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Spring high tides bring island mosquitoes

By Staff | Jun 4, 2018

With recent high tides and rains, mosquito season is here and it could be a doozie. Our population is overwhelmingly salt water mosquitoes. Having lived on Sanibel for close to 40 years, I have witnessed many changes in mosquito control methods – all for the better.

My first mosquito control experience was a DC3 plane spewing smoke in the sky over my live aboard sailboat at Jensen’s on Captiva. I thought the plane was crashing when in reality it was spewing diesel mixed with Malathion to kill flying adult mosquitoes. Thank goodness that does not happen on the islands anymore! The low volume spraying from helicopter or truck used today does not need a mixer like diesel – much better for the environment. Malathion is no longer used because the insects have such a fast life cycle they built up resistance to the pesticide.

From my office window overlooking the grass swale behind the SCCF Nature Center, I recently saw a mosquito control helicopter spraying the standing water at about 10 a.m. A call to the Lee County Mosquito Control District confirmed that the helicopter was treating for mosquito larvae, not flying adults. The product being spread was granular BTI, Bacillus thuringensis israelensis, which kills only mosquito larvae – very environmentally friendly. Low volume spraying is used throughout our mangrove coastal areas these days. Both fish and dragonfly larvae eat mosquito larvae.

Salt water mosquitoes (Aedes spp.) lay their eggs in the soil, not standing water. If the spring high tides that hatch their dormant eggs would stay high, there would be no place for them to lay their eggs. If the rains would completely fill up the interior fresh (brackish) water wetlands, there would be no place for the salt water mosquitoes to lay their eggs. It is the wet and then dry cycle that keeps them going.

Well, the yearly cycle has begun and there are adult mosquitoes flying. The first spraying for adult mosquitoes happened on-island the night of May 31. Have you seen the LCMCD truck that drives around with a huge mesh funnel on top? The adult mosquitoes are wind scooped in and later counted, triggering when the trucks drive through the neighborhoods spraying for the flying adults – only from dusk to dawn. The pesticide used to kill the adults is permethrin. The trucks are low volume sprayers.

Permethrin is a synthetic pyrethrin and is not so good for any insect that flies at night. It is definitely harmful to bees, which thankfully don’t fly at night but do fly pretty early in the morning. Our island bee keepers should pay attention.

As a long-time islander, I view mosquito season as my winter – a time to stay inside dusk to dawn. Walks on SCCF trails are on hold for now. Pray for big rains that will keep the wetlands full so the otters will swim up from the Sanibel River and feed on crayfish in the grass swales. The most beautiful mosquito free summers at the SCCF Nature Center happen when rain water stands in the wetlands winter, spring, summer and fall.

Dee Century is the Living With Wildlife Educator at the Sanibel-Captiva Conservation Foundation.