Bacillus thuringiensis (Bt)

Introduction

Bacillus thuringiensis (Bt) is a naturally occurring bacterium that produces insecticidal proteins toxic to specific insect groups, especially caterpillars, beetles, and mosquito larvae. It is the world’s most widely used microbial pesticide, offering a residue-free and environmentally safe alternative to chemical insecticides.

Scientific Description

Bt is a gram-positive, aerobic, spore-forming bacterium from the Bacillaceae family. During sporulation, it produces crystalline endotoxins (Cry and Cyt proteins) that, when ingested by larvae, disrupt their gut lining, leading to paralysis and death. These toxins are highly selective, making Bt a precision biocontrol agent.

Benefits

• Highly Targeted Pest Control: Effective against Helicoverpa, Spodoptera, Plutella, Leptinotarsa, and mosquito larvae.
• Safe for Non-Target Organisms: Does not harm pollinators, predators, or humans.
• OMRI-Listed: Approved for organic farming and widely adopted in certified operations.
• No Residue or Resistance Risk: Breaks down in UV light and leaves no harmful residues.
• Compatible With IPM Programs: Can be rotated or combined with Trichoderma, neem, or mechanical controls.

Uses

• Target Pests: Caterpillars (lepidopterans), beetle larvae (coleopterans), and mosquitoes (dipterans).
• Crops: Cotton, cabbage, cauliflower, chili, tomato, brinjal, okra, rice, pulses.
• Application Methods:
  • Foliar Spray: 0.5–1% Bt formulation (typically 1–2 g/L water) with sticking agent
  • Larval Windows: Apply during early larval stages for maximum ingestion
  • Repeat Applications: Every 5–7 days during heavy pest pressure
• Best Conditions: Morning or evening sprays preferred to protect from UV degradation

Trivia

• First discovered in 1901 in Japan and commercialized in the 1950s.
• Basis of many genetically modified Bt crops (e.g., Bt cotton, Bt corn).
• Different Cry proteins target different pests — e.g., Cry1 targets caterpillars, Cry3 targets beetles.
• Still the gold standard for biological insect control in organic farming worldwide.