As long as larvacide is specified for use in aquatic environments and applied according to directions, no Water Quality Permit is required for its use; however, should a water quality violation/fish kill occur, the entity doing the application is responsible. Ellen Gilinsky, Virginia Water Protection Permit Program Manager, Virginia Department of Environmental Quality P.O. Box 10009, Richmond, Virginia 23240, Phone: 804-698-4375 Fax: 804-698 4347 or Harrisonburg Regional Office of the DEQ at 540-574-7800.
 

Relevant section in the West Nile Virus Task Force Manual: 

A. Chemical Control

1. General - If it becomes necessary to resort to the use of chemical pesticides for the control of mosquito vectors of WNV, state and local governments will provide residents with accurate and precise advance information on when and where these pesticides will be applied so that they may take action to protect themselves, pets, and domestic animals (including managed honeybee colonies). A list of pesticide active ingredients registered in Virginia for mosquito control is provided in Attachment 4.C. The use of insecticides for mosquito control is accompanied by risks to non-target organisms including humans. Direct toxicity is the primary concern, and it may be reflected in fish or wildlife kills or in episodes of non-lethal effects which render exposed organisms susceptible to other sources of morbidity or mortality. When choosing mosquito control pesticides, governmental agencies and their contractors should give preference to those pesticides which pose the least risk to humans and the environment. Relative risks (toxicity) of the currently registered mosquito control pesticides, both larvicides and adulticides are discussed in Attachment 4.C. Whenever any pesticide is applied, the law requires that the directions outlined on the pesticide label be carefully followed. Any fish kills must be reported immediately upon discovery. During business hours contact the closest regional Department of Environmental Quality office; otherwise contact the Department of Emergency Management at 1-800-468-8892.
  

2. Larval Mosquito Control - In general, larval control is the most effective in preventing disease transmission and has the least effect on non-target species and the environment. Localities may conduct their own larviciding activities or contract with commercial pesticide applicators to control mosquitoes in the aquatic state before they become biting adults. Applications of larvicides encompass fewer acres than adulticides because treatments are made to relatively small areas where larvae are concentrated as opposed to larger regions where adults have migrated. The larvicides that can be used for mosquito control in Virginia include the following:
  

a. Microbial larvicides such as Bacillus thuringiensis var. israelensis and Bacillus sphaericus can be used successfully in a broad range of freshwater habitats, but are somewhat unpredictable in salt marsh habitats.

b. Biochemical larvicides (insect growth regulators - IGRs) such as methoprene can be used in a variety of habitats, and are especially effective in salt marshes. However, sustained release methoprene products should not be used in known fish habitats.

c. Mono-molecular surface film larvicides can be highly effective in polluted or artificial habitats, but should not be used where non-target insects are important resources. While this eliminates most natural areas, they may be used in some sewers where Culex pipiens, the principal vector of WNV, may deposit their eggs.

d. Abate (temephos), an organophosphate insecticide can be effectively used in certain situations such as in the treatment of standing water, shallow pools, swamps, marshes, in polluted waters high in organic content, and in catch basins.

3. Adult Mosquito Control - Application of mosquito adulticides should be considered the least desirable method of control and only used when current isolations of virus or evidence of disease has been established (Levels III and IV). Pesticides currently registered in Virginia for adult mosquito control include organophosphates, pyrethrins, and pyrethroid-based insecticides. These mosquito adulticides may be applied by properly maintained and calibrated backpacks or truck foggers, or fixed-wing or rotary-wing aircraft. Mosquito adulticides currently registered in Virginia are listed in Attachment C. Each of these pesticides has its own strengths and drawbacks that will influence which material is most appropriate for a given situation (Attachment 4.C). Localities seeking additional guidance on appropriate mosquito control pesticides should contact the Virginia Cooperative Extension at Virginia Polytechnic Institute and State University , Blacksburg , Virginia .

4. Aerial Application of Mosquito Control Pesticides - Since aerial application of mosquito control pesticides can apply insecticide to wide areas much more quickly than other methods, both fixed-wing and rotary-wing aircraft are appropriate options for dispersing insecticides should there be an imminent threat of arthropod-vectored disease (Levels III and IV). Properly certified applicators must be aboard each aircraft conducting aerial pesticide applications. Both larvicides and adulticides may be applied by aircraft. State and local public health and other governmental agencies may establish pre-existing requirement contracts with commercial pesticide applicators that can be activated on a moments notice, should wide-area mosquito control become necessary. When the potential for arthropod-vectored disease transmission is so high that it exceeds the capability of local resources to respond in a timely manner, the state may request assistance from the Department of Defense for aerial application of mosquito control pesticides by the U.S. Airforce.

5. Timing of Pesticide Applications - The application of mosquito control adulticides must be properly timed in order to be most effective. Depending upon the target species, generallyspeaking the greatest efficacy will be achieved when adulticides are applied around dawn or dusk. Since Culex pipiens, a night biter, appeared to be the primary vector of WNV to humans in New York, adult control activities should be conducted around dusk and into the nighttime hours unless mosquito surveillance or epidemiologic evidence indicate otherwise.