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BTK Insecticide FAQs

Questions and Answers about Gypsy Moth Spraying and Your Health

What is Btk?

Bacillus thuringiensis (Bt) exists as bacteria in soil in the natural environment. There are many strains of Bt, several of which are used as biological pest control agents on edible crops, including organically grown foods. The toxicity of the different Bt strains is insect specific. For example, Bacillus thuringiensis kurstaki (Btk) targets moth larvae whereas Bacillus thuringiensis israelensis targets fly larvae. The larval stage of life is most susceptible to Bt toxicity due to the active feeding behavior of larvae. When gypsy moth larvae eat vegetation treated with Btk, a toxin is released in their stomach. This toxin eventually starves or poisons the insect.

What is Foray® 48B?

Foray® 48B, EPA Registration No. 73049-427, is certified by the Organic Materials Review Institute (OMRI) as an organic product. The product contains 12.65% Btk as the active ingredient. In addition to the bacterial ingredient, Foray® 48B may contain “inert or other” ingredients, including binders that help the spray stick to vegetation after it is applied. Foray® 48B may also contain carriers such as: water, carbohydrates, proteins from grain sources like corn or soybeans, stabilizers for acid control, preservatives and wetting agents. The EPA assesses the toxicity of "inert or other" ingredients, please refer to the EPA website on Pesticide Inert Ingredients for more information.

Are there any human health risks associated with the gypsy moth? 

Gypsy moths are mainly a threat to vegetation. When the number of the caterpillars is very high, some people may experience allergic reactions. The gypsy moth caterpillars have spiny hairs which may cause welts or rashes, lasting up to 4-5 days. Population levels of gypsy moths in isolated infestations, such as those we have in Oregon, do not normally pose any health risks.

Can Btk make people sick?

People are exposed to Btk through contact with soil in the natural environment. If you eat fresh fruits or vegetables, you probably have already ingested this bacterium. It is commonly sprayed on commercial and organic food crops. The toxicity of Btk has been researched in laboratory studies with animals and by monitoring people in the U.S., Canada and New Zealand where Btk has been used for more than 25 years.

Evidence from scientific literature:
  1. Eighteen human volunteers suffered no illness from eating 1 gram of Btk each day for 5 days.
  2. Five human volunteers suffered no illness from inhaling 100 milligram of Btk each day for 5 days.
  3. Bt has been used for moth control since the 1950's. There is little evidence that a causal relationship exists between health effects and exposure to Bt among human populations within aerial spray areas.
  4. Researchers injected Bt into the bloodstream of mice with compromised immune systems for 27 days and reported no deaths.
  5. Laboratory animals exposed to Btk by feeding, breathing, injection through the skin, and application into skin abrasions were not seriously harmed by exposures.
Reports of harmful effects from Btk include:

  1. A corneal ulcer developed after a farmer splashed Btk into his eye. This healed after medical treatment.
  2. Rabbits given droplets of various strains of Bt in their eyes experienced temporary eye irritation.

It is unlikely that indirect exposure to Btk will result in adverse health effects in non-target organisms, including people. People working in occupational settings, directly exposed to Btk, for long periods of time have had mild skin irritation or short term breathing problems. After a thorough review of the toxicity of Btk products, including both active and inert ingredients, the U.S. EPA, Health Canada, the World Health Organization, and many other groups categorize Bacillus thuringiensis as a least toxic method of pest control.

Is there any information about Btk and people's health in Oregon?

Bacillus thuringiensis has been applied as an insecticide on many occasions in the United States (including Oregon), Canada, New Zealand and elsewhere over the last 25 years.

The Center for Health Protection and county health departments conducted public health tracking of illnesses possibly related to gypsy moth spraying during previous eradication programs in Lane County in 1985-1986 and the Portland Metropolitan area in 1987 and 1992. The tracking included reports from doctors and information on hospital emergency room visits. There was no increase in illnesses among people living in spray areas that could be linked to Bt spraying.

In 1986, the Center for Health Protection conducted a special study of health complaints related to Bt spraying. No unusual patterns of illness complaints were identified. Cultures (blood, urine, throat, wound, etc.) from patients in the spray area were evaluated to determine if Btk was present. When Btk was found in the culture, a patient's medical record was reviewed to determine whether the Btk had caused illness. The Public Health Division found 58 patients with cultures that grew Btk. In 55 of these instances, it was determined that Btk was probably a contaminant of the culture, not the cause of illness. Additionally, and because Btk is a native organism in the environment, without baseline data it is impossible to know if Btk was present in the body prior to the application. In three patients, there was some evidence that the positive cultures resulted from exposure to Btk but it could not be conclusively determined whether Btk was a contaminant of the culture or the cause of illness. All three patients had pre-existing medical problems.

In 1992, the Multnomah County Health Department and the Center for Health Protection jointly monitored a population in the spray area for signs of ill health effects. A total of 66 calls were received from people living in the spray zone, who reported symptoms which they thought may have been caused by the Btk spray. Most of the symptoms reported were minor and when investigated were found not to be clearly associated with the spray. No positive cultures for Btk infection were found.

What about people with weakened immune systems and people with allergies?

Although we don't have evidence that Btk will affect any given group of people, individuals with a compromised immune system may choose to avoid any potential for exposure by leaving the spray area during the application. If you or someone in your home is concerned and cannot stay indoors or leave the area during the application you might consider speaking to a health care provider.

Foray® 48B product may contain residues of grains, food additives, or preservatives. If you have serious allergies to these you might consider contacting your health care provider. Your health care provider might choose to consult with the manufacturer of Foray® 48B (Valent Biosciences – 1-800-323-9597) to discuss medical concerns about the "inert or other" ingredients.

What should I do before and during the spraying?

Even though Btk is not expected to result in adverse effects, we recommend that people stay indoors during the application. The Department of Agriculture should provide advanced notification to let you know when spraying will occur. If you or someone in your home is concerned about the application due to a medical condition please consult with a health care provider.

Depending on the level of actions you choose to take, we recommend the following:
  • Closing windows and doors and shutting off HVAC systems that distribute air from the outside into your home.
  • Covering playground equipment, sandboxes, benches, toys, pet dishes, and lawn chairs before the application, or hosing them off afterward.
  • Staying indoors during and for at least 30 minutes after spraying to allow droplets to settle and adhere to vegetation.
  • Waiting until the spray has dried before touching vegetation treated during the application.
  • Washing exposed skin with soap and water if direct contact with the spray droplets occurs. If you are outside at the time of application and the spray droplets get into your eyes, flush with water immediately and contact the Oregon Poison Center at 1-800-222-1222 for further medical advice.

What if I have more questions?  

For more information about Btk, contact the National Pesticide Information Center (NPIC), based at Oregon State University, by calling 1-800-858-7378 or view their website and Btk Fact Sheet

If you have been exposed to Btk and you have concerns about possible health effects, wash the affected area and contact the Oregon Poison Center at 1-800-222-1222. If you have serious allergies to food or food preservatives, your health care provider may consult with the manufacturer, Valent Biosciences at 1-800-323-9597. For further information on Btk, call the Oregon Department of Agriculture at 503-986-4635.