Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
7/24/03
FOR IMMEDIATE RELEASE
Contacts:
Linda Naeve, Reiman Gardens, (515) 294-8946, lnaeve@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
"Bt" for Safe, Biological Pest Control in the Garden
By Linda Naeve
Extension Coordinator
Reiman Gardens
Mother Nature has provided her own form of pest control long before humans knew what pests were. Her form of pest control is referred to as "biological control." It involves the use of one organism to suppress another. The organism may be a predator, parasite or pathogen that attacks a harmful insect, weed or disease. This week's Reiman's Pick is a bacterial disease of insects, Bacillus thuringiensis, "Bt" for short.
Several strains of Bt have been identified that infect and kill insects. Because of this property, Bt has been developed commercially for the control of specific pests. It is used mainly to control larvae (caterpillars) of insects in the Lepidoptera order (butterflies and moths) and for the control of mosquito larvae.
Bt is a naturally occurring bacterium common in soils throughout the world. The insecticidal activity of Bt was first discovered in 1911; however, a product containing this bacterium as the active ingredient was not commercially manufactured until the 1950s. Commercial Bt products are powders containing a mixture of dried spores and toxin crystals. They are applied to leaves where caterpillars feed.
Bt is very effective in the control of many caterpillars that feed on garden crops and landscape trees, such as cabbageworms, tomato hornworms, tent caterpillars and fall webworms. Besides being an extremely effective control measure, it is considered safe to humans and non-target species, such as pets, lady beetles, dragonflies, frogs and other wildlife. It also can be used right up until harvest, allowing for timely harvest and long-term control. Best of all, Bt is not known to cause injury to plants and is not considered harmful to the environment.
Since Bt is a living organism, it is handled and applied a bit differently than other insecticides. It controls only the larval stage of butterflies and moths, so timing its use is important. Bt should be applied to the underside of the leaves because most larvae feed on the underside of leaves and Bt breaks down faster in sunlight, which will reduce its effectiveness. When using Bt, mix up only the amount that you will use because the organism may be effective for only one to three days. Like other foliar-applied insecticides, rain or overhead irrigation can reduce the effectiveness by washing Bt from the leaves.
Bt kills the caterpillars in a rather interesting way. First, the Bt spores must be eaten by the young caterpillar. Then the bacteria grows inside the caterpillar, reproduces and produces crystalline toxins. The toxins paralyze the digestive tract of the caterpillar, causing it to stop eating. The caterpillar soon dies of starvation and/or tissue damage. This will take anywhere from 12 hours to five days, depending upon how much Bt the caterpillar ate, the size and species of the caterpillar, and the type of Bt used.
There are several products containing Bt registered for use in Iowa, such as Dipel, Thuricide, Caterpillar Killer and Biobit HB Biological Insecticide.
It seems a bit strange to discuss killing caterpillars when nearly 800 butterflies are introduced each week and enjoyed by thousands of visitors to Reiman Gardens. Unfortunately, no matter how beautiful the adults are, the caterpillars need to eat and as a result some can cause serious damage to crops and landscape plants.
-30-
|
Editors: A color photo, suitable for publication, is available at right. Click on the thumbnail photo to go to the fullsized photo. The picture's fullsize photo is 300K. Caption: Bacillus thuringiensis (Bt) is a natural, safe, and selective control for specific insect pests, like this cabbage looper caterpillar. |
 |
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.