Microorganisms as Biological Control Agents of Mushroom Flies
The use of BTI (Bacillus thuringiensis var. israelensis) in
button mushroom (Agaricus bisporus) cultivation is a highly effective and
targeted biological control method. It is specifically used to combat one of
the most persistent and damaging pests in mushroom farming: fungus gnats and
sciarid flies.
They:
- Feed
on Mycelium: They tunnel through the compost, feeding on and damaging
the precious Agaricus mycelium, which directly reduces yield.
- Feed
on Mushroom Pins: They can chew on the developing pinheads,
destroying them before they can grow into marketable mushrooms.
- Spread
Diseases: The larvae and adults can act as vectors, spreading fungal,
bacterial, and viral diseases (like Lecanicillium dry bubble) throughout
the crop as they move from one area to another.
Larvae are the Problem:
The adult flies are harmless to the mushrooms themselves,
but they lay eggs in the compost and casing soil. The hatched larvae are the
destructive stage. The Primary Target: Sciarid Flies and Fungus Gnats.
These small, flying insects are not just a nuisance; they
are a direct threat to the crop.
- · Adult Flies
- · Fungal Diseases
- · Dry Bubble
- · Adult Flies
BTI is applied at several critical points in the
production cycle to break the life cycle of these pests.
1. On the Compost (Phase I, Phase II, and Spawn Run)
- Purpose:
To target larvae that may be present in the compost before it even
goes into the growing rooms. This is a preventative measure.
- Application:
BTI can be mixed into the compost during the wetting-down phase or
applied as a drench after pasteurization (Phase II) and during spawning.
2. On the Casing Soil
- Purpose:
This is the most critical application point. The moist, un-colonized
casing layer is the ideal place for female sciarid flies to lay their
eggs. Applying BTI here ensures that the larvae will ingest it as soon as
they hatch.
- Application:
BTI is thoroughly mixed into the casing soil (e.g., peat lime) before it
is applied to the colonized compost. It can also be applied as a drench
after casing.
3. As a Surface Drench or Spray in the Growing Rooms
Purpose: To control larval populations that hatch
from eggs laid after casing. This is a curative measure.
Application: A BTI solution is sprayed or drenched onto the surface
of the cased beds during the spawn run and cropping period. This is especially
important if adult flies are spotted in the rooms.
4. As Part of the Overall IPM (Integrated Pest
Management) Program
Purpose: BTI is rarely used alone. It is a core
component of an IPM strategy.
Integration:
Physical Barriers: Insect screens on air inlets and
doors to prevent adults from entering.
Traps: Sticky yellow or blue cards are used to
monitor and trap adult flies. This helps gauge the severity of the infestation
and the effectiveness of control measures.
Sanitation: Prompt removal of spent compost (husk)
and thorough cleaning between crops are essential to eliminate breeding sites.
Other Controls: In severe cases, selective
insecticides might be used against adults, but BTI remains the primary weapon
against the larvae.
Why BTI is Ideal for Mushroom
Cultivation
Highly Specific: BTI produces protein crystals that
are toxic only upon ingestion by the larvae of specific Diptera (flies),
including sciarids and fungus gnats. It is completely harmless to: The mushroom
mycelium and fruit bodies.
Humans, pets, and other non-target insects.
Beneficial organisms that might be used, like predatory
mites (Hypoaspis miles).
Biological and Organic: It is a naturally occurring
bacterium, making it suitable for organic certification and reducing the reliance
on synthetic chemical pesticides.
No Residue Issues: Since it is a biological agent,
there is no risk of chemical residue on the harvested mushrooms, which is a
critical food safety concern.
Resistance Management: Using a biological agent with
a specific mode of action helps slow the development of pesticide resistance in
pest populations.
Why BTI is Ideal for Mushroom Cultivation
Practical Application Forms
In a commercial mushroom plant, BTI is typically used in
these formulations:
Wettable Powders (WP):
Mixed with water and sprayed or drenched onto beds and
casing.
Liquid Formulations:
Ready-to-mix concentrates for spray applications.
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