The Pasco County Mosquito Control District has an Aquatic Weed Control Program. We do not control weeds for beautification purposes. We only attempt to control plants that harbor certain mosquito species, or to thin out areas such as floating plant mats where growth is so thick that natural predators (e.g. minnows) can't find the mosquito larvae and pupae.
Our primary efforts include the control of two exotic floating plant species: Water Hyacinth (Eichornia crassipes) and Water Lettuce (Pistia stratiodes). These plants support the development of the pest mosquitoes Mansonia dyari and Mansonia tittilans. A third pest mosquito, Coquilletidia perturbans , is also associated with aquatic weeds. It is found on a number of types of rooted plants along the edges of lakes, ponds, canals, and ditches.
The larvae and pupae of these three species attach to the root hairs of plants with a modified air tube. They extract oxygen from the surrounding water and likely from the plant itself. They feed on microscopic plant and animal life that floats by. They do not go to the water's surface to breathe like other mosquito species. Consequently, they are difficult to detect by both their natural predators and by mosquito control technicians.
To find the plant communities that support these mosquitoes, several techniques are employed. When Mansonia adult mosquitoes are collected in one of the suction traps which are placed throughout the District, we have an idea of the general location of the larval rearing site. Our field personnel will then search for Water Lettuce and Water Hyacinth. If necessary, the suspect area may be searched using a helicopter. Once the Water Hyacinth and/or Water Lettuce is found, herbicides are applied which will kill the plants, effectively reducing mosquito population numbers.
Mansonia mosquitoes were present in Florida and utilized the root hairs of desirable native vegetation prior to the introduction of the exotic plants they thrive on. It is unlikely (and undesirable) that we will ever be able to rid ourselves of them. Controlling the exotic plants helps check a mosquito population that is out of balance with nature. Because we do not target all floating plants, those that exist on desirable native vegetation can continue with their natural functions in our ecosystem.
In contrast, native rooted aquatic plants are found
along most ditches, canals, and shores of our streams, rivers, lakes and
ponds, making it very difficult to determine specific Coquilletidia production
sites. Strong public opinion supported by law and environmental agency
rules prevents the widespread removal or destruction of shoreline vegetation
which would at least temporarily eliminate the mosquito locally.