitoes prior to events like outdoor concerts or sports camps. That keeps spraying where it’s needed most, and leaves ecologically sensitive areas spray-free.
“What it came down to was efficacy and ecology, and what was the best balance of that,” said Birnie, and the commissioners evidently agreed. Birnie says the decision did not require board action but he consulted with each of the commissioners prior to making the switch.
It’s a decided shift in perspective by the board, which heard from many members of the public after last summer’s aerial spraying led to a large die-off in the stonefly Classenia sabulosa on area rivers. The stonefly is considered an indicator species and provides an overall measurement of ecosystem health.
But in spite of the packed courthouse, the commissioners favored keeping aerial spraying in place for the sake of public health. Instead they opted to support local studies to better understand the effects of spraying on aquatic ecosystems.
According to Birnie, this latest decision changes the baseline. Instead of studying the effects of spraying on the aquatic insect population, the county can compare the effects of targeted ground spraying to the efficacy of aerial spraying on the mosquito population. Birnie is optimistic. The county will have access to trap counts and other data, and will no doubt hear from the public.
During any given summer the county already receives requests for on-the-ground spraying. With more resources available, Birnie thinks the county could be better able to respond. “We might be more responsive to target events, problem areas, and places where people are congregating,” he said.