Mode of action of BT Bacillus thuringiensis (Bt) produce.pptx

Bacillus thuringiensis (Bt), soil-dwelling bacterium that naturally produces a toxin that is fatal to certain herbivorous insects. The toxin produced by Bacillus thuringiensis (Bt) has been used as an insecticide spray since the 1920s and is commonly used in organic farming.

1. Subject :- Biological control of crop pests and weeds Compiled by :- Dr. Rahul Patidar (Entomology) Class :- M. Sc. (Entomology) Prev. (2 nd Sem.) Department of Entomology College of Agriculture, Indore Rajmata Vijayaraje Scindia Krishi Vishwa Vidyalaya, Gwalior (M.P.)

2. Bacillus thuringiensis (or Bt ) is a facultative anaerobic , gram-positive , soil-dwelling bacterium , commonly used as a biological alternative to a pesticide; alternatively, the Cry toxin may be extracted and used as a pesticide . Bacillus thuringiensis was first discovered in 1901 by Japanese biologist Shigetane Ishiwata , most abundantly found in grain dust from soils and other grain storage facilities. Basic Information of Bacillus thuringiensis

3. One gram of each sample is suspended in 10 ml sterile distilled water and pasteurized at 80°C for 30 min. For the selection of B. thuringiensis , 1 ml of each suspension is added to 10 ml of Luria- Bertani broth buffered with 0.25 M sodium acetate pH 6.8 . The suspensions are incubated at 30°C for 4 h and then heated at 80°C for 3 min . Suspensions were diluted and plated on T3 medium (per liter : 3 g tryptone , 2 g tryptose , 1.5 g yeast extract, 0.05 M sodium phosphate pH 6.8, and 0.005 g of MnCl2 ). After incubation at 30°C for 24 h, the colonies showing similar morphology were selected and examined under phase-contrast microscope to determine the presence of parasporal inclusions and spores. Isolation and Culture of Soil

4. Bacillus thuringiensis is gram-positive . it has a thick cell wall that is comprised of peptidoglycan (amino acid polypeptide and a sugar). Between the cell wall and the plasma membrane is a small section called the periplasmic space which is essential for biosynthesis and protection . Cell structure and metabolism of Bacillus thuringiensis

5. General events of Mode of action:- The first impact of Cry toxins on the insect is cessation of feeding due to paralysis of the gut and mouthparts. In addition to gut paralysis, midgut cells swell leading to an ion imbalance and death. M olecular events of Mode of action:- The molecular events leading to Cry toxin-mediated insect death initial steps are as follows: The Bt Cry and Cyt proteins require solubilization in the insect midgut to produce protoxins that are typically about 130 kDa , 70 kDa or 27 kDa for Cyt . These in turn are proteolytically cleaved at the C-terminus and/or at the N-terminus by midgut proteases, generating the activated core toxin . Mode of Action of Bacillus thuringiensis

6. The toxin then crosses the peritrophic matrix and binds to receptors in the apical membrane of the midgut cells, with specific receptors called cadherins binding being an important determinant of toxin specificity . Toxin insertion into the epithelial membrane forms ion channels or pores, leading to lysis of the cells, damage to the midgut epithelial tissue, and death of the larva Mode of Action of Bacillus thuringiensis

7. Make sure you have the right strain for the pest you want to control. A pH greater than 8 is what activates the toxin in the insect's gut. You will have better control if the larvae are small. There will be less damage to the plants because the little insect s won't eat as much. If you treat larger larvae, they will eat more of the plants and cause greater damage . Also, they may morph into the reproductive phase and become insensitive to the toxin . The spray will be more effective if you add a spreader eader or sticker to the tank mix. Use the spray within 12 hours of mixing. Make sure that you are spraying both the top and bottom surfaces of the leaves. Tips for Applying of Bacillus thuringiensis