What do fungus gnats eat

AMES, Iowa — Do you ever notice the occasional small fly in the sink, or sometimes on the lighted screen of a laptop in the evening?

However, now that many people are working from home, things that were easily forgotten annoyances have suddenly become really big annoyances that must be solved immediately. So, if you are in the same boat, read on to get your questions answered about flies breeding in the house and what you can do about it. What does breeding indoors mean? In general, for insects, it means that adult insects are mating; the females are finding a good place to lay their eggs; the eggs are hatching into larvae that are finding something to eat and they grow.

Once larvae are full grown they transform into pupa. The pupal stage is where the larvae transforms into the adult. Adult insects often have wings and fly around the house, so this is usually what we human inhabitants of the house notice. How do you know insects were breeding in the house? Because winters in the Midwest are too cold outdoors for insects to be active and breed. Seeing live insects over many months indoors is a pretty good sign they are reproducing in the house. The key is to find what the larvae are eating.

It is no use trying to kill adult insects unless you can kill all females before they lay eggs this is impossible. So, although the adults are irritating and what you actually see, you have to do some detective work to find out where the kids are hiding!

OK, how do you find out where the insect is breeding? The first step is to identify the insect, because then we will know what the kids larvae eat and therefore where to look. In my case, I identified my flies as fungus gnats. Adult fungus gnats lay their eggs on fungus or in soil.

When the larvae emerge from the eggs, they burrow into the material they were born on. This could be a wild mushroom, or it could be a house plant root. The larvae feed on the insides of the mushroom for around two weeks, then they crawl out and go into the pupal stage. The adults appear about four days later. It is during the larval stage that most damage is caused to greenhouse and indoor plants. Their long antennae distinguish them from the more robust shore flies, which are also found in greenhouses, associated with algae and decomposing organic matter, but have short bristle-like antennae.

Wings are light gray to clear, and the common Bradysia species have a Y-shaped wing vein. Because adult fungus gnats are attracted to light, you first might notice these pests flying near windows indoors.

Fungus gnats often remain near potted plants and run across or rest on growing media, foliage, compost, and wet mulch piles. Females lay tiny eggs in moist organic debris or potting soil. Larvae have a shiny black head and an elongated, whitish-to-clear, legless body. They eat organic mulch, leaf mold, grass clippings, compost, root hairs, and fungi. If conditions are especially moist and fungus gnats are abundant, larvae can leave slime trails on the surface of media that look like trails from small snails or slugs.

Larvae, however, when present in large numbers, can damage roots and stunt plant growth, particularly in seedlings and young plants.

Significant root damage and even plant death have been observed in interior plantscapes and in houseplants when high populations were associated with moist, organically-rich soil. Thus, a houseplant that is wilting may not indicate a lack of water, but rather root damage by fungus gnat larvae or more commonly other causes of unhealthy roots. However, too much or too little water, root decay fungi, and improper soil conditions e.

Serious fungus gnat damage is more common in greenhouses, nurseries, and sod farms. Fungus gnats develop through four stages —egg, larva with four larval stages or instars , pupa, and adult. The tiny eggs and oblong pupae occur in damp organic media where females lay eggs and larvae feed. A generation of fungus gnats from female to female can be produced in about 17 days depending upon temperature.

The warmer it is, the faster they will develop and the more generations will be produced in a year. Fungus gnats have many overlapping generations each year. Outdoors, they are most common during winter and spring in interior areas of California, when water is more available and cooler temperatures prevail. They can occur during any time of the year in moist coastal regions and indoors. Physical and cultural management tactics—primarily the reductions of excess moisture and organic debris—are key to reducing fungus gnat problems.

Commercially-available and naturally-occurring biological control agents can also control this pest. Visual inspection for adults usually is adequate for determining whether a problem exists.

You will see adults resting on plants, soil, windows, or walls, or you might see them in flight. Besides looking for adults, check plant pots for excessively moist conditions and organic debris where larvae feed. Yellow sticky traps can be used to trap adults.

Chunks of raw potato placed in pots with the cut sides down not the peels are sometimes used to monitor for larvae. Because fungus gnats thrive in moist conditions, especially where there is an abundance of decaying vegetation and fungi, avoid overwatering and provide good drainage.

Allow the surface of container soil to dry between waterings. Clean up standing water, and eliminate any plumbing or irrigation system leaks. Moist and decomposing grass clippings, compost, organic fertilizers, and mulches are also favorite breeding spots.

Avoid using incompletely-composted organic matter in potting media unless it is pasteurized first, because it will often be infested with fungus gnats. Improve the drainage of the potting mix e.

Minimize organic debris around buildings and crops. Avoid fertilizing with excessive amounts of manure, blood meal, or similar organic materials. Screen and caulk leaky windows and doors to help prevent pests from coming indoors.

In some cases you may wish to toss out severely infested plants. Purchase and use only pasteurized container mix or potting mix.