Fungus gnats are also known as sciarid flies. The larvae feeds on small roots, causing a lot of damage, especially in propagation nurseries and in potted plants.
The larvae do not only feed on decaying organic material such as algae and mold, but also on living material such as root and stalk tissue. They pierce into the root and/or stalk of cuttings, seedlings or young plants. As a result of this, secondary plant diseases such as Pythium, Phytophtora, Botrytis, Fusarium and Verticillium can be spread. The general symptoms of such an attack are the wilting and the slowing down of the growth of the plants. In the worst case, this might even lead to death of these plants.
Adults of fungus gnats are 3-5 mm long dark flies with long, slender antennae and long legs. They are particularly seen in a warm and humid environment in the proximity of plants. That's why they can occur the whole year round in greenhouses. After mating, the female fly lays 50-200 eggs, which hatch in 2-3 days. The emerging larvae develop through four instars over 2-3 weeks. By that time, they are about 5 mm long, translucent white in colour with a distinctive black head. They pupate in the compost and emerge as adult flies 3 days later. At temperatures in excess of 24°C, breeding is continuous and the life cycle takes 3-4 weeks.