Ramping up for ‘Mosquito Season’ by Patrick Linn, MS, MSHAPI Executive Director, CMCD

Helicopters and drones disperse granular larvicide as a pre-treatment during late winter / early spring.

Yes, there are subtle, seasonal shifts in Southwest Florida’s weather, and if you’ve been here long enough you can detect them. But one season persists year-round: mosquito season. During the winter months, variations of dry/wet, cool/warm  conditions  can either increase or decrease mosquito populations. Only when dry conditions persist, and temperatures consistently drop below 55 degrees, will mosquitoes slow down or find a place to hide until it warms up again. So, don’t put away that repellent!

Typically, when cooler, drier conditions occur during late winter/early spring, Collier Mosquito Control District prepares for the warmer, rainy weather – and the increase in mosquito populations – by ramping up “pre-treatment” applications of
materials to target mosquito larvae in area waters. The District uses two granular larvicides: Natular G30 (Spinosad) and Vectoprime FG (Bacillus thuringiensis, subsp. Israelensis or Bti). These granular, organic larvicides look similar to kitty litter and are dispersed at low altitudes over waterways via District helicopters and drones.

Both Spinosad and Bti – used in organic farming – are naturally derived from soil bacteria. When dissolved in water, they can control mosquito larvae up to 30 days. The spores in these materials target and only affect the larvae of mosquitoes, blackflies,
and fungus gnats in the water. Neither poses any toxicity to humans, pets, fish, or plants.

The District’s granular larvicide materials resemble kitty litter, and pose no toxicity to people, pets, fish, or plants.

During 2019, the District applied more than 40,000 pounds of granular larvicide materials, representing a 25 percent increase over the previous year. Interrupting the mosquito life cycle by preventing emergence has proven very effective in reducing
mosquito populations.

These naturally derived materials represent a key element in the District’s integrated mosquito management program. In addition to dispersing Spinosad and Bti larvicides, residents are encouraged to acquire free mosquitofish (Gambusia holbrooki) from the District for placement in standing water where mosquitoes breed. Native to Southwest Florida, each 2-inch-long fish can eat up to 100 mosquito larvae daily. Non-working fountains, swales, and flooded yards are a few of the most common places residents are using these fish.


Want to learn more about the District’s operations? We welcome visitors for tours of our campus, and residents are always encouraged to call ahead to pick up mosquitofish. Tours include presentations by our scientific team in the laboratory, our operations/surveillance team, and a visit to the hangar. Please call our office at (239) 436-1000 to schedule a tour or if we can provide more information.

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