Deladenus wilsoni n.sp. and D. siricidicola n.sp. (Neotylenchidae), entomophagous-mycetophagous nematodes parasitic in siricid woodwasps.

Deladenus wilsoni n. sp. and D. siricidicola n. sp. are described in detail and their differences from other species of the genus are given. Both species have strongly dimorphic females; one form, which feeds and reproduces in coniferous timber on the symbiotic fungus of siricid woodwasps is typical of the genus Deladenus (Neotylenchidae), and the other, which penetrates the insect larva and reproduces in the insect haemocoel, is typical of the family Allantonematidae. The morphological differences between the two forms throw doubt on the phylogenetic validity of several characters used in nematode taxonomy, particularly in this group.