Welcome to PestiBytes from the
National Pesticide Information Center at Oregon State
University Hi. I’m Colton, with the National Pesticide Information Center here to talk with you about Bacillus thuringiensis, which is also known as ‘Bt’. We’ll talk about what it is, how it works, and its toxicity. Bt is actually a group of closely related soil microbes. Each type of Bt makes a different kind of protein that is toxic to specific groups of insects. When these insects eat the protein, it changes shape, and attaches to the insect gut wall, creating holes in it. Soon after, these insect larvae stop feeding and they eventually die. In contrast, when people eat the same proteins, they don’t change shape and they don’t cause us harm. Bt is found in over 180 pest control products. These products generally contain a mixture of Bt toxins. Varieties are only effective for certain types of insects. For example, Bt kurstaki products are used on garden plants to control caterpillars. Products with Bt israelensis are used around water to control immature flies and mosquitoes. Additionally, some plants, such as corn, cotton, and potatoes, have been engineered to produce their own Bt toxins. This is done by copying certain pieces of DNA from Bt and putting them into a plant’s DNA. Plants use this DNA, like an instruction manual, to produce Bt toxins within its own tissues. That way, when insect larvae eat the plant tissues, they are exposed to the toxins. This form of genetic change in the plants can reduce overall pesticide spraying to control insects. And, when people eat these plants, the toxins do not work on us or cause us harm. In the environment, when Bt and its toxins land on surfaces, sunlight breaks them down quickly. They are also broken down by other microbes in the soil. However, breakdown is generally slower below the soil surface where it’s dark. In soil, Bt typically stays in the top several inches. There, it remains dormant until extra nutrients become available. In water, Bt is not known to reproduce. Now that you know a little bit more about what Bt is, let’s discuss its toxicity to people. Exposure to Bt can occur if you eat it, touch it, or breathe it in. Once inside your body, Bt does not reproduce, causing infections. Rather, most of it is broken down and rapidly leaves our body. The proteins that kill insects are also broken down. Bt is low in toxicity to people and animals. However, some Bt products can irritate the eyes and skin in dust form or at very high concentrations. In most studies where animals ate, breathed, or were injected with Bt, exposure did not cause any health problems. In a long-term animal study, eating Bt did not lead to the development of cancer. In one study, rats were fed high daily doses of Bt for two years. Some females did not gain as much weight as normal. However, in another study, human volunteers ate or inhaled and ate Bt for several days. None of these volunteers became sick. Looking for more in-depth information? Check out our fact sheet online, or give us a call. Remember, pregnant women and other folks can always reduce their risk by reducing their exposure to chemicals, including any pesticide. Also, while children may be more sensitive to pesticides, there are no studies showing that children are especially sensitive to Bt. Among wildlife, the toxicity of Bt is generally low. For example, Bt is low in toxicity to mammals, birds, fish, and shrimp. It also failed to cause infection. However, impurities produced with Bt can cause indirect toxicity to some non-targets. For example, depending on the Bt variety, toxicity to water fleas, an important part of the food web, ranges from low to high. Also, several varieties of Bt are low in toxicity to honey bees, but one variety is highly toxic to honey bees. There is little or no evidence of direct toxicity to many other non-target insects. Finally, let’s discuss some ways that you can keep your risk low. Because there is some level of risk to both you and the environment with pesticides, be sure to consider all of your options before you use a pesticide. For example, you can reduce breeding places for mosquitoes by replacing birdbath water daily, and eliminating standing water from other areas around your home. If you have decided to apply a product, always follow the label instructions. In the case of spraying plants in your yard or garden, think about applying during calm weather and keeping others inside until the product has settled out of the air and dried on surfaces. For water treatments, make sure that children and pets are unable to access the product. Thanks for watching! Remember you can call us, or check out our website, to dig deeper.