Bacillus thuringiensis (Bt) is a species of bacteria that can be found in soil throughout the world. Because it occurs naturally, it is a popular choice in the effort to control mosquitoes, especially since it is not toxic to humans. Now that you know what Bacillus thuringiensis is, we’ll explain how to use it safely and effectively to keep mosquitoes at bay in your yard.
How Bt Works
- Spores are eaten by a mosquito.
- The meal makes its way to the mosquito’s midgut.
- A Bt toxin is activated because of a mosquito’s high gut pH (9.0 to 10.5).
- Gut linings are damaged. Infection sets in.
- The mosquito dies of starvation.
A scientific note: Humans have guts with a low pH (acidic), so the toxin does not activate.
How to Deploy Bt on Mosquitoes
- Tablets: A product with the brand name “Mosquito Dunks” has been around so long (since the 1980s) that the term “mosquito dunks” is regularly used (even in government reports) for any Bt product that is dropped into standing water and dissolves, killing mosquitoes in the larval stage.
Mosquito dunks are known for their briquettes being doughnut-shaped. Similar products are also available commercially (for example, Mosquito Bits, Mosquito Bombs, and Microbe-Lift) and can be round, in pellets, or a liquid, among other things. These doughnut and granule forms are most popular for home use. - Airplanes, usually over bodies of water, including ponds, lakes, rivers, and streams. It is sometimes used to coat leaves.
- Trucks: The Bt is sent into the air and over water to kill larvae.
- Handheld sprayers, including backpack units and thermal foggers. A study found they work about the same.
- Drip or overhead irrigation systems deploy Bt directly onto the soil.
- Center-pivot irrigation systems are used, usually on large agricultural areas.
Dangers to People
Bt has not been found to kill people, but it has been found by the EPA to cause problems. The EPA points out that any chemical product can pose risks to people. One should make it a point to handle it carefully.
Exposure to Bt can produce:
- Skin irritation, sometimes a red rash
- Eye problems: Symptoms may include burning and itching or eyes that become watery.
- Nose and throat distress, including laryngitis
- Breathing problems similar to asthma or other lung problems
- Headaches
A pro’s tip: Exposure is known to occur when people attempt to apply a spray when there is wind, or even a noticeable breeze. Exposure can also occur if you don’t wash your hands after using it in any form, then eat, drink, or smoke. This is one reason why you should wear gloves, long sleeves, long pants, socks, and shoes when mixing and applying it.
Ingestion may cause:
- Diarrhea
- Fluid loss
- Blood in stools
- Low blood pressure
- Elevated blood sodium (hypernatremia)
Strains of Bt, even in residues, might aggravate pre-existing skin, eye, respiratory, and gastrointestinal conditions.
A pro’s tip: Bt can turn up in drinking water (say, from aerial spraying). People (primarily children) are also known to drink from backyard water fountains. Pets are known to drink from birdbaths (and backyard fountains) that have not been treated properly.
How to Be Safe While Using Bt
Follow these safety guidelines, especially if you’re using a liquid Bt formulation:
- Product label: Follow the label directions.
- Gloves: Wear them, and be sure they are waterproof.
- Goggles: To protect your eyes. And no, your eyeglasses aren’t enough.
- Respirator: Wear one when mixing Bt.
- Mask: Wear one if you don’t leave on the respirator when applying Bt.
- Protective clothing: Wear long sleeves, long pants, and shoes with socks.
Animals That Bt Controls
In addition to being used to control mosquitoes, Bt also is used to control:
- Other flies
- Beetles (Coleoptera)
- Black flies and other insect larvae
- Gnats: But use of Bt is not effective on mites.
- Lepidoptera (caterpillars of butterflies and moths), including the gypsy moth and the European corn borer
- Nematodes (roundworms that can be microscopic in size)
Is Bt Harmful to Birds?
Birds were not found to have suffered when fed Bt tenebrionis, israelensis, aizawai, and kurstaki strains.
What Are the Best Known Bacillus thuringiensis Strains?
Here are the most common strains of Bt and the insects they control:
- Bt israelensis (Bti): Mosquito, fly, and gnat larvae
- Bt aizawai and Bt kurstaki: Caterpillars
- Bt tenebrionis and Bt japonensis: Beetle larvae
- Bt san diego: Beetle larvae and other insect pests
Key Dates in Bt History
If you’re skeptical about using the latest insect-control products around your home and family, we’re here to help. Read through this brief history of Bt for a bit more background information on this larvicide and how it has been used in genetically-modified crops in recent years:
- 1901, a Japanese scientist isolated a bacterium from dead silkworm larvae.
- 1911, a German scientist isolated a related strain from dead Mediterranean flour moth larvae and named it Bacillus thuringiensis.
- 1938, in France, the first commercial insecticide using Bt was produced.
- 1958, Bt is made in the U.S. Production of Bt grows quickly to fight infestations.
- 1961, Bt-based products are registered with the Environmental Protection Agency.
- 1996, Bt crops (insect-resistant transgenic crops) started spreading around the world. Transgenic plants spread, too, another bit of genetic engineering to fight insect species, as well as specific insects.
- 2020, 83% of the cotton and 79% of the corn planted in the U.S. are genetically modified Bt crops.
FAQs
In 1959, 18 people agreed to eat 1,000 mg (0.035 ounces) of a pesticide containing Bt daily for five days. Every other day, five of the volunteers also inhaled 100,000 mg (3.5 ounces) of the product in powder form. The volunteers in this study did not have issues that would cause the product to be banned. Mice that were injected did have negative effects, including death.
A Bti briquet will last about 30 days, so experts recommend that you drop new ones in your roof gutters and other places with stagnant water every month.
If you spray it or sprinkle a granular product, you need to do it every other week.
No evidence was found that ingesting or breathing Bt could be linked to cancer in humans. In addition, cancer was not discovered in humans who ate Bt proteins.
Yes, they are, because of the way they live:
• Children put strange things in their mouths, don’t they?
• Children crawl on the floor, or play on it, and the floor is where yucky stuff lives.
However, the EPA has done studies that found children and infants are not at greater risk than adults after ingesting Bt. In one study, children living in an area that underwent heavy aerial spraying did not have more asthma or lung problems than children outside the area.
Bacillus thuringiensis (Bt) is a gram-positive bacterium of the soil. It is rod-shaped. It is part of the phylum Firmicutes and the genus Bacillus. It is a bacterium that forms spores. During sporulation, it produces a number of crystal proteins that have increased toxicity to insects.
Bacillus thuringiensis Cry and Cyt toxins are proteins that go after midgut epithelial cells by forming pores in membrane. Among this group of proteins, members of the 3-Domain Cry family are used worldwide for insect control, and their mode of action is a multi-step process.
A Call to Action
If you are interested in applying Bacillus thuringiensis, you can’t be casual about it. Review your options, make a decision, then act on it.
You can apply Bt on a do-it-yourself basis, but experts recommend that a proper mode of action may be to call in a professional. Contact Pest Gnome to connect you with a pro in your area.
Main Photo Credit: Dr. Sahay / Wikimedia Commons / CC BY-SA 3.0