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Home > Plants, Pests & Pest Control > Pest Management > Gypsy Moth Program > Treatments > Questions and Answers about Gypsy Moth and Btk

Questions & Answers about Gypsy Moth and Btk


Invasive insects, like the gypsy moth, pose a serious threat to the economy and environment of Minnesota. Without treatment, a population can get out of control and defoliate large sections of forest. Each time the Minnesota Department of Agriculture (MDA) proposes to treat gypsy moth, we must weigh the trade-offs and carefully consider all potential impacts. All of this is done with the highest regard for the health and safety of all residents. It is critical that sound information and reputable science be used in the discussion.

This site will be updated as new questions arise.

Please select a heading to learn more:

    • Based on careful review, the MDA uses the bacterium Btk, formulated in the product Foray 48B, for gypsy moth control.

      What is Btk?

      Bacillus thuringiensis kurstaki (Btk) as a naturally, occurring bacterium that is found in the soil. You may come into contact with it on a daily basis.

      How might I be exposed to Btk?

      People are exposed to Btk through contact with soil in the natural environment or through their diet, at very low levels. If you eat fresh fruits or vegetables, you probably have already ingested this bacterium. It is commonly used on commercial and organic food crops.

      Is Btk safe?

      Btk has a proven safety record with people, pets, birds, fish, livestock, and other insects such as bees; and has been registered and re-registered many times by the Environmental Protection Agency (EPA) for use in the U.S., to use on more than 200 food and fiber crops.

      What is Foray 48B?

      Foray 48B is the commercial product containing Btk. The inert, or inactive, ingredients used in Foray 48B are certified organic food-grade ingredients and contain no petroleum solvents. The product is certified organic by the Organic Materials Review Institute (OMRI). The Foray 48B Btk is not genetically engineered and the product is gluten free.

      I have read several accounts on the Internet of people suffering adverse health effects after Btk treatments. What about that information?

      Some people have reported mild skin reactions or mild eye, ear, and nose irritations after Btk treatments. Others have reported mild hay fever reactions. Health officials have studied these reports extensively and have not been able to determine if the reactions were caused by Btk or by pollens, molds, or dust generated during the treatments, or were unrelated to Btk treatments. The following are two cases often cited from the Internet.

      A study of an entire community in New Zealand was done for 2002 application of Foray 48B. Surveys of 292 study participants about their own symptoms and their self-perceptions of their health were conducted before and after the sprays; there were multiple applications of Foray 48B. Among the findings: there were significant increases in the rate of reported throat and gastrointestinal symptoms, and for sleep problems, following the sprays. Yet symptoms of exposure are quite general, and are often the same as those from other causes such as flu or food poisoning. The study authors cautioned that these self-reported symptoms were not necessarily confirmed by healthcare providers. Also, most participants in the New Zealand study reported their health (and that of their children) were not affected by the spray program, nor was there any reported increase in visits to either medical practitioners or alternative healthcare providers. 

      There have also been concerns that aerial sprays of Btk-based pesticides, such as Foray 48B, could impact vulnerable populations in the spray zone. Canadian researchers explored this issue during a 1999 application of Foray 48B over Vancouver Island. The lung symptoms and breathing capacity (lung function) of 29 children with asthma living in spray zone were compared to those of 29 children with asthma living outside the spray zone. Measurements, as conducted by parents, were done before and after the spray period. There were no differences in asthma symptom scores between either groups, neither before nor after the spray. There were there no significant changes in measured lung function, as reported by parents of study participants, after the sprays.

      Public health officials state Btk is not a public health risk.

      Is there a concern for 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 weakened immune systems or serious food allergies may choose to avoid any potential for exposure by staying indoors during and at least 30 minutes after the treatment, or leaving the area during the application. 

      Will Btk and Foray 48B cause cancer?

      Given the long history of use and the knowledge that regulatory and public health officials have about Btk and Foray, there is no reason to suspect that either Foray or Btk is carcinogenic.

    • Will the product harm humans, other mammals, fish, birds, bees or other insects?

      No, Btk is not toxic to humans, mammals, birds, fish, honeybees or many beneficial insects. Btk needs to be ingested (eaten) to be effective and that the toxic substance is only released under alkaline conditions present in the stomach of insects. This alkaline condition is not present in the stomachs of humans, mammals, birds, or fish which is why the Btk does not affect them.

      Btk is so specific to only certain moths and butterflies that it is an approved control product for use by certified organic gardeners.

      Will more treatments be necessary?

      Minnesota first used Btk for gypsy moth in 1984. Since then, the state has treated 37 sites. Only one area has need to be retreated. Why was a retreatment needed? It is likely the original treatment area was too small to eradicate all the gypsy moths. The MDA strives to find the right balance when drawing treatment areas.

      We do our very best to design our management blocks as small as possible yet large enough to avoid missing the population and having to conduct a second year of application. In addition, we want to treat the population as quickly as possible to avoid the population from expanding and thus resulting a much larger treatment area in following years.  

      Will the product harm my vehicle, home, and other items outside?

      The spray residue is not harmful to humans, animals or outdoor structures. The spray can be easily washed off. It will show more readily on dark colored vehicles and it can be washed off. If left in the sun for a few days without washing, the spray deposit on vehicles may have to be rehydrated in order to remove it. Take an old bath towel and soak it in sudsy water and drape it over the vehicle for a few minutes. This will help soften the spray deposit and it can be removed. More ‘elbow grease’ may be required if the spray deposit is left on the vehicle for several days.

    • How long will the application take?

      Depending on the aircraft, applications will likely take approximately 2-3 hours and will begin shortly after sunrise, as early as 5 AM. The aircraft will be ~ 50 feet above the tree tops; not the ground. A second application will occur 7-10 days following the first application.

      How will I know when applications will begin?

      Exact dates and times depends greatly on weather conditions and insect development. Notification will be made 7-14 days in advance of any treatment through various media outlets, including local newspapers, TV and radio. Residents within the block will receive a reminder postcard notifying them about the upcoming application. MDA staff will be on-site to overs the application. The MDA’s Arrest the Pest Info line, 888-545-6684 (MOTH) will be updated with treatment information frequently. You can also find information on treatment by following the MDA on Twitter.

  • Contact: Arrest the Pest at 888-545-6684 (MOTH) for the most up-to-date information.

    MDA Contact

    Arrest the Pest
    888-545-6684
    gypsy.moth@state.mn.us