Moth and Shore Flies

• Moth flies are around 1/10th of an inch long. They have hairy, dark-gray bodies and light-gray, oval-shaped wings. The females lay their eggs in decomposing organic matter during the spring and summer months. Their larvae are approximately 1/4-inch long, with flattened, legless bodies. Shore flies are slightly smaller than moth flies; their dark wings have five lighter-colored spots. Shore fly larvae have brownish-yellow bodies, indistinct heads and a forked breathing tube at the tail. The larvae of both species mature into adults in approximately two weeks.
  
  

Fungus Gnats, March Flies and Whiteflies

• Fungus gnats range in size from 1/16th- to 1/8th-inch long, with light-gray wings and long antennae. Their larvae have clear or white bodies and black heads. March flies vary in color from orange to brown or black depending on the species, and are usually around 3/8ths of an inch long. They produce yellowish or dark-brown larvae with dark-brown heads. Whiteflies are tiny insects with white wings and powdery-white or yellowish bodies. Juvenile whiteflies, or nymphs, are immobile and spend their nymphal stages feeding in one spot.
  
  

Effects

• Moth flies, shore flies, fungus gnats and March flies are more of an irritation than a serious problem, according to the University of California Statewide Integrated Pest Management Program. Shore flies leave excrement on foliage, while fungus gnat larvae feed on plant roots. Adults and larval fungus gnats may also spread pathogens between plants. Whiteflies drain sap from the foliage, causing yellowing and leaf distortion. They also excrete large amounts of a sugary liquid called honeydew, which acts as a growing medium for the sooty mold fungus.
  
  

Control

• You can monitor fly infestations by placing yellow sticky traps in the greenhouse. Predatory insects such as ground beetles and rove beetles provide biological control of most greenhouse flies and gnats; parasitic wasps such as Eretmocerus and Encarsia formosa feed on whiteflies. Bacillus thuringiensis, a bactericide, sickens and kills fly larvae. Some nematode species and predatory mites also feed on larval insects. Since many species breed around standing water, avoid overwatering plants, and check for leaks in irrigation systems.