Five new species of Deladenus parasitizing siricid woodwasps from world wide sources are described in detail and their differences from other species of the genus are given. A key to the seven species of Deladenus known to parasitize siricids is included. The biology of these nematodes involves two life cycles associated with profound functional dimorphism of adult female nematodes and of spermatozoa. One cycle is parasitic with a sphaerulariid form of female reproducing ovoviviparously within the haemocoel of various siricids and the other is free living involving a neotylenchid form of female that reproduces oviparously while feeding on the symbiotic fungus within coniferous timber. Parasitism by three of the five new species of nematode results in sterilization of their female hosts; another species does not sterilize its only known host, while the other varies in its effect depending on host species.
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R.A. Bedding (1974) studied this question.