“Btk is a naturally occurring organism and it is found in the soil and on plants around the world.”
- What is Btk and how does it work?
- Btk’s Impact on the Environment
- Btk’s Impact on People and Pets
- The Government of Newfoundland & Labrador’s Position on the Use of Btk
- References
Newfoundland’s forests are an important resource. Many of us enjoy spending time n the woods camping, hiking, fishing or hunting. Others make a living from the forests through tourism or from the responsible harvest of trees for the pulp and paper and the saw milling industries, building homes or for firewood. A healthy forest ecosystem contributes to healthy forest wildlife, ponds , streams, air and soil. A healthy forest benefits us all.
The hemlock looper and spruce budworm are common insects in Newfoundland’s forests. When their populations are low, they cause little damage to the trees. At low population levels, the insects provide an important food source for other forest wildlife. However, when their populations suddenly get very high, they can cause considerable damage to the forest affecting not only the trees, but parks, ponds and streams too. When large areas of trees are killed by the insects, it directly affects everyone who makes a living from or just enjoys spending time in the woods. Widespread tree death will also affect forest wildlife.
Forest resource managers must act quickly and respond to protect the forest from widespread damage from high insect populations. it is important to protect the integrity of the forest ecosystem by maintaining a balance in the ecosystem. One of the ways that the government and the pulp and paper companies protect the forest from hemlock looper or spruce budworm outbreaks is through the use of biological insecticides like Bacillus thuringiensis kurstaki, more commonly known as Bt or Btk. Bt is found in insecticide formulations such as Foray.
What is Btk and how does it work?
Bacillus thuringiensis var. Kurstaki (Btk) is a naturally occurring bacterium that can kill larvae (caterpillars) of some lepidopteran insects (butterflies and moths), including the gypsy moth, spruce budworm, and hemlock looper. Btk is commercially available as a biological insecticide and it is used in pest control programs in forestry, agricultural and urban settings around the world.
Btk is one of several varieties of Bacillus thuringiensis available. Bt varieties aizawai and kurstaki are active against lepidopteran larvae. Because of differing characteristics between varieties, it is important to identify the variety specified during discussions about Bt. Btk is most commonly used to control defoliating caterpillar pests. Bt israelensis and sphaericus are active against mosquito and black fly larvae, and Bt tenebrionis attacks Colorado potato beetle larvae.
In order to kill insects, Btk must be eaten. The Btk bacteria produces a toxic poison formed as a crystal which is released inside the gut of the insects like the Eastern Hemlock Looper. Only these insects (lepidopteran larvae) have the alkaline gut required for the Btk poison to be activated. It is the poison crystal, and not the bacteria, that actually kills the insect.
The caterpillars stop feeding almost immediately after eating leaves covered with a Btk spray; however death may take a few days.
Btk is effective in controlling the hemlock looper, but as it must be eaten, it must be applied when the insects are feeding most actively and when they are most susceptible to its toxins. It takes very little Btk to be effective; in fact 2 to 3 litres is sufficient to cover a hectare of forest. However, two applications may be required to provide good control as not all the pest caterpillars may be actively feeding at any given time. Additionally, the looper caterpillars are actively moving around in the canopy of the forest and it can be challenging to control the pest with Btk.
Btk’s Impact on the Environment
Bt is a naturally occurring organism that can be found in the soil and on plants around the world. Btk is produced commercially by fermentation in large vats, similar to the production of alcohol or antibiotics. Btk needs the conditions provided by fermenters or vats (ample food, heat, moisture) to reproduce on a large scale. since these conditions do not occur in nature, Btk cannot be reproduced naturally in sufficient quantities to act as a natural control for forest pests.
Btk has been extensively studied; in over 25 years of use, no significant environmental impacts have been observed. Btk will kill other lepidopteran larvae, but these may not be as sensitive as the hemlock looper to Btk. Most often these other caterpillars are not at a susceptible stage or they are not feeding at the time that Btk is applied. As a result, Btk applications, when timed for the control of the hemlock looper, do not have a significant impact on other caterpillar species.
Btk does not kill other types of insects, such as honeybees, insects predators or parasites. Btk has no impact when eaten by fish, earthworms, amphibians, birds, mammals or humans; non of these organisms have the alkaline gut necessary to activate Btk.
Bird species that eat insects will feed on hemlock looper caterpillars when they are available. Of course, if the number of caterpillars are reduced due to a Btk spray, the birds will have to feed on other insects. Studies of certain insect eating bird species conducted during the height of a looper or budworm outbreak suggest that the looper caterpillars are only a part of their diet, and only for a few weeks. the birds quickly adapt to eating other insects when the looper larvae are gone.
Looper defoliation can kill many trees and cause significant adverse changes in the forest environment for all life forms that depend upon the forest for survival.
As Bt is sensitive to sunlight, it breaks down quickly in the environment. Several days of sunlight or a heavy rain can render a Btk spray ineffective.
For further information and literature on the impact of Btk on the forest environment, see the attached list of references.
Btk’s Impact on People and Pets
Btk is considered a safe biological insecticide. The same product used in forest applications is also registered for use on fruit trees, berries, and even for vegetables grown in greenhouses. As required by Health Canada, extensive oral, feeding, inhalation and intravenous animal studies have been conducted with Btk. No evidence of any poisonous, infectious or disease-causing effects were found. Very mild, temporary skin irritation, and moderate, temporary eye irritation was observed when Btk was accidentally applied directly onto the skin and into the eyes of ground spray workers. These effects were completely reversible and were not reported by bystanders or any others who were exposed to Btk in a normal aerial application over an urban environment.
Health Canada and the U.S. Environmental Protection Agency have determined that Btk may be applied up to the harvest date on all of the crops on which it is registered for use. There is no required interval before re-entering a sprayed forest. this is based on extensive testing of Btk to determine both the short-term and the long-term effects on humans and warm-blooded animals.
Bt is a common bacteria found in soils throughout the world. People are exposed to Bt and many other microbes everyday. many of the microbes we encounter, including Btk, do not produce any poisons which affect humans.
Btk and other common bacteria are frequently found in blood, urine and other samples from healthy people. It has been shown that the presence of Btk in patient specimen samples, as it is not infectious, is not medically significant.
Individuals with pre-existing allergies, asthma or hypersensitive individuals, especially those sensitive to normal exposure to soil or smoke and pollutants, could feel some temporary effect. However, exposure to a Btk spray program is not likely to result in the development of new allergies, asthma or other hypersensitive reactions.
The exposure level to Btk from an aerial spray program is very low in comparison to the levels applies in safety and health related testing. Even at the higher levels used in tests, Btk has been shown to be safe. that safety has been confirmed again and again over 25 years of use in urban and rural applications.
A solid record of safety and health has been amassed over this time.
The Government of Newfoundland & Labrador’s Position on the Use of Btk
The Government of Newfoundland and Labrador recognizes the importance of a healthy forest to both the environment and the economy. Accordingly, government supports responsible and safe efforts that protect forests. The biological control agent bacillus thuringiensis var. kurstaki (Btk) has been used effectively to control outbreaks of the Eastern Hemlock Looper and the Eastern Spruce Budworm.
The decision to use Btk to control outbreaks was made only after careful review of the existing information on the health and environmental effects associated with spray programs using the control agent. There is an absence of credible reports showing environmental or health problems even after long-term, widespread Btk spray programs throughout North America. Furthermore, the Department of health supports the position of Health Canada that Btk does not pose a risk to people.
Government participates in programs to reduce insect populations, minimize defoliation and keep trees alive long enough for natural factors (parasites, viruses, fungal diseases and other predators) to eliminate the outbreak. I light of the health and safety record associated with over 25 years of worldwide use, the provincial government supports the continued use of Btk to protect our valuable forests when threatened by either the Eastern Hemlock looper of the eastern Spruce Budworm.
References
There are numerous references on the use of Btk to protect forests and crops. A suggested short list includes:
Noble, M.A., P.D. Riben and G.J. Cook, 1992
Microbial & epidemiological surveillance program to monitor the health effects of Foray Btk spray. Ministry of Environment, Province of British Columbia, Vancouver, BC
Otvos, I.S. and S. Vandervein. 1993
Environmental report and current status of Bacillus thuringiensis var. kurstaki use for control of forest and agricultural pests. Forestry Canada and Province of British Columbia Ministry of Forests, Victoria, BC
Reardon, R., N. Dubois and W. McLane. 1994
Bacillus thuringiensis for managing gypsy moth: A review. USDA Forest Service, National Center of Forest Health Manage, Morgantown, WV