# Bti

> Bacillus thuringiensis subsp. israelensis, a bacterial strain whose toxins kill fly larvae, including fungus gnats, after ingestion; applied as a medium drench.

- Canonical: https://genetixbay.com/knowledge/glossary/bti.html
- Also written: Bacillus thuringiensis israelensis, B.t.i., Bt israelensis, Bt for fungus gnats
- Glossary category: Pests and diseases · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

Bti is *[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md)* subspecies *israelensis*, a strain whose crystal toxins are active against the larvae of certain flies: mosquitoes, black flies and [fungus gnats](https://genetixbay.com/knowledge/glossary/fungus-gnat.md). Larvae must eat the bacterium for it to work. It has no effect on adult flies, caterpillars, beetles, [mites](https://genetixbay.com/knowledge/glossary/two-spotted-spider-mite.md) or plants.

## In practice

Growers drench the medium with a Bti solution, or soak granules in water and use the liquid, to cut fungus gnat larvae in the top few centimetres of soil or [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md). Results show as fewer adults on [sticky traps](https://genetixbay.com/knowledge/glossary/sticky-trap.md) one to two weeks later, since existing adults are untouched. It breaks down within days, so repeated drenches at roughly weekly intervals during heavy pressure are typical. It pairs well with drying the medium surface and with [nematodes](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md) or [soil predatory mites](https://genetixbay.com/knowledge/glossary/stratiolaelaps-scimitus.md). Check what is registered for cannabis locally.

## Don't confuse with

- **Btk**: the caterpillar strain, sprayed on foliage.
- **Steinernema feltiae**: living nematodes, not a bacterial toxin.
- **Hydrogen peroxide drenches**: oxidisers that also harm beneficial root life.

## Related terms

[Bacillus thuringiensis](https://genetixbay.com/knowledge/glossary/bacillus-thuringiensis.md), [Fungus gnat](https://genetixbay.com/knowledge/glossary/fungus-gnat.md), [Steinernema feltiae](https://genetixbay.com/knowledge/glossary/steinernema-feltiae.md), [Biological control](https://genetixbay.com/knowledge/glossary/biological-control.md)

## Read more

- [Fungus gnats: the watering problem with wings](https://genetixbay.com/knowledge/pests/fungus-gnats.md)

## Sources

1. UC IPM. Pest Notes: Fungus Gnats (Publication 7448). https://ipm.ucanr.edu/legacy_assets/pdf/pestnotes/pnfungusgnats.pdf
2. UConn IPM. Biological Control of Fungus Gnats. https://ipm.cahnr.uconn.edu/ipm-biological-control-of-fungus-gnats/