Fungus gnats are small, dark, short-lived flies, of the families Sciaridae, Diadocidiidae, Ditomyiidae, Keroplatidae, Bolitophilidae, and Mycetophilidae (order Diptera); they are sometimes placed in the superfamily Mycetophiloidea.
The larvae of fungus gnats feed on plant roots and fungi, which aids in the decomposition of organic matter. The adults are 2–5 mm long and are important pollinators that can help spread mushroom spores as well as plant pollen.
Typically, overwintering organisms can either avoid freezing or tolerate freezing, but Excechia nugatoria can do both. For E. nugatoria, the production of noncolligative antifreeze proteins (NAPs) protect the head and thorax from freezing, but they do not protect the abdomen.
Freezing of the head and thorax in other insects tends to have adverse effects on neural tissue, so it is not surprising that these protective mechanisms have been observed in certain species, but E. nugatoria is the only insect known to semi-freeze through the winter, which may be an evolutionary advantage according to Sformo: By allowing the abdomen to freeze, evaporative water loss is reduced over the course of the winter.
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Fungus gnats are typically harmless to healthy plants - and humans - but can inflict extensive damage to seedlings; their presence can be indicative of more serious problems. In houseplants, the presence of fungus gnats may indicate overwatering; they may be feeding on roots that have sat in drain water too long and are thus rotting, or the gnats may be attracted to fungus growing in saturated topsoil. Consequently, allowing the soil to dry may reduce their numbers.
Other methods of management may include the following:
- Placing about half an inch of sterile sand on top of the soil around plants; the fungus gnats can't get back to the soil and the larvae can't escape. Indoor mulch may also be effective.
- Introducing Hypoaspis miles mites or applying the biological larvicide Bacillus thuringiensis (subspecies israelensis) to kill the gnats in their larval stage; the larvacide must be applied weekly as a soil drench for 4–5 weeks.
- Annually drenching the soil in an insecticidal soap; neem oil may be used as a repellent when diluted 1 teaspoon per litre of water and applied 300 ml per square meter of soil (4 teaspoons per US-gallon of water, applied 3 avoirdupois ounces per international square foot). Detergents and the nicotine from tobacco brewed into a toxic tea are used by some people to control fungus gnats.
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