BIOLOGICAL CONTROL OF FUNGUS GNATS
Predatory mites, Stratiolaelaps scimitus (formerly Hypoaspis miles), are currently employed for the biological control of fungus gnats (Bradysia spp.).
FUNGUS GNATS
Fungus gnats, Bradysia spp., are small insects measuring approximately 0.125 inches in length, with brownish to blackish coloring and a single pair of clear wings (Photo 1). The larvae of fungus gnats are white, transparent, have shiny black heads, and are about 0.25 inches long (Photo 2).
Photo 1. Fungus gnat adult
Photo 2: Larvae of Fungus Gnats
DAMAGE CAUSED BY FUNGUS GNATS
The life cycle of fungus gnats consists of four stages: adults, eggs, larvae, and pupae. Only the larval stages can directly damage plants, especially those grown in enclosed structures like greenhouses and homes. Although adult fungus gnats are not directly harmful to plants, they can indirectly damage them by spreading spores of plant diseases.
DIRECT DAMAGE BY FUNGUS GNAT LARVAE
Fungus gnat larvae cause direct feeding damage by chewing, stripping, and tunneling through the roots and stems of host plants. Heavily infested plants often appear sick, discolored, and may die prematurely.
INDIRECT DAMAGE BY FUNGUS GNAT LARVAE
While feeding on roots and stems, larvae transmit disease-causing fungal pathogens like Fusarium, Phoma, Pythium, and Verticillium to host plants. These pathogens cause various diseases and ultimately lead to the death of infected plants.
INDIRECT DAMAGE CAUSED BY FUNGUS GNAT ADULTS
Adult fungus gnats are harmless to plants but can be a nuisance to people. Additionally, these adults spread spores of many disease-causing fungal pathogens from plant to plant as they migrate through homes or greenhouses.
PREDATORY MITE, STRATIOLAELAPS SCIMITUS
Stratiolaelaps scimitus are predatory mites (Photo 2) currently used as biological control agents against fungus gnats, which are economically significant insect pests of potted plants in homes and greenhouses. Adults are brown to tan and approximately 0.8-1.0 mm in size. They lay oval-shaped and colorless eggs. Stratiolaelaps scimitus larvae are brown to black in color with six legs whereas their nymphs resemble their parents. These mites complete their egg-to-egg life cycle at temperatures between 15-25°C (59-77°F) within 15 days.
Phot 3. Stratiolaelaps scimitus mite
HOW DO STRATIOLAELAPS SCIMITUS MITES CONTROL FUNGUS GNATS?
When both the adult and nymphal stages of Stratiolaelaps scimitus mites are released in pots with fungus gnat-infested plants, they locate and feed on eggs, larvae, and pupae, reducing the fungus gnat population. These mites do not feed on adult fungus gnats.
WHEN AND HOW STRATIOLAELAPS SCIMITUS MITES SHOULD BE RELEASED?
Release Stratiolaelaps scimitus mites immediately upon arrival. If a delay is unavoidable, store them at 10-20°C (50-60°F) for a few days. Ensure bottles are stored on their side with filter paper up to prevent overcrowding. Release mites on potting media, soil, dirt, gravel floors, weeds, and groundcovers near fungus gnat reproducing areas. Rotate the bottle to mix mites evenly, open the bottle, remove filter paper, and tap mites onto fungus gnat-infested surfaces.
HOW MANY STRATIOLAELAPS SCIMITUS MITES SHOULD BE RELEASED?
For effective control:
Release 5-10 mites/square foot bi-weekly, 2-3 times.
Release 25,000 to 50,000 mites/acre bi-weekly, 2-3 times.