BTI for Pest Control: A Complete Guide for Mosquitoes and Fungus Gnats

If you're looking for a safe, effective, and natural way to control two of the most annoying pests—mosquitoes and fungus gnats—you've likely heard of BTI. This powerful biological agent is a game-changer for gardeners and homeowners. While it targets both pests, the way you use it differs significantly.

This guide breaks down everything you need to know about using BTI against mosquitoes and fungus gnats, helping you choose the right strategy for your problem.

What is BTI?

Bacillus thuringiensis subsp. israelensis (BTI) is a naturally occurring soil bacterium used as a biological larvicide. It produces protein crystals that are toxic only to the larvae of specific insects, including mosquitoes, black flies, and fungus gnats.

When mosquito or gnat larvae ingest BTI, the proteins disrupt their gut function, causing them to stop feeding and die within 24-48 hours. Crucially, BTI is non-toxic to humans, pets, birds, fish, bees, and earthworms when used as directed, making it an environmentally friendly cornerstone of Integrated Pest Management (IPM).

BTI vs. Mosquitoes: Outdoor Water Treatment

For mosquitoes, BTI is a preventative treatment applied to the standing water where they breed.

• Primary Method: Products like Mosquito Dunks (donut-shaped) or Mosquito Bits (granular) are placed in or sprinkled over any non-potable standing water.

• Key Habitats: This includes bird baths, rain barrels, clogged gutters, plant saucers, ponds, and unused pools.

• Mechanism: The BTI gradually disperses in the water. Female mosquitoes lay eggs, the eggs hatch into larvae (wrigglers), the larvae ingest the BTI while filter-feeding, and they die before becoming flying adults.

• Strategy: It is a long-term, population control strategy. By consistently treating breeding sites, you break the life cycle and reduce the number of new adult mosquitoes over time.

BTI vs. Fungus Gnats: Indoor Soil Drench

For fungus gnats, which infest the moist potting soil of houseplants, the application of BTI is fundamentally different.

• Primary Method: The most effective technique is to create a "BTI Tea" or soil drench. You soak Mosquito Bits or a portion of a Mosquito Dunk in water for 30 minutes to several hours, then use the strained liquid to thoroughly water your plants.

• Key Target: The treatment is applied directly to the soil, where fungus gnat larvae live and feed on organic matter and fungi.

• Mechanism: The BTI in the water is absorbed by the soil. When the tiny, soil-dwelling gnat larvae ingest it, it fatally damages their gut lining.

• Strategy: This is a curative treatment for an active infestation. It must be repeated to break the breeding cycle, as new adults can emerge or be introduced.

Direct Comparison: Application & Strategy

Pro Tips for Effective Use

• For Mosquitoes: Eliminate the water first. Before using BTI, tip over any containers holding water. Use BTI for water that cannot be drained, like ponds or rain barrels. Consistency is key—reapply as directed.

• For Fungus Gnats: Let soil dry. Fungus gnats thrive in moist soil. Allow the top 1-2 inches of soil to dry completely between waterings. Combine BTI drenches with yellow sticky traps to capture adult gnats. This dual attack on larvae and adults is the fastest way to gain control.

• Storage: Keep unused BTI products in a cool, dry place, sealed in their original packaging to maintain potency.