Rove beetles for fungus gnat
Rove beetles hunt where fungus gnat larvae live, in damp compost and organic debris, and in Dalotia coriaria both adults and larvae eat them. On a windowsill the wild ones are incidental; in a greenhouse or propagation house they are worth encouraging, and Dalotia is released deliberately for the same job. They are easily taken for earwigs, which have pincers at the tail and are a mixed blessing in a garden.
Before you act
Slender beetles with wing cases so short that most of the abdomen is bare, so they look more like an earwig than a beetle. Most hunt tiny prey in compost, leaf litter and topsoil. One member of the family, Dalotia coriaria, is sold as a greenhouse biocontrol; the rest arrive on their own. How to recognise it, what it is confused with and how to keep it around are on the full Rove beetles profile.
Other controls for fungus gnat
- Steinernema feltiaeNematode · 250k–500k /m² of compost surface; about 5 million per 25 houseplants
- Stratiolaelaps scimitusPredatory mite · 100–500 /m² of compost surface (Dragonfli: 100 preventive, 500 on a heavy infestation)
- Bacillus thuringiensis israelensisMicrobial insecticide · Label rate — Gnatrol home label 1–1.5 tsp per gallon of water as a soil drench, wetting the compost surface; Mosquito Bits sprinkled over the compost and watered in
- Dalotia coriariaPredatory rove beetle · 0.1–2 /sq ft (about 1–22 /m²); suppliers differ
- Macrocheles robustulusPredatory mite · 100–500 /m² per release, repeated once or twice