Fungus gnat

Short description: Group of insects

Fungus gnats

Sciaridae spp.
Scientific classification
Kingdom:  | Animalia
Phylum:  | Arthropoda
Class:  | Insecta
Order:  | Diptera
Infraorder:  | Bibionomorpha
Superfamily:  | Sciaroidea
Groups included

Sciaridae
Diadocidiidae
Ditomyiidae
Keroplatidae
Bolitophilidae
Mycetophilidae
Cladistically included but traditionally excluded taxa

Mosquitoes (gall midges)

Fungus gnats are small, dark, short-lived gnats, of the families Sciaridae, Diadocidiidae, Ditomyiidae, Keroplatidae, Bolitophilidae, and Mycetophilidae (order Diptera); they comprise six of the seven families placed in the superfamily Sciaroidea.

## Contents

* 1 Description
* 2 Hardiness
* 3 Management
* 3.1 Insecticides
* 3.2 Biological control
* 3.3 Soaps, fly traps, and other methods
* 4 See also
* 5 References

## Description

The larvae of most species feed on fungi growing on soil, helping in the decomposition of organic matter. However, some species are predatory, including those in the genus Arachnocampa of family Keroplatidae – the "glowworms" of Australia and New Zealand.[1]

The adults are 2–8 millimetres (0.08–0.3 in) long, and are occasionally pollinators of plants and carriers of mushroom spores.[2] They also may carry diseases such as pythium (which causes "damping-off" to kill seedlings) on their feet.[3]

Most fungus gnats are weak fliers, and can often be seen walking rapidly over plants and soil, rather than flying. However, when airborne, the gnats may be quite annoying to humans by flying into their faces, eyes, and noses, both indoors and outdoors.[4][5] These flies are sometimes confused with drain flies.[6]

This species goes through 4 stages of life: egg, larva, pupa, and adult.[7] The adults can live up to 10 days and lay up to 200-300 eggs[8] at a time in the moist top layer of the soil. These eggs will typically hatch within 4 days and progress through the cycle. The pupa stage also consists of about 4 days, then adult gnats emerge and begin the whole process again.[9]

## Hardiness

Some fungus gnats are exceptionally hardy, being able to tolerate cold conditions through their possession of antifreeze proteins. Typically, overwintering organisms can either avoid freezing or tolerate freezing, but Exechia nugatoria can do both. For E. nugatoria, the production of noncolligative antifreeze proteins (NAPs) protects 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. By allowing the abdomen to freeze, evaporative water loss is reduced over the course of the winter.[10][11]

## Management

Fungus gnats in the family Sciaridae may be pests. They are typically harmless to healthy plants - and humans - but can inflict extensive damage to seedlings; their presence can indicate more serious problems. In houseplants, the presence of sciarids may indicate overwatering; they may be feeding on roots that have been immersed in water too long and are thus rotting, or the gnats may be attracted to fungus growing in saturated topsoil. Consequently, allowing the top two inches of soil[12] to dry may reduce their numbers.[13] The pests are sometimes also managed by placing a layer of sand[14][15] pebbles,[16] or indoor mulch on top of the soil around plants. Adding perlite or another similar soil conditioner can also help aerate the soil and improve drainage, both of which will reduce the growth of the fungi which the gnats feed upon. [17]

### Insecticides

Pyrethrins and the similar pyrethroid compounds are known to have insecticidal properties, including against fungus gnats.[18] Related pyrethroid insectides have also been used. Pyrethrin compounds are known to occur in certain chrysanthemum flowers.

Commercial greenhouses typically employ the insect growth regulator diflubenzuron for control of fungus gnats and their larvae. It is applied to infected soil and will kill fungus gnat larvae for 30–60 days from a single application. Its mechanism of action is to interfere with chitin production and deposition and it also triggers insect larvae to molt early without a properly formed exoskeleton, resulting in the death of the larvae. Although it is targeted at fungus gnat larvae, care should be taken in applying it as it is highly toxic to aquatic invertebrates. Diflubenzuron typically has no toxic effect on adults; only the larvae are affected.[19][20]

### Biological control

Various methods of controlling or eliminating fungus gnats with biological pest control have been developed. For example, Bacillus thuringiensis israelensis (BTI) is known to produce proteins that can kill fungus gnats larvae and some other insects like mosquitos.[21][22][23][18] BTI is a naturally occurring bacteria that has been used for decades—the United States EPA reports that it has no toxicity to humans.[21] Several dozen products containing BTI have been approved for residential, commercial, and agricultural use in the United States.[21] The israelensis subspecies is suggested because other types of Bacillus thuringiensis (BT), such as those for controlling caterpillars, are ineffective at controlling fungus gnats.[18]

Steinernema nematodes have been used to control fungus gnats, including in combination with BTI.[18][23] These nematodes, including the feltiae species, are parasites that can attack the larvae stage of fungus gnats.[24]

Mites of the species Stratiolaelaps scimitus (formerly known as "Hypoaspis miles") have also been shown to be effective at controlling fungus gnats.[18] These scimitus mites are a natural predator that eat fungus gnat eggs and small larvae.

### Soaps, fly traps, and other methods

Other methods for controlling fungus gnats include drenching the soil annually in an insecticidal soap. Hydrogen peroxide can be mixed with water and used to kill fungus gnat larvae in infected soil with a mixture of one part 3% hydrogen peroxide mixed with four parts water, then applied to the soil.[5][6] Adults can be trapped with sticky traps made of yellow card stock or heavy paper coated in an adhesive since the adults are attracted to the color yellow.[25][26]

Since the gnats are weak fliers, fan-based traps as well as other fly-killing devices may be used to help control free-flying gnats, especially indoors. There are a number of toxic and non-toxic methods of controlling sciarids and their larvae, including diatomaceous earth, powdered cinnamon,[5] or by placing smells they dislike around the plant such as dryer sheets or oils like lavender and peppermint.[27]

To investigate how bad the infestation possibly is, one can place cut-up pieces of potato onto the topsoil, and let them sit for about 72 hours.[28] The larvae will begin to feed on them within the week. Check every few days, pulling out larvae-covered potato pieces.[29]

## See also

* Drain fly

## References

1. ↑ Morris, Lulu. "HAVE YOU SEEN THE DAZZLING GLOWING WORMS OF AUSTRALIA AND NEW ZEALAND?". http://www.nationalgeographic.com.au/australia/have-you-seen-the-dazzling-glowing-worms.aspx.
2. ↑ "Ko Mochizuki, Atsushi Kawakita. Pollination by fungus gnats and associated floral characteristics in five families of the Japanese flora. Annals of Botany. Volume 121, Issue 4, Pages 651–663". 14 March 2018. https://academic.oup.com/aob/article/121/4/651/4781678.
3. ↑ "Ecogrow Fungus Gnat". 17 March 2014. Archived from the original on 23 April 2010. https://web.archive.org/web/20100423004651/http://www.ecogrow.com.au/top10/Fungus_Gnat.html.
4. ↑ Fungus Gnats (advice)
5. ↑ 5.0 5.1 5.2 "Controlling Fungus Gnats and Damping Off Organically". 8 April 2012. http://www.smallfootprintfamily.com/controlling-fungus-gnats-organically.
6. ↑ 6.0 6.1 "11 Sure Ways of Getting Rid of Gnats". February 23, 2016. http://www.coverimages.org/11-sure-ways-of-getting-rid-of-gnats/.
7. ↑ "25+ Ways to Get Rid of Gnats Inside & Outside the House" (in en-US). https://www.fliesonly.com/how-to-get-rid-of-gnats-inside-house-kitchen-outside/.
8. ↑ "Weapons of Gnat Destruction: The Ultimate Guide to Killing Fungus Gnats" (in en). 2022-03-03. https://www.learningwithexperts.com/gardening/blog/weapons-of-gnat-destruction-the-ultimate-guide-to-killing-fungus-gnats.
9. ↑ Hale, Frank (2011-11-22). "SP341-C Insects: Fungus Gnats". University of Tennessee Research and Creative Exchange 1. https://www.academia.edu/102549972.
10. ↑ "Fungus gnats survive winter half frozen". http://www2.gi.alaska.edu/ScienceForum/ASF19/1960.html.
11. ↑ Sformo, Todd; Kohl, F.; McIntyre, J.; Kerr, P.; Duman, J. G.; Barnes, B. M. (1 October 2009). "Simultaneous freeze tolerance and avoidance in individual fungus gnats, Exechia nugatoria". Journal of Comparative Physiology B 179 (7): 897–902. doi:10.1007/s00360-009-0369-x. PMID 19495776.
12. ↑ "Fungus Gnats: treatment prevention and management" (in en). 2022-05-22. https://www.lebotanist.com.au/blogs/greenerygazette/fungus-gnats.
13. ↑ W.S. Cransaw and R. A. Cloyd. "Fungus Gnats as Houseplant and Indoor Pests". 2009.
14. ↑ Jan Riggenbach."Fungus gnats and plants don’t mix".
15. ↑ John Brittnacher."Pests – Fungus Gnat Larvae"
16. ↑ "Fungus Gnats: Treatment, prevention and management". https://www.lebotanist.com.au/blogs/news/fungus-gnats.
17. ↑ "How I Got Rid of Fungus Gnats—For Good". 2024-12-19. https://gardenbetty.com/fungus-gnats/.
18. ↑ 18.0 18.1 18.2 18.3 18.4 "Fungus Gnats Management Guidelines--UC IPM". http://ipm.ucanr.edu/PMG/PESTNOTES/pn7448.html.
19. ↑ ADEPT Insect Growth Regulator
20. ↑ Adept label
21. ↑ 21.0 21.1 21.2 "Bti for Mosquito Control". 5 July 2016. https://www.epa.gov/mosquitocontrol/bti-mosquito-control.
22. ↑ "I have fungus gnats everywhere. Can you help?". 20 January 2021. https://extension.oregonstate.edu/ask-expert/featured/i-have-fungus-gnats-everywhere-can-you-help.
23. ↑ 23.0 23.1 "Fungus Gnats". https://ohioline.osu.edu/factsheet/ENT-59.
24. ↑ "Biological Control: Using Beneficial Nematodes". 6 March 2015. https://ag.umass.edu/greenhouse-floriculture/fact-sheets/biological-control-using-beneficial-nematodes.
25. ↑ "How to Get Rid of Fungus Gnats – Planet Natural". https://www.planetnatural.com/pest-problem-solver/houseplant-pests/fungus-gnat-control/.
26. ↑ "Controlling Fungus Gnats Organically – Small Footprint Family". 8 April 2012. https://www.smallfootprintfamily.com/controlling-fungus-gnats-organically.
27. ↑ University, Yeshiva; Michigan, University of. "How to Get Rid of Gnats Naturally and Keep Them Away" (in en). https://www.treehugger.com/how-to-repel-gnats-naturally-4864050.
28. ↑ Lindquist, Richard. "Integrated Management of Poinsettia Pests: Fungus Gnats". Southeastern Floriculture. https://hortscans.ces.ncsu.edu/uploads/i/n/integrat_51e4518bd3a73.pdf.
29. ↑ "How to Get Rid of Fungus Gnats Effectively (Complete Guide)" (in en-US). https://www.planetnatural.com/pest-problem-solver/houseplant-pests/fungus-gnat-control/.

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