Mosquito Control

Frequently Asked Questions

Why does Portsmouth have a mosquito control program?

Portsmouth has a dual-purpose mosquito control program, addressing both "nuisance" mosquitoes and mosquitoes of public health importance. 34% of Portsmouth is wetlands, where mosquitoes breed and develop. Additionally, since Portsmouth is a seacoast community with flat topography, numerous additional temporary, stagnant, shallow water areas develop due to snow melt and rain, adding to mosquito breeding areas. Without mosquito control to reduce the number, there would be many areas that would be inundated with biting mosquitoes. Although different species may also be found to be carrying dangerous diseases, the same mosquito control components useful for nuisance mosquitoes can quickly be directed at controlling disease carrying mosquitoes. Portsmouth also has an older population which is generally more susceptible to mosquito borne diseases.

Who does mosquito control?

Mosquito control is done by licensed professionals contracted by the City. They have the expertise and knowledge of mosquito biology, appropriate types of controls, Integrated Pest Management (IPM) techniques, and the environment. The current contractor is Municipal Pest Management Services, Inc., 19 Oak Terrace, Kittery, ME 03904. Tel: (603) 431-0008.

Who permits mosquito control?

Mosquito control requires an annual permit from the State of New Hampshire, Department of Agriculture, Markets and Food, Division of Pesticide Control. Every commercial and private pesticide applicator must be licensed in the safe and legal use of pesticides. Re-certification is also required every 5 years to ensure licensed applicators remain current in their knowledge of pesticides.

What methods are used?

Integrated Pest Management (IPM) is used to develop a comprehensive, safe, and effective mosquito-control program. IPM promotes a sustainable approach to managing pests by maximizing the use of biological, cultural, and physical controls, thereby limiting chemical methods to minimize health and environmental risks, and economic loss when controlling pests.

Mosquitoes are easier to control before they are able to fly. Mosquito "larvae" are the immature stage of a mosquito's life cycle and are found in stagnant water. There can be 100,000 mosquito larvae in a square meter of water and it takes only 4 days to develop into flying, biting mosquitoes. These environments are where they are most vulnerable to control efforts. Controlling mosquito larvae is called "larviciding". Once a mosquito develops wings and moves into the larger environment, it becomes harder to control. Controlling winged mosquitoes is called "adulticiding". Street spraying is a form of "adulticiding".

What pesticides are used and are they safe? 

The primary control for larvae in stagnant waters is a naturally occurring bacterium called Bacillus thuringiensis, or Bti. Bti affects mosquito larvae, black fly larvae and midges. The bacterium is specific to these organisms.

The insecticide used in street spraying for adult mosquitoes is called Anvil. Anvil is a synthetic copy of a natural insecticide found in Chrysanthemum plants. Anvil is designed for use in residential areas and is applied in minute amounts. Anvil breaks down very quickly in the environment and does not accumulate.

How do you decide when to spray?

Truck spraying along city streets is decided upon by reviewing the data collected from mosquito trapping and by citizen complaints. Mosquito trapping tells us what species are present and in what numbers. If citizen complaints are unusually high or if the data shows elevated populations of mosquitoes associated with human disease, then street spraying is done.

What if I don't want my property sprayed?

The City honors request for "no spray" from residents. If you do not want your property truck sprayed or larvicided, contact Public Works at 603-427-1530 or notify Municipal Pest Management Services, Inc. directly at 603-431-0008 or email at

What if I grow organic vegetables?

People with organic gardens should contact Public Works and/or Municipal Pest Management Services. They will evaluate the area and implement a plan to prevent the street spraying from contacting their crops.

What if I keep bees?

Street spraying applications are done at night when most bees are not active. Anvil has been used in the City for the past eight years with no recorded bee kills. It is recommended that anyone with bees contact Public Works or Municipal Pest Management Services, Inc. and report the exact locations of hives to prevent hives from being directly sprayed.

What can I do to reduce mosquitoes on my property/in my home? 

Make your property less habitable to resting mosquitoes. Check outdoor containers that could allow water to collect such as bird baths, planters, wheel barrels, children's toys, etc. Shallow, stagnant waters such as deep puddles and seasonal wet areas that are suspected mosquito breeding areas should be checked by professionals. No person should ever apply anything to water without approval from the state. This includes the mosquito dunks found in retail stores. Keep lawns mowed and clear the understory of wooded areas adjacent to your property. These are areas where mosquitoes rest during the day to prevent from being exposed to direct sunlight.

To learn more about what you can do to protect yourself and reduce mosquito breeding on your property, please click here.

Do all mosquitoes carry disease?

No. There are many mosquito species that do not bite humans at all. However, in periods of high mosquito populations and high levels of disease in local bird populations, the likelihood for human contraction is greater.

What if I find a dead bird? Should I contact someone about it?

The state lab is no longer testing birds for WNV and EEE, the Portsmouth Health Department is still interested in reports of dead birds to keep abreast of any unusual clusters. Please report any dead birds to Kim McNamara, Health Officer at (603) 610-7273. Please indicate, if known, the type of bird, where found, when found, condition (i.e. appear hit by a car, possibly caught by a cat or a dog, no signs of trauma, wings spread out, etc.)