Bacillus thuringiensis (Bt)
Quick Facts
- Type
- Microbial
- Source
- Naturally occurring soil bacterium producing insecticidal crystal proteins
- OMRI Listed
- Yes ✓
- Bee Safe
- Yes
- Pet Safe
- Yes
- Residual
- 5-7 days on leaf surface; degrades rapidly in UV light
- Best For
- Caterpillar control on vegetables, fruit trees, and ornamentals. Mosquito larvae in standing water (Bti).
What Is Bacillus thuringiensis (Bt)?
Produces Cry proteins that bind to receptors in the insect gut lining, creating pores that cause gut paralysis and death within 24-72 hours. Only activates in alkaline gut pH (caterpillars, mosquito larvae), so it is highly selective.
Source: Naturally occurring soil bacterium producing insecticidal crystal proteins
What Pests Does Bacillus thuringiensis (Bt) Kill?
Bacillus thuringiensis (Bt) is effective against the following pests:
How to Apply Bacillus thuringiensis (Bt)
Best for: Caterpillar control on vegetables, fruit trees, and ornamentals. Mosquito larvae in standing water (Bti).
Avoid for: Beetles (except Bt galleriae), aphids, mites, or any sucking insect — Bt only works through ingestion.
Residual activity: 5-7 days on leaf surface; degrades rapidly in UV light
Safety Profile
| Category | Rating |
|---|---|
| Bee Safety | 🟢 Safe for bees |
| Pet Safety | 🟢 Safe for pets |
| Overall Rating | Safe — Safe for kids, pets, and bees when used as directed |
Why Isn't Bacillus thuringiensis (Bt) Working?
If Bacillus thuringiensis (Bt) isn't delivering results, check these common failure modes:
Applied too late — caterpillars must ingest treated foliage while still feeding actively
Wrong subspecies — Btk for caterpillars, Bti for mosquitoes/fungus gnats, Bt galleriae for beetles
UV degradation — reapply after rain or every 5-7 days
Resistance buildup in monoculture crops without rotation
Best Bacillus thuringiensis (Bt) Products
Monterey B.t.
ConcentrateBtk strain — the caterpillar standard
Summit Mosquito Bits
GranulesBti strain for fungus gnats and mosquito larvae
BeetleGONE!
SprayBt galleriae strain for Japanese beetles and grubs