DEPLW0704B 

Background

Mosquitoes and other biting insects are unarguably a nuisance in Maine. However, they also 

occupy an important part of the ecosystem, providing a hard-to-replace food item for other insects, 

amphibians, fish, and birds. Efforts to chemically control insects have the potential to cause far 

reaching environmental effects. Therefore, when considering using pesticides, you must proceed 

cautiously to avoid causing adverse impacts to aquatic life and habitats. 

Maine state law governs aquatic pesticide applications. If the area to be treated is a water of the 

State or if the treatment will potentially result in a discharge to a water of the State, you must first 

obtain a Maine Waste Discharge License (WDL). 

Applicable definitions and citations from rule and law

► Aquatic pesticide is defined as any substance applied in, on or over waters of the State or in such 

a way as to enter those waters for the purpose of inhibiting the growth or controlling the existence 

of any plant or animal in those waters (Department rule 06-096 CMR Chapter 514). 

► No person may directly or indirectly discharge or cause to be discharged any pollutant to a water 

of the State without first obtaining a license from the Department of Environmental Protection 

(DEP) (State law 38 MRSA, §413(1)). 

► “Waters of the State means any and all surface and subsurface waters that are contained within, 

flow through, or under or border upon this state or any portion of the State...except such waters as 

are confined and retained completely upon the property of one person and do not drain into or 

connect with any other waters of the state....” (38 MRSA, §361-A(7)). By definition, waters of the 

State include streams, rivers, lakes, ponds, marine waters, wetlands, and groundwater. In Maine, 

almost all wetlands are connected to either surface or ground waters, and some are connected to 

both. 

Chemical and biological agents

Various chemical and biological agents are marketed for control of mosquitoes. Chemical 

pesticides are not selective and have the potential to impact other species. Bacterial pesticides are

developed to impact species with specific properties, but may still impact more species than desired 

if improperly used. For example, the bacterial pesticides Bti (Bacillus thuringiensis, subspecies 

israelensis) and Bs (B. sphaericus) work on alkaline pH guts, which are found in mosquitoes, black 

flies, and some non-biting midges. Other bacterial agents may also affect butterflies and moths. 

Application of either type of pesticide to a water of the State requires a WDL. Pesticide 

applications to dry land with the potential to reach waters of the State during the time the pesticide

is active will also require a WDL pursuant to DEP Rules, Chapter 514. 

Waste discharge license (WDL) rule criteria

The Chapter 514 rules provide the following criteria for receiving a WDL to apply a pesticide to a 

water of the State: 

DEP FACT SHEET 

Aquatic Pesticide Applications for Mosquito Control 

Date: June 2008 Contact: Bob Stratton (207) 287-3901 or 

Toll Free 1-800-452-1942
June 16, 2008 DEPLW0704B 

A. The pesticide must be registered for the intended use by the U.S. Environmental Protection 

Agency (EPA) and the Maine Department of Agriculture, Food and Rural Resources’ Board of 

Pesticides Control (BPC). 

B. The applicant or agent must be licensed as a commercial applicator in the ‘Biting Fly and other 

Arthropod Vectors’ subcategory by the BPC. 

C. The applicant must provide adequate protection for non-target species. 

D. The applicant must demonstrate (1) a significant need to control the target species and (2) that 

the pesticide offers the only reasonable and effective means of control. 

E. The application must not result in violations of State water quality laws (such as impairing a 

waterbody so that it does not attain its designated classification). 

Items C, D, and E require SIGNIFICANT attention, as the DEP is concerned about the greater 

environmental effects of mosquito treatments. The DEP’s mission is to protect the quality, habitat, 

and designated uses of all waters of the State, therefore WDL applications for mosquito control will 

be stringently scrutinized. Some activities, however, can be conducted without DEP approval, as 

noted below. 

Activities that do not require DEP approval

The DEP has determined that treatments using granular or solid forms of Bti or Bs under specific 

conditions in high elevation (extreme tide) salt marsh pools, constructed ponds, and isolated 

freshwater wetlands do not require a WDL. In each of these resources, there must be a presence of 

mosquitoes and an absence of fish or other predators that can control them. In the salt marsh pools, 

the Bti or Bs must be placed immediately after pool flooding to enable its dissipation prior to the 

next flood event. The ponds and isolated wetlands must be contained on one person’s property and 

have no connection to other surface waterbodies. As an additional regulatory option, the DEP has 

developed a General Permit for Aquatic Pesticides for the Control of Mosquito-Borne Diseases. 

Coverage under the General Permit requires qualified projects to meet the criteria of Chapter 514 

above as well as specific conditions related to the title, but provides a more expedited process. 

Other information

To discuss requirements for mosquito treatment projects or obtain application materials, contact 

DEP’s Division of Water Quality Management at (207) 287-3901 or toll free 1-800-452-1942. 

Also, visit www.maine.gov/dep/blwq/docstand/wastepage.htm to view applicable rules or permit 

application materials (click on General Materials for rules; General Permits; or 

Municipal/Industrial, then Applications, then Aquatic Pesticides for forms). See also the DEP’s 

website www.maine.gov/dep/special_topics.htm and click on West Nile Virus for additional 

information and links to other sources, including the DEP Fact Sheet on Mosquito Control, West 

Nile Virus, and EEE. 

For more information on pesticides and their regulation and use, including requirements for 

Commercial Pesticide Applicator’s licenses and variance requirements near waters of the State, 

contact the Board of Pesticides Control at (207) 287-2731 or visit their website at: 

www.maine.gov/agriculture/pesticides.