Entomopathogenic nematodes

Steinernema feltiae , Steinernema carpocapsae and Heterorhabditis bacteriophora

Entomopathogenic nematodes are microscopic roundworms that parasitize soil-dwelling pest stages, including the larvae of fungus gnats (Family Sciaridae), shore flies  (Family Ephydridae), and some pest beetles (e.g. black vine weevil (Otiorhynchus sulcatis) and some turf-feeding scarabs. They are not harmful to plants_

Different species differ in their host range, environmental tolerances, and in the distance they will move to find hosts. These factors should be carefully considered when selecting which species to use.  For example, Steinernema carpocapsae is relatively sedentary and tends to remain near the soil surface to ‘ambush’  its hosts, whereas S. feltiae will search more actively through the substrate.
Nevertheless, S carpocapsae has sometimes been found parasitizing hosts relatively deep in the soil, and it has been suggested that larger roots may serve  as ‘pathways’ that can facilitate its movement through the soil.

Entomopathogenic nematodes are supplied as infective juveniles, which are usually applied as a soil drench (sometimes through irrigation lines if flow rates are adequate). Nematode movement through the soil is limited to a few centimeters per day and requires adequate moisture; it may be necessary to irrigate prior to application and again afterwards to allow the nematodes to move into the upper soil layers where there is less risk of desiccation. Nematodes can be killed by exposure to direct sunlight, and ideally  they should be applied under cloudy conditions or in the evening.

On contacting a suitable host, the juvenile nematodes enter the body cavity
through the mouth, anus, or spiracles; once inside, they release symbiotic bacteria that
multiply rapidly and usually kill the host within 1-3 days. The nematodes  feed,
mature and reproduce within the dead host until the latter eventually ruptures, releasing
thousands of new infective juveniles to continue the process. Depending on environmental conditions and the host species, this may take approximately 2-3 weeks. If no suitable hosts are present at that time, the nematode population will rapidly decline. Insect larvae and pupae killed by Steinernema species typically turn a yellowish-tan or brown color, while those infected by Heterorhabditis tend to take a reddish hue.

Steinernema carpocapsae is most effective at soil temperatures between 22-28°C (72—82°F); S. feltiae can remain infective at soil temperatures as Iow as 10°C (50°F), but development is faster at higher temperatures (up to 30°C/86°F).

Minimum soil temperatures for Heterorhabditis bacteriophora are 12-15°C(54-59°F),