Larva Control

After Education and Source Reduction, the “first line of defense” treatment for any environmental mosquito management program, is larva control (larviciding). Twelve hours of SCMAC’s 16-hour workday is spent larviciding.

Larva control involves the introduction of control products into aquatic habitats. The mosquito larva is the least mobile, most concentrated and accessible stage of the mosquito. By targeting larvae in ditches, flooded fields, flooded woodlots, neglected swimming pools, sewage lagoons, retention ponds, agricultural drains, and catch basins countless mosquitoes are eliminated before they reach the adult biting stage.

SCMAC's primary larva control product is Bacillus thuringiensis variety israelensis (Bti), a naturally-occurring soil bacterium. The bacterium produces proteins in a crystalline form. When mosquito larvae eat these crystals, the proteins cause a cellular breakdown in the alkaline midgut which results in rapid death. Bti has a highly specific mode of action and is widely considered to be of minimal environmental concern. Bti is specific to mosquito, blackfly, and midge larvae and non-toxic to mammals, birds, fish, and many insects including honeybees. Bti biodegrades quickly and leaves no residue. 

This larvicide will not kill mosquito pupae (3rd stage of the life cycle).

Aerial Larva Control

Learn more on our dedicated Aerial Control page


Seasonal vector control technicians begin larviciding immediately following the completion of spring aerial treatment. They concentrate on woodlots infeasible to treat by aircraft such as small woodlots less than 5 acres. Ground crews will use Bti or larviciding oil for this treatment depending on the mosquitoes’ stage of development.


Most roadside ditches are checked 1 to 3 times during the control season and treated when necessary. They are routinely checked after a significant rainfall as this often produces larval activity. Moving water is never treated.

Ditches are treated using truck-mounted “ditch guns” capable of “shooting” granular Bti or methoprene through vegetation to the water below. If late fourth instar larvae or pupae are present, larviciding oil is applied to the water with a hand-held wand. If the ditch cannot be accessed by a truck, treatment is made by ground crews using the above control materials.

Catch Basins

All villages, cities, and townships with urban development have catch basins. SCMAC recognizes these catch basins are a significant source of Culex mosquito (primary WNV vector) breeding and are larvicided whenever an area’s infestation is 25% or greater. The agency uses a variety of larvicide formulations and methods to treat nearly 100,000 catch basins annually. Methoprene larvicides (Altosid®) are applied by foot, bicycle, or truck targeting 30 day to season long control, depending on formulation, in catch basins located in subdivisions, parking lots, backyards, and busy roads. A mix of bacterial formulations,

VectoBac® WDG and VectoLex® WDG, are applied to roadside catch basins located in urban settings utilizing our fleet of mopeds. Catch basins are normally treated 2 to 4 times depending on mosquito infestation and disease activity. SCMAC continues to search for catch basins located off the road in residential backyards, school grounds, apartment and athletic complexes, and parks. 

Sewage Lagoons

Saginaw County has 13 sewage lagoon sites. The Field Department monitors infestation rates throughout the summer and the sites are checked and treated, if necessary, 2 to 4 times with bacterial larvicide most notably VectoLex® WDG.

Floodwater Habitat

Saginaw County has floodwater habitat that routinely floods and produces nuisance mosquitoes after substantial rain events. These sites may be treated multiple times; amount and duration of rain dictates amount of mosquito nuisance. These floodwater habitats include 

Field crews check and treat, as needed, known floodwater habitat after rain events. SCMAC has a substantial catalog of these known floodwater sites. Larvicide products used to treat these habitats include Bti, Natular®, and larviciding oil.

Thomas Township