🐛 Bacterial Biopesticides
Bacterial Biopesticides — Bacillus thuringiensis (Bt), Cry proteins, strains, formulations, and Bacillus subtilis in crop protection.
This lesson builds core elective concepts in BSc Agriculture with practical applications and exam-oriented clarity.
Bacterial Biopesticides
Bacteria are the most commercially successful group of microbial biopesticides. Bacillus thuringiensis (Bt) alone accounts for over 70% of the global biopesticide market, making it the single most important biocontrol agent in agriculture.
Bacillus thuringiensis (Bt)
Bt is a gram-positive, spore-forming soil bacterium that produces insecticidal crystal proteins (Cry proteins or delta-endotoxins) during sporulation. These proteins are toxic to specific insect orders upon ingestion.
Mechanism of Action
- Insect larva ingests Bt spores and crystal proteins
- Crystal proteins dissolve in the alkaline gut (pH 9-11) of the insect
- Protoxins are activated by gut proteases into active toxins
- Toxins bind to specific receptors on midgut epithelial cells
- Pore formation leads to cell lysis, gut paralysis, septicaemia, and death within 24-72 hours
Important Bt Strains and Target Pests
| Subspecies | Cry Protein | Target Insects |
|---|---|---|
| Bt kurstaki (Btk) | Cry1Aa, Cry1Ab, Cry1Ac | Lepidoptera (bollworms, diamondback moth) |
| Bt israelensis (Bti) | Cry4, Cry11 | Diptera (mosquitoes, blackflies) |
| Bt tenebrionis | Cry3A | Coleoptera (Colorado potato beetle) |
| Bt aizawai | Cry1C | Lepidoptera (Spodoptera, wax moth) |
Commercial Formulations
Bt products are available as wettable powders (WP), suspension concentrates (SC), and water-dispersible granules (WG). In India, popular Bt formulations include Dipel, Halt, Biolep, and Delfin. The recommended application rate typically ranges from 1-2 kg/ha depending on formulation and pest pressure.
Bacillus subtilis
Bacillus subtilis is used primarily as a biofungicide rather than an insecticide. It suppresses plant pathogens through:
- Production of lipopeptide antibiotics (iturin, surfactin, fengycin)
- Competition for nutrients and colonization sites on plant surfaces
- Induced systemic resistance (ISR) in host plants
Commercial products include Serenade and Companion, effective against diseases such as powdery mildew, Botrytis, Rhizoctonia, and Fusarium.
Other Bacterial Agents
- Bacillus sphaericus — effective against mosquito larvae in polluted water
- Pseudomonas fluorescens — biocontrol of soil-borne pathogens through siderophore production and antibiosis
- Serratia marcescens — suppresses fungal pathogens via chitinase production
Bacterial biopesticides remain the cornerstone of biological crop protection due to their proven efficacy, safety, and ease of mass production.
Summary Cheat Sheet
| Topic | Key takeaway |
|---|---|
| Main focus | Bacterial Biopesticides — Bacillus thuringiensis (Bt), Cry proteins, strains, formulations, and Bacillus subtilis in crop protection. |
| Section context | Revise this lesson with the rest of Biopesticides and Biofertilizers for stronger conceptual continuity. |
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