Nematodes are small, colorless, cylindrical round worms that occur naturally in soils throughout the world. Different species work best against different target pests. Steinernema feltiae is primarily used against fungus gnat larvae, but also used to combat thrips pupae in the soil.
The nematodes enter the insect host through body openings. They multiply within the host and release a symbiotic bacterium whose toxin kills the fungus gnats. The larvae are killed in one to two days by blood poisoning. More than one generation of nematodes may develop in dead host insect in the media. The infective juveniles then exit the dead body and search for new hosts to infect.
Nematode applications do not require masks or other safety equipment. And re-entry time, residues, groundwater contamination, chemical trespass, and pollinators are not issues. Most biologicals require days or weeks to kill, yet nematodes, working with their symbiotic bacteria, can kill insects within 24-48 hours.
S. feltiae is sold under several trade names and are labeled as a soil drench treatment against fungus gnat larvae. Preventive applications to moist soils work best. Nematodes are compatible with a number of different pesticides. However, they are generally not compatible with organophosphates, carbamates, nematicides and hydrogen dioxide. Do not mix nematodes with your fertilizer solution.