mosquito larvaeA sound larviciding program is key in any successful integrated mosquito management program. A mosquito spends the first three stages of its life in the water as an egg, larva, and then pupa prior to hatching out into a full grown adult. Our larviciding program is designed to control mosquitoes in the water before they ever have a chance to emerge. It is crucial when running a mosquito control program to use tactics that are more economical so the taxpayers can get the most mosquito control for their money. Larviciding is one of the most economical ways to control mosquitoes because we are able to focus on a certain source with our pesticide applications rather than spraying miles of area for adults. There are many benefits to controlling mosquitoes in the aquatic stages of their life. Mosquitoes are both a nuisance and a vector of many diseases including west Nile virus. When we spray the mosquitoes as larvae we reduce the chance of there being a disease or a nuisance situation for that particular site because the larvae will never mature into adults.

Component of the Larviciding Program at WUVCD

WUVCD staffThe district is divided into 8 larvicide zones. We have a larviciding technician responsible for each zone. In our district, there are 1350 potential breeding sites that are checked weekly.

Each field technician is equipped with a truck, a power backpack sprayer, a hand powered liquid backpack sprayer, a map book, a handheld PDA for data entry, and pesticide. As our technicians inspect each breeding site, they enter in the source number, the larval size and number if present, the habitat, and the date/time into the PDA. If a treatment is needed, they then enter the size of the source, the material and amount used and the date/time. When the technician returns to our facility, the contents on the handheld are then downloaded into our database.

There are many different types of larvicides on the market for mosquito control. We use five different pesticides in our larviciding program. These five are broken up into two classifications, the biological, which are ingested, and surfactants, which use suffocation as a mode of action. We use Bacillus Thurengesis Isrealanis (Bti), which is a biological pesticide that is ingested by the mosquito larvae. BTI takes action within 24 hours and is specific to mosquito larvae making the environmental profile very good. We use BTI in both a liquid and granular form. Another biological product that we use is Bacillus Spharecus (Bs). Bs is also ingested by the mosquito larvae, however after the mosquito decomposes the Bs is re-released into the water, which gives us control for up to 30 days. Bs is sprayed out of a power backpack in a granular form and this product does not adversely affect other aquatic organisms. The surfactants used are Golden Bear 1111 and Agnique. Golden Bear is highly refined oil that is placed on the surface of the water to suffocate the larvae and pupae by taking away the surface tension and not allowing the mosquito to breath. We usually see result within 24 hours. Agnique is similar to Golden Bear by its mode of action, but Agnique is labeled to be used on potable water if necessary. We use it on ornamental ponds and other clean water situations. Agnique is effective within 48 hours after application.


As the mosquito season progresses, mosquitoes produced mostly agricultural areas move into our towns. As these numbers cross a certain threshold, the District begins its adulticide program. By reducing the numbers of mosquitoes, the odds of being bitten diminish. More importantly, when disease is present, the chances for transmission are lowered.

Adulticiding must be done during a temperature inversion. During the mosquito season, temperature inversions typically occur at dawn and dusk. So fogging is done early in the morning before most people are awake or active outdoors.

Mosquito activity peaks at both dawn and dusk. Fogging at one of these times allows for the best chance of impacting mosquitoes while decreasing the chances for an exposure in people. When the chances for public exposure are higher, as in town fogging, only the safest materials are considered for use.

The District always makes use of the local newspaper and radio stations to make residents aware of when spray operations will begin. Residents are encouraged to avoid sprays by staying indoors and by keeping doors and windows closed during July, August and September between the hours of 9:00 PM and 6:30 AM.

We would be happy to answer any questions or concerns you may have about this program. Please contact our office Monday thru Friday between the hours of 8 AM and 3 PM.