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Larviciding Efforts
Mosquito & Aquatic Weed Control >​​ Mosquito Control > Larviciding Efforts
The most environmentally sound and effective method of mosquito control is an Integrated Pest Management program (IPM program). This program reduces breeding sites, uses biological controls, and, when needed, uses chemical control to maintain mosquito populations at a tolerable level. The IPM program takes into consideration an insect’s ability to become resistant to chemical treatments over a short period of time. With the mosquito’s quick reproduction time and numerous offspring, resistance could become a major problem.

Source reduction, the elimination of potential and existing breeding sites, is by far the preferred method of control. Any time we can reduce the breeding areas without the use of another control method, we would prefer to do so. Examples of source reduction include special ditches in salt marsh areas that harbor natural mosquito predators, good drainage of run-offs ditches and catch basins, and elimination of water holding artificial containers around homes through public education (see also Mosquito Control At Home).

The second choice would be the use of biological control. Biological control is the improvement and utilization of nature’s own mosquito control. Many animals feed on mosquitoes during their larval, pupal, and adult stages. As larvae and pupae, mosquitoes may be eaten by water beetles, dragonfly nymphs, water scorpions, damselfly naiads, giant water bugs, beetle larvae, crayfish, freshwater shrimp, tadpoles, other mosquito larvae, and a large variety of fish. As adults, mosquitoes are eaten in large quantities by dragonflies, frogs, toads, damselflies, lizards, nighthawks, swallows, martins, and various other birds. This interdependence with other organisms in the environment is very important. The total elimination of the mosquito may, therefore, adversely affect the entire food chain cycle.

Biological control can also be achieved by the use of a larvicide material. Upon studies of the mosquito, we know during the larval stage mosquitoes eat algae, plankton, bacteria, and any small detritus in the water. Based on this knowledge, our program utilizes a biological larvicide that targets mosquitoes specifically. This larvicide is made of a bacteria found naturally in the soil called Bacillus thuringensis var. israelensis (Bti). It is mixed with water and sprayed onto the water where the larvae are found. The benefit of this product is that it does not affect other organisms. Bti is ingested by the larvae and a bacterial spore is formed in the midgut. Death occurs shortly thereafter. Because Bti must be ingested, it only works during the larval, or feeding, stage. Resistance to this product is nearly nonexistent. Bti can be sprayed using our larviciding trucks or by using our helicopter.

If the use of Bti is not feasible because of mosquito age (in the pupal, non-feeding stage) or regular access to a breeding site is not possible, other larviciding methods are employed. Larviciding pellets or briquets containing mosquito growth hormones can be used to alter the development of the mosquitoes by limiting growth in any aquatic stage. The pellets or briquets slowly release the growth hormones into the water column to provide lasting control. The hormones were developed by studying the lifecycle of the mosquito closely and are selective for mosquitoes. Pellets and briquets are dispersed by hand. Resistance is possible, therefore, it is not utilized in all situations. We also use an oil for larval and pupal control. This oil makes a thin coat on the surface of the water and prevents larvae and pupae from getting the air that they breathe. This oil is used in last case scenarios because it is not mosquito specific. It degrades quickly in the environment and resistance is nearly nonexistent.

Adulticide treatments usually occur after all attempts to control the mosquitoes have been exhausted. It can be performed using either ground or air equipment. Adulticide is not as selective and resistance is common.​

 
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