What is Bt?
You do not have to be a scientist to use Bts effectively or understand how they work.
Bacillus thuringiensis (Bt) is one of the most common microorganisms used in insecticides to control target insects using an environmentally benign, biologically-based agent. Bt is a biological insecticide that:
- Is a rod-shaped microorganism (bacterium) that produces protein toxins during sporulation (spore production process).
- Creates toxins lethal to many pest and disease-carrying insect species, such as caterpillar, beetle, and mosquito larvae.
- Is harmless to humans, birds, and other beneficial wildlife.
- Provides insecticidal properties through commercial Bt products. These commercial Bt products contain protein toxin crystals or a mixture of crystals and Bt spores.
Bts are naturally-occuring throughout most regions of the world, are common in soil and on plant leaves and are biodegradable.
How Do Bts Work?
Bts contain protein endotoxin crystals and living spores. With insect populations, the protein endotoxin acts as a selective stomach poison. Spores contribute to their toxicity by causing blood poisoning and providing environmental persistence.
When an insect pest ingests the crystal proteins from treated leaves, feeding stops within minutes after the crystals are solubilized in the gut and gut cells are damaged. After toxin damage to the gut occurs, spores enter through the gut wall and germinate rapidly in the body cavity causing blood poisoning. Larvae stop feeding within minutes and die in 1-3 days. The affected larvae move slowly, discolor, then shrivel, blacken, and die. Smaller larvae die more quickly, which suggests that precise timing can measurably improve the performance of the application.
Some pest species are difficult to control with toxin alone. Germinating Bt spores provide an additional control mechanism:
- Spores germinate in the midgut and spread throughout, ultimately causing septicaemia (blood poisoning) and death
- Additional mortality (synergistic effect) is especially apparent in armyworm larvae, which can be difficult to control with toxin alone
- Products with viable spores (such as DiPel and XenTari) have a distinct advantage over products without spores
What Types of Bt Exist?
Literally, thousands of Bt strains exist within the various Bt subspecies. Each individual strain produces its own insecticidal protein toxin mix targeting specific groups of pests. There are more than 80 different subspecies of Bt, but commercially, only the following are used:
- Bt kurstaki (Btk) : Used for caterpiller control
- Bt aizawai (Bta) : Used for caterpillar control with specific activity on armyworms
- Bt tenebrionis (Btt) : Used to control beetle larva
- Bt israelensis (Bti) : Used to control mosquito, black fly and fungus gnat
What VBC Agricultural Products are Sold?
High-quality VBC agricultural Bt products are available and sold in more than 100 countries around the world under a variety of names:
DiPel: Btk is sold under the brand name DiPel in addition to being sold as Biobit and Bactospeine. DiPel (Btk) is a broad-spectrum worm/caterpillar product for use on vegetables, fruits, nuts, vines, corn, cotton, soybeans, turf, and other crops. It controls more than 55 caterpillar pests including: leafrollers, bollworms, loopers, hornworms, cutworms, and corn borers. A key benefit of Btk is its status as a nonrestricted use pesticide. It does not require a restricted use permit for either purchase or use, and can be applied up to the time of harvest (although regional regulations vary and should be consulted for allowable preharvest intervals).
XenTari: Bta is sold as XenTari and Florbac. This unique broad-spectrum worm/caterpillar product is particularly effective in controlling armyworms and Diamondback Moth larvae. It is registered for use on vegetables, fruits, nuts, row crops, and turf and is the most effective tool for resistance management.
Understanding the Potency Story
Bt potency is a quality control method that was developed to help a company measure the consistency of the product from one batch to the next. One of the common methods used for quality control methods is the International Units (IU) method established in 1971. Potency was not designed to be used as a method for farmers to determine which product they should use; therefore, it should not be used to determine rates or measure efficacy on insects in the field. Different companies use different methods and insects to measure potency.
It is important to understand that different species have different susceptibilities to Bt toxins. Furthermore, Bt products have different profiles of these toxins. A cabbage looper potency number is useful for quality control only. <<CLICK HERE FOR AUDIO INTERVIEW ON POTENCY>>