steinern

Steinern is a genus of entomopathogenic nematodes, microscopic roundworms that parasitize insects. These nematodes belong to the family Steinernematidae. They are commonly known as steinernematids. Steinernematids are obligate parasites, meaning they require a host insect to complete their life cycle. They are often used as biological control agents against insect pests in agriculture and forestry.

The life cycle of steinernematids involves both a free-living stage and a parasitic stage. In their free-living stage, they are found in soil and leaf litter. When an insect host comes into contact with the infective juvenile (IJ) stage of the nematode, the IJ enters the host, typically through natural openings like the mouth, anus, or spiracles. Once inside, the IJ seeks out the insect's hemocoel, the body cavity. Upon reaching the hemocoel, the IJ emerges from its sheath and infects the insect. Crucially, steinernematids carry symbiotic bacteria, usually from the genus Xenorhabdus, within their gut. These bacteria are released into the insect's hemocoel, where they multiply rapidly. The bacteria break down the insect's tissues, feeding the nematodes and killing the host within a short period, often 24 to 48 hours.

The steinernematid nematodes then feed on the bacteria and the liquefied insect tissues, undergoing several molts to reach adulthood. Adults reproduce, and females lay eggs. The offspring develop through larval stages and eventually form infective juveniles, which emerge from the dead insect in search of new hosts. The symbiotic bacteria are also carried by the infective juveniles, ensuring they are available to inoculate the next host. This mutualistic relationship between the nematode and the bacterium is essential for successful parasitism. Different species of Steinernema have varying host ranges, making them valuable for targeted pest control.