Damage. The larvae of this pest (sometimes called fungus gnat) feed on fine roots of greenhouse pot plants such as cyclamen, orchid and freesia, causing the plants to wilt. Fungal strands of mushrooms in commercial houses may be attacked in the compost.
Life cycle. The slender black females, which are about 3 mm long, fly to suitable sites (freshly steamed compost, moss on sand benches and well-fertilized compost containing growing plants), where about 100 minute eggs are laid. The emerging legless larvae are translucent-white with a black head, and during the next month grow to a length of 3 mm before briefly pupating and starting the next life cycle.
Control. Amateur gardeners and professional horticulturists use yellow sticky traps to catch the flying adults in greenhouses. The pest can be reduced by avoiding overwatering of plants. Biological control by the tiny nematode Steinernema feltiae is now available. Professional growers in mushroom houses attempt to exclude the flies from mushroom houses by means of fine mesh screens placed next to ventilator fans. A predatory mite (Hypoaspis miles) is used to control the larvae. The larvae also may be controlled by the insecticide, diflubenzuron, incorporated into composts.
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