Btk Questions and Answers

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Mechanical, cultural, biological, and chemical strategies have been employed to eradicate gypsy moth since it was first introduced in North America.

1. Mechanical methods include egg mass scraping and the use of tree bands as a barrier that excludes larvae from trees or as a harborage area to aggregate, collect, and destroy larvae.

2.  Cultural practices are achieved through education and outreach to, or regulation of, affected communities and stakeholders.  The goal of this strategy is to elicit behavioral change that assists eradication. Restricting movement of gypsy moth out of infested areas or into non-infested areas is key for successful eradication and can be achieved with education or regulation, usually in the form of quarantines.

3.  Biological control makes use of naturally occurring organisms like bacteria, viruses, predators, and parasites or insect behavior to impact unwanted pests like gypsy moth. 
Examples of biological control used for gypsy moth eradication include:
  • Sterile insect technique: This technique consists of an aerial release of a large number of sterile male gypsy moths; reducing the chance that female moths will mate with fertile males. The result is progressively fewer and fewer fertile egg masses being produced, and eventual elimination of the population.
  • Gypsy moth virus (Gypcheck®). This is a nucleopolyhedrosis virus which occurs naturally and is specific to gypsy moth. Gypcheck® is a product made from the gypsy moth nucleopolyhedrosis virus.
  • Bacillus thuringiensis var. kurstaki (Btk). This is a naturally occurring soil bacteria. Formulations of this bacteria are effective against caterpillars of many species of Lepidoptera (moths and butterflies) including gypsy moth.
  • Predators and parasites are only occasionally used in eradication efforts. They are most often employed to reduce the size of an established population or maintain a population at a low level.  Dozens of different predators and parasites of gypsy moth have been released in North America.
4.  Chemical control options have been used in many parts of the country since gypsy moth was introduced.
Examples of chemical control options include:
  • Mass trapping: This treatment technique consists of deploying large numbers of traps baited with synthetic gypsy moth sex pheromone used to attract the male gypsy moth and prevent them from mating with females, thereby causing a population reduction.
  • Mating disruption: This treatment technique consists of applying tiny plastic flakes or beads containing a synthetic gypsy moth sex pheromone. The pheromone confuses male gypsy moths and prevents them from locating and mating with females.
  • Insecticide application: Ground and aerial application of insecticide has been used to support gypsy moth           eradication. Chemical insecticides include Diflubenzuron (Dimilin®) and Tebufenozide (Mimic®). These are insect growth regulators that disrupt the ability of insect larvae that produce an external skeleton, containing chitin, to molt from one stage to another.
WSDA uses an Integrated Pest Management approach relying on the best tools available for a given situation.  Cultural control in the form of education and outreach is a large component of the WSDA approach and eradication efforts are guided by robust monitoring and delimitation program.  The information from moth captures is used to determine the best approach.  

When reproducing populations of gypsy moth have been identified in Washington State, the most commonly used technique has been application of the biological insecticide Btk targeting the second larval stage of the gypsy moth.  Delivery methods have included ground spraying and aerial application using helicopters or fixed wing aircraft.
Yes. The main disadvantage is that Btk breaks down quickly in the environment and the same treatment area might require three to five applications in one season to be effective.  Application windows for this product are also extremely narrow, and the methods used require suitable weather conditions for a favorable result, making the timing of application a challenge.  A second disadvantage is that although Btk has virtually no impact on humans, other mammals, birds, fish, and bees, it is detrimental to the caterpillars of most moth or butterfly species that feed in treatment areas.
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. Public health officials state Btk is not a public health risk.
Remain indoors for at least 30 minutes after a spray application, particularly those with leukemia, HIV, respiratory disorders, other immune deficiencies, those receiving radiation or chemotherapy, those with allergies, and those prone to respiratory irritation. Children should wait until moisture from the spray and dew has dried on grass and shrubs before playing outside. If you come in contact with the wet spray, wash with soap and water.
State and federal law prohibits the release of the information without the manufacturer’s release. The rationale for this law is that other manufacturers could then replicate the product. However, the law allows for public health officials -- after signing a non-disclosure agreement -- to review all ingredients of Btk and then comment in general terms about the safety of the insecticide. This has been done repeatedly in the past in Washington before Btk treatments. Local public health officials have always reported Btk doesn’t represent a serious public health risk.
Mass trapping        
  • Advantage: Target specific, and pinpoints center of population.
  • Disadvantage: Not a proven eradication method.
Mating disruption
  • Advantage: Target specific.
  • Disadvantages: Not a proven eradication method; effectiveness cannot be evaluated as trapping treatment areas is not possible; and effective adjuvant for mating disruption not registered in Washington State.
Sterile insect release
  • Advantage: Target specific; minimal impact on environment.
  • Disadvantage: Very expensive, requires mass rearing, requires repeated treatments over a span of yeras.
  • Advantage: Target specific.
  • Disadvantage: Not a proven eradication method; most effective with high populations, not low populations.
  • Advantage: Proven eradication method.
  • Disadvantages: Product has a long residual, remaining in environment for long period; and toxic to many non-   target insects.
Before treatment begins, environmental reviews (called SEPA for the state and NEPA for the federal government) must be completed. The public has the opportunity to comment in writing as part of the environmental review process. Comments are reviewed and taken into consideration before the eradication plan is finalized.
Btk will not harm bees, birds, fish or other aquatic life. Birds or fish that might eat a caterpillar that has consumed Btk will not be harmed. Btk only affects caterpillars that are feeding during or within a couple of days of application. Btk is effective against moth and butterfly caterpillars due to the alkaline (or high pH) of their guts. This condition allows for Btk to be broken down and produce a toxin that kills the caterpillar, but not other organisms. 
Only the caterpillars of moths and butterflies that are feeding at the same time as the gypsy moth caterpillar (or when Btk will be applied) will be impacted. However, these moths and butterflies will quickly repopulate the area from outside the treatment zone - usually within a couple of years. If gypsy moth is allowed to establish in an area, its caterpillars will quickly ravage the vegetation that these native moths and butterflies depend on. This would force the native moths and butterflies permanently out of the area.

Monarch butterflies are not likely be impacted in Washington from Btk treatments.  First, Washington - especially Western Washington - is not a primary migration area for the monarch butterfly due to rarity of suitable host material (milkweeds) and unfavorable climate conditions for this species. Second, even if monarch butterflies arrive in Washington, the have a much different life cycle than the gypsy moth. Caterpillars only begin feeding in late June in Washington, after any Btk applications have degraded. Read more on our Monarch and the Moth blog.
No. Btk is a naturally occurring soil bacteria that has been used for decades to control caterpillars. Btk is not genetically modified. The formula WSDA typically uses for gypsy moth treatments, Foray 48B, is certified for use in organic agriculture or gardening. Certified organic products cannot contain genetically modified organisms (GMOs.) Read more in our blog Gypsy Moth Treatments and the GMO Myth.
There is nothing in Foray 48B that will cause damage to automobile finishes. This product is formulated to stick to the surface of leaves when it dries. Therefore, it is easiest to remove from any surface while it is still wet. To remove dried Foray 48B from any surface, simply soak the dried droplets with water and then sponge or wipe with a soft cloth. A cleaning product normally labeled for car washing may be needed if the dried spray has been on the surface for a while. The sooner the surface is cleaned, the easier it will be to remove the spray droplets.

If the automobile’s paint is old, oxidized, and/or severely weathered, Foray will adhere to this porous surface; it will be more difficult to remove. A large bath towel may be soaked and placed upon the painted surfaces for several minutes to allow the Foray deposits to become rehydrated. This will make the spray deposit easier to remove. In extreme cases, several soakings with a wet towel may be required.