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DARKWINGED FUNGUS GNATS

James R. Baker, Extension Entomologist, Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

[General Information] [Biology] [Control] [Other Resources

General Information

Lycoriella spp. and Bradysia spp., Sciaridae, DIPTERA

line drawing of adult maggot and pupa small photo of fungus gnat adultDarkwinged fungus gnats are slender with comparatively long legs and antennae. They are grayish-black and about 1/8 inch long. The eggs are yellowish-white and tiny. Darkwinged fungus gnat maggots have shiny black head capsules and white bodies. The last body segment is lobed and helps push the insect along. Mature larvae are about 1/4 inch long. Initially white, pupae become dark shortly before the adult emerges.

Biology

Darkwinged fungus gnat maggots feed on the roots of alfalfa, carnations, clover, corn, cucumbers, Easter lilies, geraniums, lettuce, nasturtium, peppers, poinsettias, potatoes, soybeans, wheat, and organic matter throughout the United States. Damage first becomes apparent when plants lose their healthy appearance and wilt. Darkwinged fungus gnat adults are usually noticed before injury caused by the maggots is apparent.

Darkwinged fungus gnat maggots are important pests in some greenhouses and mushroom cellars. Besides the adult nuisance factor, heavy larval populations can damage roots and enter tender stems at soil level. They are also pests of house plants. Several of these flies are of economic concern. In greenhouses, darkwinged fungus gnats are generally most abundant in the winter and spring. Adults and larvae inhabit moist, shady areas. Adults live about 1 week, during which time each female deposits 100 to 150 eggs. They are laid in strings of 3 to 40 on soil, usually near stems of plants. They hatch within 4 days in the greenhouse. There is a tendency for the progeny of each female to be all one gender.

The larvae begin feeding on the root hairs and roots usually in the upper two inches of medium, working their way up the plant and into the stem. However, they also feed on any organic matter in the soil. Being somewhat gregarious, the larvae often form clusters in the soil. They mature in about 14 days, after which they construct a pupal case in the soil made of silk and debris. The pupal stage lasts about 3.5 days. Adults are weak fliers, but they run rapidly on the soil surface or may remain motionless to avoid predation.

maggots slitherin togetherIn turf, they are occasionally seen in high numbers.  This is usually in high organic soils and areas of heavy thatch following wet periods.  Adjacent natural areas and mulched beds may contribute to the situation.  If a large number of eggs hatch near each other and the maggots migrate, they may form a snake-like line crawling atop each other.  These are most often noticed when moving across a sidewalk or driveway.  Though these are rarely of any consequence in the landscape, some homeowners desire control.  A pyrethroid lawn and garden spray (permethrin, bifenthrin) is adequate.  For information about fungus gnat adults indoors, see residential/urban note #29.

Control

In homes, darkwinged fungus gnat problems can be greatly reduced by allowing the soil of houseplants to dry out occasionally between waterings. In the landscape, make sure mulch layers are not too thick (<3") and automatic watering systems are not set disregarding soil moisture conditions.

In greenhouse or nursery settings, clean cultural practices and lack of excessive watering usually will prevent fungus gnat infestations. Repair leaky watering systems and do not allow algal buildup anywhere and not just on the benches. Since fungus gnats prefer potting mixes containing peat moss and abundant moisture, consider using bark mixes and avoid overwatering ornamental plants. Some studies have shown that fungus gnats are often introduced in the peat moss and plant plugs. Investigate your current brand.  Decoy pots of sprouting grain are attractive to females that lay eggs in these pots. Afterwards, the pots should be submerged in boiling water or the contents destroyed in some manner every 2 weeks to destroy the eggs and maggots.  Sticky card traps and fresh potato slices can be used as monitoring tools when used correctly.

Fungus gnats have few efficient natural enemies. The predaceous nematode, Steinernema bibionis, has reduced fungus gnats in mushroom houses 85 percent. Another nematode, Steinernema carpocapsae, is now on the market for fungus gnat control in greenhouses. A small, soil-dwelling predatory mite, Hypoaspis miles, feeds on fungus gnat larvae and is commercially available and compatible with nematodes and Bacillus thuringiensis var. israelensis. Some species of fungus gnats in mushroom houses have developed up to 47-fold resistance to pyrethroid insecticides.
 

Pesticide  (Trade Name)  Formulation 
diflubenzuron (Adept) check label for phytotoxicities
bifenthrin  (Talstar)  10% wettable powder 
cyfluthrin  (Decathlon)  20% wettable powder 
kinoprene  (Enstar II)  65.1% emulsifiable concentrate 
nematodes, predaceous 
Steinernema feltiae (Nemasys or Scanmask)
17% aquaeous solution 
pyriproxyfen (Distance) check label for phytotoxicities
See NC Pesticide Manual for additonal choices.    

Helpful links:

Kansas State Fungus Gnat IPM
UConn Bio Control Note 
UConn Pest Note
University of Illinois Note
Insects Found on Yellow Sticky Cards in the Greenhouse
U.C.Davis Note
TAMU Insect Profile

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

© 2001 NC Cooperative Extension Service


Prepared by: James R. Baker & S. B. Bambara, Extension Entomologists
ENT/ort-29
May 1994 (Revised) May 1997. Lightly revised January, 2004.

Web page last reviewed January, 2011 by the webperson.