What is it and how does it work?
BT is a soil-based bacterium that occurs naturally in the environment. Nationally, BT is the most commonly used control against gypsy moth infestations in an urban setting. The mode of action of BTR is simple. The bacterium produces a crystal protein toxin that kills the cells lining the insect's gut. When ingested, the bacterial cell wall is digested which then releases the toxins. As young insects have guts that are only one cell layer thick, this toxin literally eats a hole in the insect's gut casing an infection in the body cavity. The exposed insect is either killed or disabled within an hour or a few days.
BT must be eaten by the insect to be active. BT is applied by aerial spray, spraying from a truck, a backpack or hand held sprayer. Use rates are from 0.004 to 0.08 pounds of active ingredients per acre, usually about 2 quarts per acre, from aerial spraying.
Application should start after leaves are open and as soon as most larvae have hatched and have begun feeding.
In the Gypsy Moth Suppression Program in Washtenaw County, Mich. (Ann Arbor area) the use of BT reduced infestation by 70% to 80% in those areas that were sprayed.
Due to its widespread use and the development of fermentative technology the BT bacterium can be grown in artificial media and gallons can be produced economically.
Relatively inexpensive depending on method of application.
Pros and Cons:
1. Harmless butterflies and moths are also at risk from ingestions.
2. Timing of application is critical. Only the young caterpillars have guts thin enough for the BT to punch holes in it. For the Gypsy Moth, once the larvae have gotten larger than 5/8", they become difficult to kill with BT. BT must be applied after the eggs have hatched but before the caterpillar have reached the third instar.
1. BT is a naturally occurring, soil dwelling bacterium.
2. BT and its toxins are killed within three to five days by sun fight and other microbes although spores of BT may remain in the soil for a few days to weeks.
3. BT is not active in the soil and is not absorbed from the soil by plants.
4. The EPA concludes that BT is not a risk to groundwater.
5. The active ingredients in BT do not evaporate into the air.
6. BT is harmless to mammals.
Human Health Risks:
There is no report of effects of BT for human exposure by either inhalation or intravenous routes. Administration of BT Berliner to humans in 1959 experiments did not cause any detectable disease, clinical symptoms or any pathological processes. There are no reported long-term health effects in humans from BT or its formulation. No impact to health would result from contacting or consuming vegetation, water or animals exposed to BTs.
Bacillus Thurinyiensis Pesticides Fact Sheet Prepared for the US Department of Agriculture, Forest Service by Information Ventures, Inc. 1995
Controlling the Gypsy Moth with BT (Bacillus Thuringiensis)-Extension Fact Sheet The Ohio State University Extension HYG-2174-99 1999
Suppressing Gypsy Moths in Washtenaw County Washtenaw County Extension MI 1998.