WEST NILE VIRUS AND LARVICIDING
What is larviciding?
Mosquitoes have a 3 stage lifecycle in the water: egg, larva and pupa. Larviciding involves the use of
approved chemical or biological pesticides to control mosquitoes at the larval stage, before they can mature
into adult mosquitoes and disperse.
Why is Durham Region larviciding?
Durham Region’s West Nile virus (WNV) Vector Control Plan includes the use of pesticides to help reduce and
control WNV mosquito populations. The use of larvicides is considered when other measures to reduce and
control mosquito breeding sites are inadequate.
Research shows that roadside catch basins are prime breeding sites for mosquitoes associated with WNV. As
a result, monitoring and larviciding of regional and municipal catch basins have become necessary
components of the Vector Control Plan. Surveillance and/or treatment of standing surface water on regional
and municipal property will be based on a WNV risk assessment.
What about private backyard catch basins?
Catch basins in residential backyards may be larvicided under Durham Region’s Vector Control program on a
request basis; subject to a local risk assessment.
When will larviciding take place?
Larviciding programs are best conducted through the late spring and summer months. Durham Region
contracts a licensed pest control company to conduct its larviciding program. Generally, three catch basin
treatments are planned; with the first occurring in mid-June, the second in mid-July and the third in mid August
each year. The timing of larvicide treatments is based on larval mosquito surveillance results.
Who regulates the use of larvicides?
The management of pesticides is a federal and provincial responsibility. Health Canada’s Pest Management
Regulatory Agency (PMRA) is responsible for assessing pesticides to determine their safety, merit and value.
The Ontario Ministry of the Environment (MOE) regulates the sale, use, transportation, storage and disposal of
federally registered pesticides in Ontario under the Pesticides Act and Ontario Regulation 63/09. The
application of certain larvicides requires a permit from the MOE, and can only be applied by trained and
licensed personnel.
What larviciding products will be used?
The Ontario Ministry of the Environment has currently approved only three (3) larvicides for use in Ontario,
over . . .
methoprene, Bacillus thuringiensis israeliensis (Bti) and Bacillus sphaericus (Bsph).
For more information
DURHAM REGION HEALTH DEPARTMENT
905-666-6241 1-800-841-2729 or durham.ca
If you require this information in an accessible format, contact 1-800-841-2729.
WNV AND LARVICIDING
What is it
and how
does it
work?
How will it
be used?
Are there
any risks
associated
with the
product?
Methoprene
Bti
Bsph
Methoprene is a synthetic insect
growth regulator that was first
registered for use in 1977. This
chemical pest control agent prevents
mosquito larvae from maturing into
adults.
Bacillus thuringiensis israeliensis,
commonly known as Bti, is a
bacterium found naturally in soils.
Once in the digestive system of the
mosquito, it secretes an enzyme that
destroys the insect’s stomach walls.
The insect usually stops feeding
within hours, and dies within days.
Bacillus sphaericus is a bacterium
found naturally in soil and aquatic
environments. Once in the digestive
system of the mosquito, it secretes an
enzyme that destroys the insect’s
stomach walls. The insect usually
stops feeding within hours, and dies
within days.
Altosid pellets will be used in
targeted catch basins, when
mosquito larvae are identified. It is
applied in pellet form, and gradually
sinks to the bottom of the water. Over
the next 21 days, it is slowly released
to the surface in small amounts, and
eventually eaten by the larvae.
Methoprene breaks down rapidly in
the environment.
Methoprene is not sprayed into the
air.
Vectobac or Aquabac granules will
be applied directly to the surface of
stagnant water (ponds, ditches)
when mosquito larvae are identified.
Bti is suspended in the surface of the
water, and is ingested by the larvae.
In some instances, Bti may have to be
reapplied on a weekly basis since it
biodegrades quickly in the
environment with exposure to sunlight
and microorganisms.
Bti is not sprayed into the air.
Vectolex® granules or water soluble
pouches may be used for larval
mosquito control in catch basins. A
single application of Bsph is effective
in controlling mosquito larvae for an
extended period of time.
Bsph is not sprayed into the air
Studies indicate that methoprene is of
low toxicity and poses little risk to
people when used according to
manufacturer’s instructions. Since
methoprene will be applied directly to
the catch basin, human or animal
exposure is minimal. It is known to be
slightly toxic to some aquatic life.
Bti only becomes toxic in the alkaline
stomachs of mosquito and blackfly
larvae. Following a review of human
health risk assessments, Health
Canada has determined that Bti does
not pose any health risks to humans
and other mammals. Studies have
shown that even if Bti spores are
ingested or inhaled, they are
eliminated without any adverse health
effects.
Health Canada has determined that
Bsph is not harmful to human health
when used according to
manufacturer’s instructions. Bsph has
minimal effect on non-target species
of aquatic life.
Will I be kept informed?
Prior to the application of the larvicide, the Durham Region Health Department will provide advance notification
of the treatment sites in accordance with MOE requirements (i.e. newspaper notice and/or posting along the
perimeter of the treatment area). Up to date information will also be posted on our website at: durham.ca.
Are there any products available for household use?
Bti and Methoprene products are available for household use and can be purchased at some garden supply
and hardware stores. These products can only be used to control mosquito larvae in self-contained bodies of
water (private ponds, farm dugouts and ornamental ponds), where no outflow beyond the property exists. Bti
and Methoprene are not approved for public use in catch basins. Remember to always follow
manufacturer's instructions on the proper use of the product.
More information can be obtained from
Durham Region Health Department, Environmental Help Line
905-723-3818 or 1-888-777-9613
April 22, 2013
For more information
DURHAM REGION HEALTH DEPARTMENT
905-666-6241 1-800-841-2729 or durham.ca
If you require this information in an accessible format, contact 1-800-841-2729.