Bacillus Thuringiensis (Bt)

Bacillus thuringiensis is a live microorganism that kills certain insects and is used to kill unwanted insects in forests, agriculture, and urban areas.

Bacillus thuringiensis  (Bt)  is a natural occurring, soil-borne bacteria that has been used for natural insect control. It consists of 1) a spore, which gives it persistence, and 2) a protein crystal within the spore, which is toxic. That toxic protein differs, depending on the subspecies of Bt producing it, yielding a variance of Bt toxic to different insect species (or none at all). When the bacteria is consumed by certain insects, the toxic crystal is released in the insects highly alkaline gut, blocking the system which protects the pest’s stomach from its own digestive juices. The stomach is penetrated, and the insect dies by poisoning from the stomach contents and the spores themselves. This same mechanism is what makes Bacillus thuringiensis harmless to birds, fish and mammals whose acidic gut conditions negate the bacteria’s affect.

Bacillus thuringiensis products are used to control moth pests in fruits, vegetables, and beehives; blackfly and mosquito pests in ponds and lakes; and several beetle pests in vegetables and shade trees.

In China, the most common commercially available subspecies (also called serotypes or varieties) often read as:

  1. Bacillus thuringiensis var kurstaki
  2. Bacillus thuringiensis var aizawai Bonnefoi et de Barjac
  3. Bacillus thuringiensis var israelensis

Formulation are including

i) TC (Technical Concentrate) as per standard GB/T19567.1-2004;
ii) SC ( Suspension Concentrate) as per Standar GB/T19567.2-2004 ;
iii ) WP ( Wettable Powder) as per Standard GB/T19567.3-2004.

A general undertanding about specificaiton for the techincal concentrate is listed as below:
Items Specification
Bacillus thuringiensis var aizawai Bonnefoi et de Barjac Bacillus thuringiensis var kurstaki de Barjac and Lemill
Grade A Grade B Grade A Grade B
Toxin albumen , (130kDa)/(%), 8.0 min. 7.0 min. 7.0 min. 6.0 min.
i) Virulence potency, Ha IU/mg (p.x., h.a)/(IU/mg)     50000 min. 40000 min.
ii) Virulence potency, Ha IU/mg (s.e., h.a)/(IU/mg) 60000 min. 50000 min.    
pH Range 5.5~7.0
Water, % 6.0 Max.
Fineness (75 μ m) 98% min.

Note: i) Virulence potency, Ha IU/mg (p.x., h.a)/(IU/mg) is based on plutella xylostella, and heliothis armigera ; ii) Virulence potency, Ha IU/mg (s.e., h.a)/(IU/mg) is based on Spodoptera exigua

Mode of action:
Mode of Action When conditions for bacterial growth are not optimal Bacillus Thuringiensis, like many bacteria, forms spores. Spores are the dormant stage of the bacterial life cycle, when the organism waits for better growing conditions. Unlike many other bacteria, when Bacillus Thuringiensis creates spores it also creates a protein crystal. This crystal is the toxic component of Bacillus Thuringiensis . After the insect ingests Bacillus Thuringiensis, the crystal is dissolved in the insect's alkaline gut. Then the insect's digestive enzymes break down the crystal structure and activate Bacillus Thuringiensis's insecticidal component, called the delta-endotoxin. The delta-endotoxin binds to the cells lining the midgut membrane and creates pores in the membrane, upsetting the gut's ion balance. The insect soon stops feeding and starves to death. If the insect is not susceptible to the direct action of the delta-endotoxin, death occurs after Bt starts vegetative growth inside the insect's gut. The spore germinates after the gut membrane is broken; it then reproduces and makes more spores. This body-wide infection eventually kills the insect.

Comparing with conventional pesticides which are synthetic material, Bacillus thuringiensis is less toxic to mammals and shows fewer environmental effects. and it is leading furture of agrocultrue pesticides in a nature way.