Bacillus thuringiensis
What's Bacillus thuringiensis (Bt)
Bacillus thuringiensis (Bt) is a kind of beneficial microorganism that exists widely in nature. It produces proteins that are toxic to immature insects (larvae). There are many types of Bt bioinsecticide. Each target targets a different group of insects. Target insects include beetles, mosquitoes, root aphids, nematodes, caterpillars, and grub.
Currently, there are more than 180 registered bacillus thuringiensis products on the market. Bt insecticide products are used in crops and ornamental plants. These products are usually aerosols, dust, particles. Some of these products have been approved for organic agriculture.
Bacillus thuringiensis characteristics
The colony of Bacillus thuringiensis on the NA medium is round or oval, light yellow, with irregular edges, opaque, and slightly raised, and waxy.
Bacillus thuringiensis cells are purple elliptical rod-shaped under the microscope, with a size of (1.2～1.8)μm×(3.0～5.0)μm, arranged in short or long chains. The spores are elliptical and grow near the middle. How does Bacillus thuringiensis (Bt) work
Bacillus thuringiensis produces a protein that is toxic to immature insects (larvae) called parasporal crystals. Target insects beetles, mosquitoes, root aphids, nematodes, caterpillars, and grub.
When these insect larvae gnaw on the leaves with the bacteria, the parasporal crystals will be dissolved and released in the insect’s highly alkaline intestines, preventing the larvae from further eating plants, loss of appetite, endotoxins destroying the intestinal cell wall, and finally breaking the intestine, leading the toxins to enter the larvals’ blood system, causing systemic poisoning. Infected insects stop foraging within a few hours and die within a few hours to a few weeks (usually 2-3 days).
This mechanism can make Bt harmless to fish and mammals because their acidic intestinal conditions inhibit bacterial toxin dissolution.
Due to its non-chemical pollution and low toxicity, Bacillus thuringiensis has been widely recognized and used since the 1950s, and is often used as a biological pesticide, biocontrol agent in organic agriculture.
Application in Agriculture
As a biopesticide, Bacillus thuringiensis (Bt) has many advantages compared with chemical pesticides.
- It is non-toxic to mammals and safe to use. Since the intestinal environment of mammals is acidic, parasporal crystals have no effect in the intestines of these animals.
- It has strong selectivity and specificity and does not harm other beneficial insects. Bt bacteria only specifically infect Lepidoptera insects.
- Strong sustainability. Bacillus thuringiensis is a microorganism that can multiply in nature without destroying the soil structure.
- Naturally, control pest density.
- The control of pests helps prevent the widespread of plant pathogens or viruses.
Because it is a microbial agent, it has high environmental requirements and is toxic to animals such as silkworms, so its use has certain limitations. But this natural insecticidal mechanism meets the environmental requirements of organic agriculture.
Reference: *Bacillus Thuringiensis Application，
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