Some of these changes are the result of efforts to control saltmarsh mosquitoes in the late 1950’s through the early 1970’s. The saltmarsh mosquito doesn’t lay its eggs in standing water; this is a defense mechanism against predators. These mosquitoes lay their eggs in mud or moist sand, waiting for rains to come and raise the lagoon levels to flood the sand or mud, allowing the larvae to mature before predators such as the mosquito fish can eat them.
Previous efforts to control mosquitoes involved the use of chemicals such as DDT, but the mosquitoes quickly evolved resistance to DDT so other measures had to be used. One method that quickly gained favor in Florida was called “source reduction.”
In source reduction the ability of the salt marsh to produce mosquitoes is decreased by reducing the habitat that the mosquitoes need to breed in. In the slide below we see a fairly large pond with an area of bare sand to the upper left. Although this is actually a spoil pile it illustrates the bare areas much like this that are the sort of breeding habitat that mosquitoes use. When the water level rises as the summer rains begin, water floods the bare sand, the eggs hatch and the larvae are able to mature and hatch out. The idea behind source reduction is to take away that habitat that mosquitoes need to breed in.