In contrast, when people eat the same toxins, the toxins are not activated and no harm occurs. Each type of Bt toxin is highly specific to the target insect. Little to no direct toxicity to non-target insects has been observed. People are most commonly exposed to Bt through their diet, at very low levels. Exposure can also occur if you breathe it in or get it on your skin or eyes.
For example, this can occur while applying sprays or dusts during windy conditions. Since Bt is commonly found in soils, exposures not related to pesticides are also possible. Pets might be exposed to this product in treated birdbaths or water fountains. You can limit your exposure and reduce the risk by carefully following the label instructions. Bt is low in toxicity to people and other mammals. Several studies have found no evidence of sickness or infection as a result of exposure.
However, some products with Bt have caused eye and skin irritation. In one study, rats breathed in very high doses of concentrated Bt. Some had runny noses, crusty eyes, and goose bumps. Others were less active or lost weight.
In another study, people were surveyed before and after aerial applications of Bt. Most people were not affected. However, some people with hay fever reported certain symptoms. Seasonal factors, such as pollen, may have contributed to some of the effects. Scientists also evaluated whether Bt can cause allergic reactions. Researchers found that farmworkers exposed for one to four months did not experience any problems related to their airways, nose, or skin.
However, further exposure showed evidence of an immune response and the potential for skin allergies to develop. When eaten, Bt is confined to the gut. It does not reproduce, and the toxin is broken down like other proteins in the diet. Bt leaves the body within 2 to 3 days. If breathed in, Bt can move to the lungs, blood, lymph, and kidneys. Bt is then attacked by the immune system. Levels of Bt decrease quickly one day after exposure. No data were found on the carcinogenic effects of Bt in humans.
However, in one animal study, rats were fed very high doses of Bt for 2 years. No evidence of cancer was observed. In a 2-year study, rats were fed high doses of Bt daily. Female rats had lower body weights. However, no evidence of an infection was found. Bt is only activated in the alkaline environment of the insect gut, compared to the acidic environment of human stomachs.
Death will occur, primarily by starvation, in about 2 to 5 days. It is highly selective, and only kills certain insects. It does not kill most beneficial insects such as lady beetles and parasitic wasps. There are many strains of B. Some of the strains include:.
Agricultural Experiment Station. Commercial Horticulture. Environmental Conservation. Soil and Plant Nutrient Testing Laboratory. North American Aquatic Connectivity Collaborative. And beneficial insects — busy grazing on other insects and not plants — are likely to be unaffected by the bacteria. Bt will only kill insects that eat the toxin and are susceptible to it.
This is not a toxin that will kill on contact like most insecticides. Once eaten, the toxin affects a specific switch in the stomach — like a lock and a key.
This switch a receptor activates a reaction that makes holes in the stomach. It can take the insect hours or days to die. They are probably on their deathbeds. Bacillus thuringiensis kurstaki Btk is the best known and most widely used strain of Bt.
It kills the larvae of many types of moths and butterflies. This means that you can control most caterpillars with Btk. Monterey Btk Liquid via Arbico Organics.
Other caterpillars commonly controlled by Btk include the European corn borer, tent caterpillars , gypsy moths , and other forest caterpillars. There are even formulations designed to control Indian meal moth larvae in stored grain.
Several Btk formulations are available from Arbico Organics. Another strain of Bt, Bacillus thuringiensis aizawai Bta kills the larvae of wax moths in honeycombs. Fortunately, there is a strain of Bt that controls the larvae of many biting flies and mosquitoes! Bacillus thuringiensis israelensis Bti is commonly used by governments or non-governmental organizations to control mosquitoes on a large scale.
For example, the World Health Organization switched to using Bti to kill mosquitoes as part of its anti-malaria campaign rather than use chemical pesticides. You can buy Bti from Arbico Organics to kill mosquitoes on your property.
Mosquito dunks are a very popular product to kill these creatures in your water garden or rain barrels. Bti is very effective against Aedes and Psorophora mosquitoes. However, if you are trying to kill Anopheles or Culex , you will need to use greater amounts of this insecticide. As far as flies go, you can use Bti to kill black flies but not houseflies, blow flies, or stable flies.
You can also use some strains to control the larvae of fungus gnats in greenhouses or mushroom production.
In this case, you would apply the Bti as a drench to the soil for plants or culture media for mushrooms. You may or may not know that beetles comprise the largest number of species in the world, and there are more than , of them!
Fortunately, most of them are not garden pests. However, the Bt strains available only affect a few types of beetles. Some of them are major pests, though. The bacteria to use to control beetle larvae are either Bacillus thuringiensis san diego or Bacillus thuringiensis tenebrionis.
Beetles that can be controlled include the Colorado potato beetle , elm leaf beetle, and willow leaf beetle. First, make sure you have the right strain for the pest you want to control! You should also make sure that the insect will be in its larval stage when you apply the Bt. You will have better control if the larvae are small. If you treat larger larvae, they will eat more of the plants and cause greater damage. Also, they may morph into the reproductive phase and become insensitive to the toxin.
And avoid high pH water! The spray will be more effective if you add a spreader or sticker to the tank mix. Use the spray within 12 hours of mixing. Make sure that you are spraying both the top and bottom surfaces of the leaves. While it can survive for years in the ground if adsorbed to soil particles, Bt is rapidly inactivated by the UV radiation in sunlight. Many people spray their plants in the evening, so the toxin can work overnight before being inactivated by the sun the next day.
The bacteria are sensitive to temperature and must be stored at F. Do not expose the bacteria to hot or cold temperatures, which can kill them. Bt has tested extremely well when examined for toxicity or the ability to cause cancer in animals — even at extremely high doses. This microbe does appear to be truly safe for humans — even when eaten. Human stomachs are acidic, not alkaline, so they digest the Bt toxin. However, some products are used in the form of a dust, and there have been a few instances of allergic reaction to the dust when the product was applied.
Just to be safe, you should wear gloves, long sleeves, and trousers when you apply the microbial insecticide. And then wash thoroughly afterwards. Like any pesticide, the targets of Bt can develop resistance, although this rarely happens.
The diamondback moth, a pest of cabbage and other cruciferous plants, is the primary example of an insect that has developed resistance in the field. If you use Bt on your farm, the EPA will require you to take some steps to prevent resistance. One way is to alternate its use with synthetic insecticides. Another is to rotate your crops. Since different kinds of insects feed on different crops, you would be using a different type of Bt.
The large variety of Bacillus thuringiensis strains available enables gardeners, farmers, and mosquito control experts to control an array of insect pests. Since the strains are highly specific to the insects targeted, residual effects against other organisms are not a concern.
The widespread usage of Bt has been a boon to farmers and to people who are now sprayed with these bacteria to kill mosquitoes instead of DDT! See our TOS for more details. Uncredited photos: Shutterstock. Now that she lives near Santa Barbara, California, she is delighted that many of these grow right outside!
Fascinated by the childhood discovery that plants make chemicals to defend themselves, Helga embarked on further academic study and obtained two degrees, studying plant diseases as a plant pathology major.
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