What is the primary method used to suppress black fly larvae populations in streams?

What is the primary method used to suppress black fly larvae populations in streams?

• A. Bti (Bacillus thuringiensis israelensis) in liquid form poured into moving water
• B. Copper sulfate added to water
• C. Screening streams with mesh to prevent larvae
• D. Introducing large fish to streams

Answer: (A)

A targeted biological larvicide applied directly to streams is the preferred way to suppress black fly larvae. Bacillus thuringiensis israelensis (Bti) is a bacterium that produces toxins lethal to black fly larvae (and some mosquitoes) when the larvae ingest it. In moving water, applying a liquid Bti formulation allows the toxin to disperse through the habitat where larvae are feeding, so contact and ingestion occur in the places where they live on the stream bottom and in riffles. Because Bti is highly specific to these aquatic larvae, it has minimal impact on fish, non-target invertebrates, and other wildlife, making it the safest and most effective choice for stream environments. Copper sulfate, while toxic to some aquatic organisms, is broad-spectrum and can harm non-target species and the overall ecosystem. Screening streams with mesh is impractical in most streams and doesn’t address larval habitats effectively. Introducing large fish can disrupt the ecosystem and doesn’t reliably control black fly larvae across the varied microhabitats in streams.

A targeted biological larvicide applied directly to streams is the preferred way to suppress black fly larvae. Bacillus thuringiensis israelensis (Bti) is a bacterium that produces toxins lethal to black fly larvae (and some mosquitoes) when the larvae ingest it. In moving water, applying a liquid Bti formulation allows the toxin to disperse through the habitat where larvae are feeding, so contact and ingestion occur in the places where they live on the stream bottom and in riffles. Because Bti is highly specific to these aquatic larvae, it has minimal impact on fish, non-target invertebrates, and other wildlife, making it the safest and most effective choice for stream environments.

Copper sulfate, while toxic to some aquatic organisms, is broad-spectrum and can harm non-target species and the overall ecosystem. Screening streams with mesh is impractical in most streams and doesn’t address larval habitats effectively. Introducing large fish can disrupt the ecosystem and doesn’t reliably control black fly larvae across the varied microhabitats in streams.