A pesticide is defined as any substance or mixture used to prevent, kill or repel a pest. In the case of WNV, the pest is the mosquito or mosquito larvae, and the pesticide is either an adulticide or a larvicide.

The Huron County Health Unit does not plan to use pesticides in the year 2006. If there are positive mosquito pools found in high-risk areas or confirmed human cases then larviciding may be considered in our county.

Larviciding

Source: Benton County Mosquito Control District.

Larvicides are chemical or biological products registered for use by the Pest Management Regulatory Agency (PMRA) of Health Canada. Larvicides are governed by strict regulation under the Pesticides Act in Ontario; the Ministry of the Environment regulates this act. Non-residential larvicides can only be applied by trained and licensed applicators. The applicators must obtain a permit, issued by the Ministry of the Environment, for each site that is to be treated.

Larvicides used in WNV control are used in pellet form and are dropped into catch basins to control the growth of mosquito larvae before they reach adult form. It is important to note that larvicides would not be sprayed or applied through the air.

Types of Larvicides:

The two types of larvicides that are most commonly used are methoprene and Bti.

Methoprene:

• Methoprene is a growth regulator that interrupts the mosquito life cycle and prevents immature mosquitoes from developing into biting adults
• Methoprene is highly effective, has low environmental impact and poses no risk to the health of mammals
• Research has shown that methoprene, when used to reduce mosquito larvae according to its directions, does not pose a risk to human health.
• Direct contact may cause mild eye and skin irritation.
• Methoprene breaks down quickly in water and soil in the presence of sunlight, and it will not remain in the ground or leach into ground water
• It is applied in pellet form to treat roadside catch basins

See Health Canada's fact sheet on the use of methoprene in mosquito control programs for more information.

Bti (Bacillus thuringiensis israelensis):

• Bti is a bacterium, which contains protein crystals that rupture digestive cells in mosquito larvae when ingested
• Bti is applied in granular form
• Bti has no acute or chronic effects on humans, other mammals, or aquatic organisms
• It represents a very low risk to other non-target species and would only be used on temporary standing water such as ditches

See Health Canada's fact sheet on Bti for more information.

Larviciding on Private Property

There are strict guidelines regarding pesticide use on private land. You do not need a permit to larvicide stagnant water, as long the water does not drain off of your property. However, a permit is required to treat catch basins on private property.

For more information regarding permit applications visit the Ministry of Environment website.

If you choose to larvicide stagnant water on your property there is a product called AquaBac (containing the active ingredient Bti) that is federally approved and can be purchased at local hardware stores. Please note that the manufacturer's instructions must be strictly followed at all times.

Adulticiding

An adulticide is a chemical pesticide used to kill adult insects. The most commonly used adulticide is malathion. Malathion is spread through the air from an ultra low volume (ULV) sprayer on the back of a pick-up truck.

For more information about adulticiding and malathion, visit the Ministry of Environment's website.

Alternatives to Pesticides

Health Units in Ontario have researched and continue to research natural predators and other alternatives to pesticides.

Bats:

• Bats are natural mosquito predators, however, research indicates that they prefer to feed on larger insects such as moths and beetles
• There is also a concern with increasing the bat population because they are known to carry rabies

Purple Martins:

• Purple martins are not effective for mosquito control
• Martins are active only during the day and feed high in the sky, while mosquitoes are active at night and fly low to the ground

Dragonflies:

• Dragonflies do eat mosquitoes but are only active during the day
• Dragonflies normally inhabit larger ponds and creeks that do not support large populations of mosquitoes
• Results indicate that dragonflies are not effective in controlling the spread of mosquito borne disease even though they have been used in the past for mosquito nuisance control

Mechanical Devices (e.g., zappers, traps, etc.):

• Mosquito traps/magnets emit C02 or other chemicals that attract mosquitoes. A fan then sucks them into the trap. They are typically used for mosquito surveillance and are not effective in reducing the number of mosquitoes in a person's backyard
• Bug zappers claim to control mosquitoes, but they kill many other beneficial insects as well

Although natural predators such as bats, birds, and dragonflies eat adult mosquitoes, their presence alone would not be a sufficient control method for WNV.

For more information regarding mosquito control and pesticides, visit Health Canada's Pest Management Regulatory Agency website.