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Bacillus thuringiensis subspecies israelensis, commonly referred to as Bti, is a bacterium found naturally in soils. Since 1982, it has been used successfully worldwide as a biological pest control agent to combat mosquitoes and black flies.
During the spore-forming stage of its life cycle, the Bti bacterium produces a protein crystal which is toxic only to mosquito and black fly larvae. These microscopic crystals are ingested by insect larvae when they are feeding. In the alkaline environment of the susceptible insect's digestive system, the crystals are dissolved and converted into toxic protein molecules that destroy the walls of the insect's stomach. The insect usually stops feeding within hours and dies within days.
Other subspecies of Bt are registered for use in Canada and these too work only on specific species of insects. For instance,Bt subspecies tenebrionis (Btt) is effective against Colorado potato beetles andBt subspecies kurstaki (Btk) works only against a group of insects called lepidopterans, which includes destructive tree pests such as gypsy moths, spruce budworms and forest tent caterpillars.
Bti is applied directly to the water where mosquito and black fly larvae are found. The bacteria are suspended in the water where the larvae will ingest it. None of the products containing Bti may be applied to treated, finished drinking water for human consumption.
Nearly all products containing Bti are Restricted class products used to control black fly and mosquito larvae in aquatic situations where the flow of water is not confined to a small area. Most provinces require that applicators be certified to use restricted class products. In some provinces, Bti use may also require a permit issued by the provincial pesticide regulatory authority.
Commercial class Bti products are also available, but can only be used to control black fly and mosquito larvae in private ponds and farm dugouts where no outflow beyond the property limits exists. Bti is also used to control fungus gnat larvae in greenhouse ornamental plants.
Bti poses little threat to human health through either handling products directly or being exposed to them indirectly, e.g. during a provincial or municipal mosquito control program. To activate Bti toxins, alkaline conditions that exist only in certain insects' digestive systems must be present. The acidic stomachs of humans and animals do not activate Bti toxins. There have been no documented cases involving toxicity or endocrine disruption potential to humans or other mammals over the many years of use in Canada and around the world. Studies have shown that even if Bti spores are ingested or inhaled, they are eliminated without any adverse health effects.
Prior to being permitted for sale or use in or import into Canada, all formulations are evaluated according to internationally-accepted scientific protocols for their potential to cause skin or eye irritation or sensitization and acute toxic effects. These tests are designed to show if the product has the ability to produce health effects or trigger allergic-type reactions.
The fact that Bti is a naturally-occurring, widely-distributed organism in the environment means that the average person would have multiple exposures to this bacterium throughout their lifetime, even if they never came in contact with a formulated product.
Applicator exposure during use in provincial and municipal mosquito and black fly programs is minimal, since the product is applied directly to the water where the larvae exist. None of the products containing Bti may be applied to treated, finished drinking water. Members of the public are unlikely to experience any symptoms if inadvertently exposed to Bti use, and no special precautions are necessary or required. Individuals who have concerns, however, should take reasonable precautions to avoid exposure during a spray program in the same way they would avoid pollen or other airborne materials during days when air quality advisories are issued. They can also reduce exposure by staying indoors with windows and doors shut during the spray period if spraying is taking place in their area, although this is not required by health officials.
Health Canada's Pest Management Regulatory Agency (PMRA) is responsible for ensuring the human health and environmental safety of all pest control products prior to their approval for use in Canada. Manufacturers must provide the Agency with a full analysis of the product formulation, as well as extensive health and environmental data, so that a risk assessment can be carried out by PMRA scientists. Only products that are scientifically reviewed and found to be effective and safe for use with minimal risk to human health and the environment are registered by the PMRA.
In Canada, the PMRA has classified nearly all Bti products used to control mosquito and black fly larvae as "Restricted", since they must be applied only in the water where the larvae exist.
Most provinces require that applicators who use restricted class products must be certified. As well, in some provinces, Bti use may also require a permit issued by the provincial pesticide regulatory authority.
In addition to the active ingredient Bti, other ingredients (formulants) are used to create the final product. It is mandatory for registrants of pest control products to inform the PMRA of all formulants used in a product. Formulant information is classified as a trade secret and the disclosure of this type of information to the general public is prohibited under the Access to Information and Privacy Act (ATIA). The individual formulants present in a pest control product are reviewed for any potential toxicological concerns or signs of being a potential irritant. If any human health risks are identified, steps are taken to either substitute the formulant, to address the identified health concern(s) by proper safety precautions and use restrictions on the product label or the product may not be granted registration approval.
Bti only becomes toxic in the stomachs of mosquito and black fly larvae. Because of this, it does not affect other insects, honeybees, fish, birds or mammals. The United States Environmental Protection Agency categorizes the risks posed byBt strains to non-target organisms as minimal to non-existent. The insecticidal toxin biodegrades quickly in the environment through exposure to sunlight and microorganisms.
Registered products containing Bti are primarily intended for use by trained applicators in federal, provincial and municipal mosquito and black fly programs. Label restrictions for these products permit the application only to the aquatic sites where mosquito and black fly larvae are found, and not to treated, finished drinking water. Following a review of human health risk assessments, Health Canada has determined that products containing Bti do not pose any health risks to humans and other mammals.
Based on the lack of human health risk and long history of safe use associated with Bti and other varieties ofBt, the PMRA has no human health and safety concerns with the application of registered products containingBt to bodies of water that will be used for human consumption. The direct application of Bti to treated, finished drinking water, however, is not considered acceptable practice by the PMRA.
Different varieties ofBt, including Bti, have been widely used in insect control programs in Canada and the US for many years and have demonstrated a remarkable safety record. The weight of scientific evidence indicates that Bti is non-infectious and non-toxic to humans and other mammals and poses little risk at dosage levels permitted in insect control programs. While adverse effects have been observed in individuals of some non-target aquatic insect species, no lasting impact on the populations of these species has been shown from use of Bti.
For more information about pest control products, contact Health Canada's Pest Management Information Service at 1-800-267-6315 or at (613) 736-3799 (outside of Canada).