Insect UpdateInsect Ecology in Controlled Environments The Ohio State University/OARDC, Wooster canas.4@osu.edu Fungus Gnats(see it in pdf) Currently, the bedding plant season is in full swing and with it we have had more insect activity. Some of the most common problems have involved the presence of fungus gnats. Here I am including a summary of the information we know about fungus gnats. Identification. Fungus gnats are small insects that resemble flies. They belong to the family Sciaridae and one of the most common genera found on ornamentals is Bradisia sp. They only have one pair of wings, have an slender body, with long antenna ( Figure 1 ). Adults can be detected by using sticky traps. However, sticky traps need to be replaced once per week to monitor them effectively. Once caught in sticky traps it is useful to use a hand lens to identify them properly. Main characteristics include clear wings and long antenna. This is relative to another group of insects that can be commonly caught in sticky traps, the shoreflies. Shore flies belong to a different group of insects, the family Ephydridae. Sometimes they can be confused with fungus gnats. However, they have an stocky body, short antenna and some species have characteristic markings in their wings ( Figure 2 ). Of course all these features can only be seen with the aid of a hand lens. Fungus Gnat Cycle and Damage . The life cycle consist of egg, larvae, pupae and adults. The egg to adult cycle can last from two to four weeks. Adult females lay their eggs in moist potting soil. Eggs hatch in 5 to 6 days into white translucent larvae. The larvae takes about 15-25 days to become adults. Larvae have a shiny black head and a whitish legless body. Fungus gnat larvae can feed on roots, which results in plant stunting. Both larvae and adults have been associated with the transmission of plant pathogens. Monitoring. Since there have been reports of soilless media contaminated with fungus gnat larvae, it is a good idea to place potato wedges in a sample of soil and verify that it is clean. Adults can be successfully monitored by using sticky traps throughout the growing zones. Larvae can be observed on the media when they are fully developed. Most larvae can be found in the top inch of the growing media. Control. It is useful to screen windows and doors to prevent fungus gnat entrance. Also adequate irrigation management is important. Control of these flies at home is rarely warranted. Nevertheless if there is a need, two options include Bacillus thuringiensis subspecies israelensis or Steinernema feltiae nematodes. Other options include pyrethroids (such as bifenthrin and permethrin). For commercial operations the following options are available: Biologicals: 1- Bacillus thuringiensis sub. israelensis (Gnatrol). A naturally occurring bacteria produced commercially by fermentation. 2- Hypoaspis miles . A predaceous mite that preys on fungus gnat larvae. Useful at low density levels. 3- Steinernema feltiae. A nematode that is effective at moderate temperatures (60 to 90 F) and moist soil conditions. Several commercial products are available (i.e. Nemasys). 4- Heterorhabditis bacteriophora . Another nematode species that attacks fungus gnat larvae. 5- Atheta coriaria. A rove beetle (Staphylinidae) that feeds on ground dwelling insects. Examples of Distributors of Biological Control Agents: 1- Koppert Biological Systems, Inc 2- Plant Products USA. Representative of Biobest Biological Systems 3- Agrobiologicals In some instances it has been useful to attach large sticky card material to the irrigation booms ( Figure 3 ). Pesticides: When high populations are observed it might be necessary to treat the soil with some insecticides. Always remember to rotate products from different mode of actions groups (see Volume 11; Issue 1; February 2004 from the following address Some suggested products follow (MOA = mode of action group):
REFERENCES Dreistadt, S. H. 2001. Fungus Gnats, Shore Flies, Moth Flies, and March Flies. Oakland: Uni. Calif. Div. Agric. and Nat. Resources. Pub. 7448. Powell, C. C. and R. K. Lindquist. 1997. Ball Pest and Disease Manual. 2nd ed. Ball Publishing, Batavia, Illinois. |
