Frequently Asked Questions about West Nile Virus

Mosquito Control

Q1. What is mosquito control?
Q2. What is the life cycle of a mosquito?
Q3. What types of standing water have mosquitoes?
Q4. How can landowners control mosquitoes in standing water?
Q5. How are pesticides (larvicides) used to control mosquitoes?
Q6. How are pesticides (adulticides) used to control mosquitoes?
Q7. Will pesticides be used to control mosquitoes in New Brunswick?

Q1. What is mosquito control?

Mosquito control is using various measures to reduce the numbers of mosquitoes. Control of mosquito populations is based on an integrated pest management strategy focusing on non-pesticide control of mosquito populations to the extent possible. As the risk level increases, additional mosquito abatement measures will be considered to reduce mosquito populations, including pesticides to reduce mosquitoes and their larvae.

Q2. What is the life cycle of a mosquito?

There are 74 known mosquito species in Canada and not all the species are found in all parts of the country. Mosquito life cycles are very complex and different for each species. They all have different habitats, behaviour, preferred sources of food (blood), and type of standing or still water needed to complete life cycles.

There are four stages in a mosquito's life cycle: egg, larva, pupa and adult. Some mosquito species lay their eggs on moist surfaces, such as mud or fallen leaves that may be near water but are dry. Later, rain or high tides reflood these surfaces and stimulate eggs to hatch into larvae. Other mosquito species deposit eggs directly onto the surface of standing or still water and these eggs will hatch into larvae.

The larval and pupal stages must be in water. Larvae live in the water and come to the surface to breathe. They feed on organic material in the water, grow and eventually become pupae. Pupae also come to the water surface to breathe and this stage develops into adult mosquitoes. When the mosquito is fully developed the pupae splits and the adult mosquito emerges. The adult rests on the water's surface while all of its parts harden and its wings dry. Then it is ready to fly.

Q3. What types of standing water have mosquitoes?

The type of standing water is different for each species, and depends on factors like the amount of water, the depth of the water, the amount of vegetation, and the pollution level. Not all sources of standing water are necessarily good breeding areas for mosquitoes. Large lakes, ponds, and streams that have waves and lack aquatic vegetation around the edges do not contain mosquitoes.

Of the 74 known mosquito species in Canada, West Nile virus has been found in ten species. Even though mosquitoes may be present in areas, they may not be the species that can carry West Nile virus. Some of the mosquito species that can carry West Nile virus are called "container breeders". These mosquito species breed in very small amounts of standing water that is stagnant and more than four days old.

Q4. How can landowners control mosquitoes in standing water?

Public education and awareness are the basis for reducing the risk of West Nile virus. Once West Nile virus is detected in an area, preventing mosquito bites is the most effective measure to reduce personal risk and must always be considered, even if other measures are taken. Another measure to reduce the risk is to eliminate breeding sites by removing stagnant water from your property.

Landowners can eliminate mosquito breeding sites from their yards and private property by reducing the availability of standing water that is suitable for mosquito larval and pupal growth. These breeding sites can include clogged rain gutters, wading pools and other children's toys, tires, birdbaths and ornamental pools. Water can be prevented from accumulating in these objects by removing them, cleaning them, and changing the water in objects, or aerating water that is found in ornamental pools.

Do not attempt homemade remedies to control mosquitoes in standing water, like placing oils in the water. Not only is this damaging to the environment, it is illegal. If you feel you need to control mosquitoes in standing water, contact a professional pest control operator. They are listed in the yellow pages under "Pest Control Services".

Q5. How are pesticides (larvicides) used to control mosquitoes?

Mosquitoes develop through four life stages: eggs, larvae, pupae, and adults. Eggs are deposited by female mosquitoes on or near a wide variety of standing or still waters. Larvae hatch from eggs and feed and develop in these habitats, usually over a period of several weeks.

Larvicides are chemical or biological agents that are used to destroy mosquito larvae. They are usually applied to standing water where larvae are developing. Larvicides can be used to control mosquitoes whenever larvae are present. They may be used during the spring and summer months to reduce local mosquito populations in areas where West Nile virus activity is anticipated.

Q6. How are pesticides (adulticides) used to control mosquitoes?

Adult mosquitoes usually rest on plants and other vegetation when not feeding.

Adulticides are chemical agents that destroy adult mosquitoes. These products are usually applied to vegetation or are sprayed as fine droplets in the air to contact flying mosquitoes. Adulticides may need to be re-applied to maintain control of the mosquito population.

All other preventive measures (reducing risk, preventing mosquito bites and eliminating mosquito breeding sites) should be used even if pesticides are used to control mosquitoes.

Q7. Will pesticides be used to control mosquitoes in New Brunswick?

The decision whether to use pesticides (biological or chemical agents) to control mosquitoes in New Brunswick is very complex and depends on many factors. The size of the affected area, the proximity to populated areas, the timing of the mosquito breeding season, and the risk of human exposure to infected mosquitoes are all factors a community and public health authorities must consider when determining the most appropriate mosquito control option.