Fungus gnats are pest insects of the size of fruit flies that mainly harm indoor houseplants. Adult gnats are attracted to the moisture in potting soil and lay their eggs on organic debris matter near the soil surface.
Adult fungus gnats are delicate, grayish-black, mosquito-like flies (1/8 inch long) with long legs and one pair of clear wings. They are not strong fliers and emerge from potted plants, especially when watering.
Adults live about one week and lay up to 300 eggs in the cracks and crevices of growing media such as rich, moist soils. They develop in four stages, namely egg, larva including four larval stages or instars, pupa, and adult.
Plant symptoms that indicate fungal gnats are seen as sudden wilting, loss of vigor, poor growth, and yellowing. With severe infestations, a considerable portion of the plants may be lost. Especially prone to injury:
1. Inspect plants thoroughly prior to purchase for signs of insect pests. Turn up soil carefully near the base of the plant and look for the glossy, clear larvae. Reject any plant sending up flying gnats.