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Insect Control

Frequently Asked Questions

Mosquito Control

Tell me about the City's mosquito control program.

This season’s mosquito control program will continue to be based on an environmentally mindful insect control strategy including larviciding, residual treatments, and when necessary, fogging, to supplement these ongoing measures. 180 staff working in the Insect Control will deliver the key components of the mosquito control program including:

  • A larviciding program that continues to be 100% biological and uses four larviciding helicopters,
  • Monitoring and treating over 31,500 hectares of water area on an ongoing basis based on weather conditions,
  • Monitoring for adult nuisance mosquitoes in New Jersey Light Traps begins early May with trap counts posted on the Insect Control website

Fogging programs that will only be initiated when the requirements of the City policy, the AFA Guidelines, and the Provincial Pesticide Use Permit are met. If nuisance mosquito fogging is required, the program will be carried out using DeltaGard® 20EW®. Areas with highest nuisance mosquito populations will be prioritized first and 90 meter buffer zones will be respected. A 24-hour public notice will be issued prior to the start of a nuisance fogging program. Daily public notice will also be issued detailing where fogging will occur that night.

When will fogging for nuisance mosquitoes occur?

Fogging will occur if the weather produces conditions under which the larviciding program is unable to control mosquito populations. The City of Winnipeg Adult Mosquito Control Policy and the Pesticide Use Permit define three requirements that must be met for a nuisance mosquito fogging program to occur:

  • The Adulticiding Factor Analysis (AFA), which is one city-wide rating, must be High, AND
  • a minimum average city-wide trap counts threshold of 25 female mosquitoes for two consecutive nights must be met, AND
  • one or more of the quadrants of the city must be in the range of 100 female adult mosquitoes.

Fogging will be carried out by prioritizing areas with high nuisance adult mosquito populations and then progressing to other parts of the City if required. 24 hour advance notice will be given before any fogging program begins. If nuisance mosquito fogging is required, the program will be carried out using DeltaGard® 20EW®.

Why do you need to close public spaces when you are larviciding with helicopters now?

Transport Canada Civil Aviation Division has updated the standards on the low flight waiver which allows the City to use contracted helicopters to apply larvicides at low altitudes. As a result, when larviciding is occurring in places where people congregate (e.g. athletic fields, larger parks, golf courses etc.) public access will be restricted to these areas 20 minutes before and during treatment. Treatment time generally ranges from 15 - 60 minutes. This new standard is solely due to the possibility that a helicopter could have mechanical troubles and is out of an abundance of caution.

The Insect Control will try to minimize disruption to the public in the areas impacted by the new standards by posting signage which indicates the date and time of the planned treatment approximately 24 hours in advance of treatment, treating as early as possible in the morning and using longer lasting larvicides to limit the number of applications required over the season.

How do I register for a buffer zone?

Property owners not wanting insecticides applied on or adjacent to their principal residence may register as “Anti-Pesticide Registrants” for the adult nuisance mosquito control program. Those who wish to register must provide identification that ties the registrant to the address being registered for a buffer zone. A photocopy or scanned document such as a driver’s licence or a utility bill will suffice as acceptable identification proving primary residence. Remember – a 72-hour turnaround time is required.

There are four different options to register:

  • 311 Self Service Request
  • In writing to the Insect Control at 3 Grey Street, Winnipeg, MB R2L 1V2,
  • By emailing 311 at, and
  • By faxing 311

Please note that since identification is required, registrations cannot be processed over the phone.

What is the City doing to reduce the need to fog?

The City has implemented a phased-in environmentally friendly, aggressive larviciding program in an effort to reduce the need for residential fogging. Larviciding is the most effective and environmentally-friendly approach to controlling mosquitoes, as it targets mosquito larvae in the aquatic stage before they emerge as adults.

In 2016, the City also launched an awareness campaign – Agents of SWAT – to encourage homeowners to fight mosquitoes before they hatch by draining, dumping or covering standing water in their yards because 50% of Winnipeg’s mosquito population comes from standing water on private property.

Is the City prepared to deal with an outbreak of West Nile Virus this season?

The City of Winnipeg works collaboratively with Manitoba Health for surveillance, monitoring and control measures for West Nile Virus (WNV). As in previous years, the City of Winnipeg plans for WNV and has the necessary resources to carry out all WNV activities from surveillance to control measures including larviciding and adulticiding. Each year, the City works with the Province on a targeted larviciding program which focuses on Culex tarsalis and restuans. A WNV adulticiding program would only occur under a Provincial health order. Specific questions on populations of Culex tarsalis and restuans and WNV program details should be directed to Manitoba Health.

What is the AFA?

The Adulticiding Factor Analysis (AFA) is a range of factors that the Superintendent of Insect Control considers when deciding what control measures should be implemented, i.e. larviciding, barrier treatments, fogging. The AFA is rated as Low, Medium, or High based on the following factors:

  • soil moisture conditions
  • forecasted rainfall
  • percentage of nuisance adult mosquitoes collected from New Jersey Light Traps
  • the current stage of adult mosquito generation
  • the current degree day model in conjunction with the current environmental conditions and outlook
  • the current status of larval development sites and the outlook for adult mosquito emergence in the short term.

Forest Tent Caterpillar

What are forest tent caterpillars?

Forest tent caterpillars, a species native to North America, is the most prolific of forest defoliators. These defoliators, although an infrequent pest in Winnipeg, can cause considerable damage when an outbreak erupts. Outbreaks occur about every 15 years and last about 3 years. While aspen is its preferred host, during severe infestations the forest tent caterpillar will feed on maple, oak, birch, ash, fruit trees, elm, deciduous shrubs and some garden plants.

What do forest tent caterpillars look like?

The adults are tan coloured, with two thin, dark, parallel oblique lines or one single, broad, dark band crossing the middle of the front wings. The mature larvae are 45-55 mm long and are bluish to brownish in colour with diamond-shaped white spots on the middle of the back of each segment. It has 2 thin, prominent broken yellow lines that extend along each side of its hairy body.

What is the life cycle of the forest tent caterpillar?

Adult moths emerge in early July and lay their eggs in a single gray-brown band 1.5-2 cm deep that encircles a small twig of the host tree or shrub. Within three weeks, a young larvae forms within the egg, but it remains dormant until the following spring. When the leaves begin to open, the larvae emerge and begin to feed in early May. During the early larval stage, they can be often found clustering in masses on the stem or trunk. The larvae feed over a 4-6 week period before becoming pupae. They form their cocoons between 2 leaves of a tree, on shrubbery or on buildings where they can find a sheltered location.

What does forest tent caterpillar damage look like?

Larvae feed initially on the opening buds, later consuming parts of or whole leaves of broad-leaved deciduous trees and shrubs. During high populations, forest tent caterpillars can completely strip trees and will then feed on the understory shrubs and other vegetation.

Will my tree die?

Healthy trees grow back their leaves three weeks after defoliation. However, after repeated defoliation, trees may be more susceptible to secondary insects and diseases.

What is the City doing to control forest tent caterpillars?

The forest tent caterpillar control program will focus on areas where trees are at risk of significant leaf damage based on surveillance data conducted during the winter. Treatment will be conducted utilizing Foray® 48B (Bacillus thuringiensis var. kurstaki - Btk), a biological product.

How can I control forest tent caterpillars?

On smaller trees and shrubs, an effective means of controlling forest tent caterpillars is pruning or breaking off the egg masses on the twigs and disposing of them in the garbage. This is best done in fall or in early spring when there are no leaves on the trees and the egg masses are most visible. After hatching, young colonies of larvae can be pruned off or squashed while they are resting in clusters on the main stem, especially in the evening or on cool nights.

When trees are too large or there are numerous larvae, a non-chemical insecticide, Bacillus thuringiensis var. kurstaki (Btk), can be sprayed when the caterpillars are about 1-2 cm long. Tanglefoot banding your trees will not be effective in controlling the forest tent caterpillar as the female moth is winged and can fly to the twigs and branches to lay her eggs.

Elm Bark Beetle

What is the purpose of the Elm Bark Beetle control program?

The program is intended to control elm bark beetles, the carriers of Dutch Elm Disease (DED).

What treatment does the City use to control elm bark beetles?

Treatment will be conducted using Pyrate® 480EC (chlorpyrifos), a chemical product, which is sprayed from portable sprayers directly onto the lower 50 centimetres of the tree trunk. This product has been approved for use in Canada by Health Canada’s Pest Management Regulatory Agency, and will be used in accordance with federally approved label directions by licensed pesticide applicators.

What does the elm bark beetle look like?

The adult beetle is small and cylindrical. The length of the beetle measures 2 to 3.5 millimetres. It is brownish black in colour and has short hairs over its body.

How do I recognize if my tree is infected?

Look into the tree canopy, wilting of leaves is usually the first stage of DED, followed by yellowing then browning of the leaves. If you are unsure please call 311 for a forestry technician to inspect.

What should I do if the tree looks unhealthy?

If your elm tree looks unhealthy and you are not sure if it has DED, please call 311 - they will send a service request to the Urban Forestry Branch for a technician to inspect the tree. More information about DED is available at Urban Forestry.

Last update: October 7, 2020
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or 1-877-311-4WPG
Media inquiries: 204-986-6000

Administrative Office and Research Laboratory
1539 Waverley Street
Winnipeg MB R3T 4V7

Operations Base
3 Grey Street
Winnipeg MB R2L 1V2
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