Larval Control
IRMCD’s larviciding program focuses on saltmarsh wetlands along the Indian River Lagoon. Approximately 2,000 acres of these wetlands are impounded and managed. The remaining saltmarsh wetlands and adjacent areas which produce mosquitoes require periodic larviciding (chemical applications to kill mosquito larvae).
The IRMCD employs nine field inspectors who routinely visit hundreds of known mosquito producing areas and check the water for the presence of larvae. If the affected area is small, these inspectors will usually apply an appropriate larvicide immediately to kill the mosquitoes. If the area is large or inaccessible, IRMCD aerially applies granular larvicides. The District does not aerially apply any liquid larvicides.
Larvicides
The IRMCD currently uses several different larvicides:
- Methoprene (Altosid) is a synthetic insect growth hormone. By applying it at the appropriate time in the mosquito life cycle, the larvae cannot make the transition from larvae to adult. Applied by the District as per the label, it is quite specific to mosquito larvae. Methoprene is approved for use in even the most protected environmentally-sensitive marshlands. IRMCD applies methoprene from the ground as a liquid and from the air as a sand granule.
- Bacillus thuringiensis israelensis, commonly known as “Bti” (Vectobac) is a naturally occurring bacterium which affects insects that have an alkaline digestive chemistry such as mosquitoes. It must be ingested in order to be effective. Applied by the District as per the label, it is quite specific to mosquito larvae. Bti is approved for use in even the most protected environmentally-sensitive marshlands. IRMCD applies Bti from the ground as a liquid and from the air as a corn cob granule.
- Temephos (Abate) is an organophosphate insecticide to which mosquito larvae show extraordinary sensitivity at very low dosages. Abate is labeled for use in environmentally sensitive habitats. IRMCD applies temephos from the ground as a liquid and from the air as a granule.
- Other products occasionally used which kill mosquito larvae and pupae at the water’s surface are: monomolecular film (Agnique), and a larviciding surface oil (Golden Bear).
None of these larvicides are persistent in the environment. They kill the mosquito larvae present at the time of application and then rapidly decompose. If a heavy rain occurs a few days after treating with these larvicides there is no alternative but to treat once again.
The manufacturers of several larvicides also offer time-release solid formulations which IRMCD uses in small areas. Expense and the possibility of the insects developing resistance to these larvicides preclude the use of time-release formulations on a larger scale.