Fewer Mosquitoes, A Healthier Lagoon

It was evening, friends were over and mosquitoes were coming out. I lit a green mosquito coil and Eden inhaled deeply as smoke wafted up. “Ah,” she said, “the smell of my childhood!” Mosquito coil smoke is a smell that every child who grew up in coastal Florida in the 1960’s, when the salt marsh mosquito ruled, knew well. I asked Eden if she would jump on her bike when the mosquito truck came by, pedal like crazy to catch up, enter the cloud of insecticide in the truck’s wake and yell “The mosquito man, the mosquito man!” “Of course,” she answered.

The salt marsh mosquitoes, Aedes taeniorrhynchus and Aedes sollicitans shaped our Florida lives and landscape back then. It isn’t a major disease carrier, but its mouthparts are adapted for piercing and sucking, and it does this with a fierceness that makes all other mosquitoes seem meek.

The State of Florida first tried to kill off the salt marsh mosquito with DDT, but by the 1950’s, mosquitoes started to develop resistance to the pesticide. People were also concerned about toxic effects, and DDT was banned in the United States in 1972. Then researchers found that by flooding salt marshes where mosquitoes laid their eggs, they could control the mosquitoes without heavy use of pesticides.

Most mosquitoes lay their eggs in water. Salt marsh mosquitoes, however, lay their eggs in the muddy soil above the water line. These eggs lay dormant until water rises with tides or rain and floods the eggs. Females lay eggs, rain or shine, and these add up during dry spells. Concentrations of 20,000 eggs per square inch have been found in mud above the water in salt marshes. When eggs are inundated, they all start developing at once. Five to seven days later an explosion of hungry, adult mosquitoes emerge. Males survive on nectar. Females can lay one clutch of eggs without eating but require a blood meal to lay additional clutches of eggs. Their main source of blood is birds and mammals, but they will eagerly take blood from people.

Salt marshes flooded to control mosquitoes are called mosquito impoundments. Brevard County, originally named Mosquito County, created the first impoundment on Merritt Island in 1954. Today there are 28,000 acres of impounded marshes in Brevard County. Ditches were dredged around the perimeter of salt marshes, and the earth was piled up to form berms which separated salt marsh from the adjacent estuary. Water, either pumped in from outside the berm or flowing from artesian wells inside the impoundments, was kept at unnaturally high levels. By keeping the soil that salt marsh mosquitoes lay their eggs on permanently submerged, breeding grounds were eliminated and mosquito numbers went down.

DDT caused great environmental harm. It soon became apparent that mosquito impoundments caused great harm too. When salt marshes became isolated from the rest of the estuary, important salt marsh benefits were eliminated from the bigger ecosystem. Young fish could no longer escape to salt marshes to avoid becoming a meal for bigger fish. Impoundments stopped the flow of detritus and nutrients from the marsh to the adjacent water body. Water quality inside the impoundments deteriorated. Salt marsh vegetation often died from high water or extreme salinity. The health of the Indian River and other estuaries suffered.

We’ve learned a lot since the early days of mosquito control. We are better at controlling salt marsh mosquitoes while limiting damage to the Indian River. Salt marshes have been reconnected to the lagoon with culverts installed through impoundment berms. Now water and fish travel back and forth between salt marsh and estuary from October to May, when the mosquitoes are not actively breeding. Culverts are closed during summer months so water levels can be manipulated to destroy breeding habitat. Care is taken now not to over-flood impoundments. Water, kept at the level of the average high tide, is high enough to prevent mosquito breeding but low enough to avoid killing salt marsh vegetation.

According to Keith Minner of Brevard County’s Mosquito Control District, Altosid is the main pesticide used now. It is applied to water to kill mosquito larvae, and it only kills mosquito larvae. Aerial spraying of the pesticides Naled and Kontrol 44 kill adult mosquitoes. Spraying is done less frequently, and the pesticides used today are safer than those used in the past.

I also spoke with Shannon Maginnis from Mosquito Control. When I asked if kids still followed mosquito trucks, he laughed and said “I hope not.” When he was only eight or nine and the other neighborhood kids were pedaling through the insecticide haze, he knew it wasn’t a smart thing to do. Now drivers are instructed to turn the spray off if kids try to follow, and they don’t try often. Kids in coastal Florida no longer idolize the Mosquito Man because they don’t know what it’s like to live with salt marsh mosquitoes.

We are controlling mosquitoes and the environmental consequences of controlling mosquitoes, but the Indian River still suffers from other environmental assaults. Thick muck deposits, built up over decades, cover much of the Lagoon’s bottom. Muck is easily stirred up, blocking sunlight needed for photosynthesis and killing seagrass. Nutrients that feed deadly algae blooms enter the Indian River from leaking septic tanks, stormwater runoff and people’s lawns. This algae dies and decomposes, uses up oxygen in the water, and fish die too. Plastic trash washes into the lagoon and breaks into tiny pieces. Oysters eat it, their eggs become shriveled, their sperm are slow and their young aren’t as good as they should be. Some of these problems are difficult to solve. Getting plastic out of the Indian River is easy. Grab a bag from a BlueTube, pick up trash and throw it away. No BlueTube at your favorite riverfront park yet? Sponsor one and make it easy for everyone to keep the Indian River cleaner.