Btk for Control of Gypsy Moth

What is Btk (Bacillus thuringiensis subspecies kurstaki)?

  • Bacillus thuringiensis subspecies kurstaki or Btk is a naturally occurring bacterium in soil.
  • In Canada, Btk has been used as a biological pesticide for over 30 years to control pests, such as the gypsy moth, that infest our forests and agricultural lands.
  • It is also used on organically-grown produce.

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Are gypsy moths a problem in Halton?

  • Gypsy moth infestations can cause moderate to severe defoliation of certain types of trees.
  • Healthy trees can usually withstand losing their leaves for a few years. However, several years of defoliation can severely weaken or kill trees.
  • The gypsy moth population has reached a critical level in a number of areas in Halton.

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How does Btk work?

  • The Btk bacterium produces protein crystals that are poisonous only to the larvae (caterpillar) of certain moths and butterfly species.
  • Btk does not affect adult moths and butterflies and must be eaten by the larvae in order to be effective.

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How is Btk used?

  • Btk bacteria protein crystals and spores are mixed with water and other ingredients called formulants to produce a pesticide product (Foray 48B). The formulants help the pesticide to stick to the leaves and needles of trees.
  • Btk must be applied to the leaves of the host trees. The spray can be applied directly with a hand held sprayer to individual or small groups of trees or from a helicopter or small plane to urban forest areas and larger rural forested landscapes. Btk must be applied by a licensed operator.
  • A number of municipalities in Ontario have used Btk to control gypsy moth larvae. Aerial spraying has recently been used in both Mississauga and Toronto to manage gypsy moth outbreaks.

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Are there any health concerns related to the use of Btk?

  • Over many years of use worldwide, no public health problems have been identified from the use of Btk. Health Canada and the World Health Organization (WHO) have concluded that Btk poses little threat to human health through direct handling of the product or indirect contact that can result from a spray program.
  • Health Canada indicates that Btk does not appear to affect the immune or endocrine systems. No toxic effects have been demonstrated in humans or other mammals. Studies of the formulants in the Btk pesticide did not find any significant health risks.
  • Minor skin, eye or respiratory irritation has been reported in some unprotected spray workers. However, in such cases the exposure to Btk was to amounts up to 500 times greater than what the average person would be exposed to during a spray program.
  • Health Canada states that no special precautions are necessary or required when spraying Btk. However, individuals who still have concerns about Btk can reduce exposure by staying indoors with windows and doors closed when Btk is being sprayed in their neighbourhoods.

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What should I do if I feel I am having a reaction to Btk?

  • Members of the public are unlikely to experience any symptoms as a result of a Btk spray program.
  • If you do have symptoms after a Btk application and are concerned, see your doctor.

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Photo of Gypsy moths laying eggs.
Gypsy moths laying eggs
Photo courtesy Royal Botanical Gardens

What is the effect of Btk on the environment?

  • Btk breaks down quickly on leaves through exposure to sunlight and micro-organisms. For example, Btk sprayed on leaves will normally break down within one to four days. Btk is not toxic to mammals, birds, fish or most insects such as honeybees. Activation of Btk toxins requires alkaline conditions that exist only in the digestive systems of certain insects. The acidic stomachs of animals and humans do not activate the release of Btk toxins.
  • Furthermore, for the activated Btk toxins to work, they have to become attached to the surface of a cell lining the digestive system. Only the guts of certain insect species have the correct attachment sites for the Btk toxin. Btk does not survive in warm-blooded animals and humans and passes through their digestive systems without producing toxic effects.

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Who regulates Btk use in Canada?

  • Btk is the active ingredient in Foray 48B, a pesticide product registered in compliance with Health Canada’s Pest Control Products Act and regulated by the Pest Management Regulatory Agency (PMRA).

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Where can I find more information about Btk and gypsy moth control?

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This fact sheet has been prepared using sources from Health Canada, the World Health Organization, Region of Peel, City of Mississauga and Toronto Public Health. March 2008