Franklin County details mosquito-control strategy after heavy rains; officials stress larval treatment and targeted adult sprays

Jason Gates, Franklin County’s mosquito and tick-borne disease control specialist, told the Board of County Commissioners on July 9 that heavy recent rains have pushed mosquito populations “back to square one” and that the county’s first line of control is treating larvae.

Gates said, “Our main objective out there when we're trying to control mosquitoes, it's always at the larval state. We use a product called BTI.” He explained that BTI is a naturally occurring bacterium applied to standing water where larvae develop and recommended commercially available “dunks” for small private sources such as bird baths.

The program uses larval control when technicians find breeding sites they can treat directly. Gates said the county buys BTI in bulk for larger sites and that adult truck-based spraying is used only in two circumstances: when mosquito testing yields positive West Nile virus results that push the county’s calculated “vector index” above the department’s threshold, or when nuisance-trap counts exceed a numeric threshold (he said a trap count must exceed 50 to trigger a nuisance spray evaluation).

Gates described the adult spray product used by the county as containing permethrin and piperonyl butoxide, and said it is applied at very low concentrations — “a shot glass, less than a shot glass, roughly over a football field” — and that “the spray only lasts 15 minutes.” He said the product’s active ingredients are synthetic derivatives of naturally occurring compounds and that the program uses integrated pest management to limit unnecessary spraying.

Gates addressed common public concerns and misinformation: bats and bat houses can help but will not eliminate mosquitoes; citronella and lemongrass-based repellents reduce bites by an estimated 40 percent in some studies while oil of lemon eucalyptus may reduce bites by roughly 60 percent; and DEET or other registered repellents produce higher immediate protection. He also said that male mosquitoes can act as pollinators and that spraying after sunset reduces expected contact with bees.

On operational constraints, Gates said weather and wind strongly affect spray drift and effectiveness and that crews attempt to limit spray where people are present by stopping the sprayer when they encounter residents. He described the county’s practice of not spraying within 500 feet of properties on a Department of Agriculture “hypersensitive” list and said aerial spraying is an infrequent option used by the state only when vector surveillance and public-health inputs justify it.

Commissioners thanked Gates for the presentation and for the public-education emphasis. Commissioner Flannery said the talk helped explain common concerns raised by residents on social media, and the chairman complimented Gates’s presentation.

The mosquito program update was provided as an informational briefing; the board did not take formal action during the presentation.