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The products used

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In 2001, Quebec made an important decision of import to society by banning the use of chemical pesticides in forest environments. Since that time, several new organic products have been developed that can be divided up into four main groups: insect disease bacteria, pheromones, viruses, and insect pathogenic fungi. However, in relation to the epidemic management strategy adopted by the Quebec Ministry of Natural Resources, only one group of products has proven its efficacy – namely, insect disease bacteria such as Bacillus thuringiensis. Thus, for the time being, the only insecticide formulations authorized for the purpose of controlling forest insect pests in Quebec are those based on Bacillus thuringiensis subsp. kurstaki (Btk). This organic pesticide is applied over infested forests by means of specialized aircraft, at a dosage of 1.5 litres per hectare – i.e., approximately the area of a football field.

Btk - origins and uses

The organic pesticide known as Btk has been used in forest areas in Quebec since the mid-1980s, and has been used throughout the world in other sectors for more than 50 years now. In all these years, no serious infection and no public health problem have been reported. Btk is a safe product regularly used in different formulations in agriculture, gardening and public health; some formulations have even been approved for use in organic farming. As Btk has been approved for use in agriculture, both Health Canada and the US Environmental Protection Agency have prescribed no upper limit with respect to food. Through our diet, a number of us have already been exposed to Btk without knowing it – and above all without experiencing any consequence! Several other varieties of Bacillus thuringiensis have been registered (i.e., certified) as insecticides for treating other orders of insects. One example that comes readily to mind is Bacillus thuringiensis subsp. israelensis (Bti), frequently used in the field of public health to control biting insects. Its use is even authorized for application in drinking water supply intakes.

In Canada and the United States, Btk formulations have been used within the framework of several protection programs targeted at indigenous pests as well as in programs aimed at countering the expansion of undesirable exotic insects. Out of all these programs, more than a hundred covered inhabited urban areas. One example that comes readily to mind is that of Victoria, British Columbia, where, in 1992, the entire downtown area was the object of protection. In all instances, measures were implemented for monitoring public health, and no major incident could be linked to these programs. On the contrary, monitoring efforts showed that Btk formulations were safe for human health.

Fact sheet on Bacillus thuringiensis subspecies kurstaki (PMRA, february 2000) :
Public Health Advice on the utilization of the organic insecticide Bacillus thuringiensis in forest, agricultural and urban habitats (MSSS, 1995)

Btk – The bacteria and its presence in the environment

Btk is a bacterium that lives naturally in soils, where it was initially isolated. However, it can also be found in water or on vegetation even when no spraying has occurred. In keeping with the scientific literature on the subject, SOPFIM reached this conclusion on its own after performing annual environmental follow-up as part of its forest pest management programs. It is not uncommon to find low concentrations of Btk in watercourses, water intakes and in the soil prior to the start of operations. And, though the presence of Btk can be detected in water, the bacterium does not proliferate in that medium. Despite repeated spraying in the same sector over several years’ time, no increase in the quantity of Btk in the environment has been noted in 20 years of follow-up.

Mode of action

Bacillus thuringiensis is a bacterium having the ability to produce a protein crystal that is converted into a toxin whenever it is placed in an alkaline environment. As it so happens, insects belonging to the order of Lepidoptera, which includes the main forest insect pests in Quebec, all have a basic (alkaline) digestive system. Whenever a lepidopteran feeds on foliage treated with Btk, the toxin released by the protein crystals destroys the walls of its gut, thus forcing the insect to stop feeding. Death usually occurs two to five days later. Btk must be ingested by the insect in order to produce a toxic effect; it is not a contact insecticide.

Specificity of product

Bacillus thuringiensis is a bacterium that is highly specific to insects, as the protein crystals are only able to release their toxin in an alkaline environment. The reason Btk is more specific to lepidopterans than to other insects having an alkaline stomach is that its toxins are able to bond with specific enzyme receptors located inside the gut. If no such receptors are present, the toxins are unable to produce their effects on an insect. As a result, this insecticide does not affect other orders of aquatic or soil insects. Concerning the 282 other species of lepidopterans that are not targeted for treatment in Quebec, the impact has been assessed as being less than negligible. As was stated in an impact study conducted in 1992, only 10 species of lepidopterans could potentially be present in forest areas at the time of spray operations (i.e., June). However, the presence of these 10 species depends on the occurrence of certain host plants that are rather rare in the forest environment. In addition, in order for lepidopterans not targeted for treatment to be vulnerable to Btk, they must be in a larval stage and feeding. Thus not all 10 species are at a vulnerable stage in June. The negative impacts of using Btk are practically nil.

Product safety

As is shown by the available scientific information, Btk can be ingested by human beings or any other mammal and pass through their acidic stomach without being activated – i.e., without releasing any toxin. In 2008, in its re-evaluation decision concerning Bacillus thuringiensis insecticides, Health Canada’s Pest Management Regulatory Agency (PMRA) found “that products containing Bacillus thuringiensis do not present unacceptable risks to human health or the environment when used according to label directions.” As Btk is a naturally occurring bacterium, most humans are likely to come in contact with it and yet never experience the slightest symptom. No reports of infection or serious health problem have emerged following the medical monitoring of workers who were exposed during a spray program to considerably higher levels of Btk than are found in the environment. In addition, several independent studies have shown Btk to be non-toxic for mammals, birds, fishes, amphibians, other insects, etc.

Absence of environmental impacts

As various studies have shown, Btk formulations are specific to insects belonging to the order of Lepidoptera and thus are not a source of impacts on aquatic and terrestrial ecosystems. Thus, for example, no negative impacts are to be anticipated in relation to speckled trout, Atlantic salmon, white-tailed deer, hare or ruffed grouse. Quite to the contrary, these species stand to benefit from the positive impact deriving from the preservation of the forest cover. Since its founding in 1990, SOPFIM has carried out a program of environmental follow-up in respect of its Btk spray operations. These follow-up efforts have made it possible to better understand the behaviour of Btk in the environment and to assess its impact. The data thus gathered provide evidence that the concentrations found in the environment (i.e., in the water or soils) are well under the toxicity threshold established for various species in scientific literature. For example, concentrations found in water have been on average one million times lower than the lethal concentration (LC50) for the brook trout and the mallard duck, and have been 1,000 to 10,000 lower for more sensitive species such as crustaceans, aquatic insects and estuary species. In soils, the doses found following spray operations have been 1,000 to 10,000 times lower than the no-observed-effect level (NOEL) established for soil microorganisms. It is important to note that Btk does not bioaccumulate in the tissues or organs of living things. Thus it is safe to consume game, fish or berries gathered in forest areas. It is also important to know that droplets of the product deposited on foliage are rapidly degraded by microorganisms and the sun’s ultraviolet rays. If the insecticide in its active form is not consumed by the insects targeted by treatments, it will not persist for more than four days on foliage.

Adjuvants

Within the framework of its forest protection programs, SOPFIM uses only products whose active ingredient is Btk. All the products used have been registered with Health Canada’s Pest Management Regulatory Agency (PMRA). As the Btk bacterium constitutes the active ingredient, other products – called adjuvants or formulants – are included in the composition of the final formula. Aside from to the concentration and the strain of Btk used, the exact composition of each formulation remains confidential. For reasons of intellectual property protection, such information cannot be obtained either from the PMRA or the producers of insecticides. Before registering an insecticide, the PMRA ensures that the product presents no risk for human health and the environment. The impact of the various ingredients of the formulation is also assessed. Specifically, the formulants used in Btk insecticides are on the PMRA’s 4A and 4B lists, which designate, respectively, products of “minimal concern” and products of “minimal concern for a particular use.” For further details about the registration of Btk formulations, please visit the PMRA’s Website at: http://www.hc-sc.gc.ca/cps-spc/pest/index-eng.php.