The pinewood nematode (Bursaphelenchus xylophilus) is known to be the causative agent of pine wilt disease, which is transmitted from wilt-killed to healthy pine trees by the insect vector Monochamus alternatus. The second-stage propagative juvenile develops into third-stage dispersal (J_III) or propagative juveniles. The J_III develops into the fourth-stage dispersal juvenile (J_IV), a special stage for transportation, then the J_IV enters the tracheal system of adult beetles in pupal chambers in the xylem. To determine the differences in some life history parameters related to transmission between a virulent and an avirulent isolate of B. xylophilus, progression to the different life stages was investigated using two nematode isolates of different virulence, M. alternatus larvae, and pine bolts with an artificial pupal chamber. The numbers of J_IIIs and J_IVs produced around the pupal chamber by the time of beetle emergence were much smaller in the avirulent isolate than in the virulent one. The proportion of J_IIIs produced in a population around the pupal chamber (the J_III and J_IV number/the total population) and the probability of J_IIIs developing into J_IVs (the J_IV number/the J_III and J_IV number) were also smaller in the avirulent isolate. Although the probability of J_IVs boarding beetles (the initial nematode load/the J_IV number) was equal between the two isolates, the mean initial nematode load was much smaller in the avirulent isolate. The smaller initial nematode load of the avirulent isolate was ascribed to its smaller rate of reproduction and to lower production rates of J_III and J_IV. A trade-off between the virulence and transmission rate of B. xylophilus is discussed herein, taking into account the effect of the initial nematode load on the vector’s longevity and flight performance.

Deladenus nitobein. sp., a parasite of a woodwasp species,Sirex nitobei, is described based on its typological characters and molecular profiles of part of the small subunit D2-D3 expansion segments of the large subunit and internal transcribed spacer region of the ribosomal RNA gene, as well as part of the mitochondrial cytochrome oxidase subunit I (mtCOI) gene. Adult host woodwasps emerging from dead Japanese red pine logs,Pinus densiflora, collected at Aomori, Japan, were dissected and examined for nematode association. The new species was isolated from the body cavity and reproductive system ofS. nitobeias large parasitic females and small parasitic juveniles. The nematodes were cultured successfully on 1.0% malt extract agar medium, inoculated withSirex-associated fungus,Amylostereumareolatum. The mycophagous adult nematodes were characterised by the relative position of the excretory pore, located at 25 (19-28) and 25 (18-30)μm anterior to the hemizonid in the male and female, respectively, and a broad female tail with a rounded distal end. Typologically, the new species forms a cryptic species complex withD. siricidicolaandD. canii. In addition, the new species andD. siricidicolashare the same host wasp, tree and fungal species in Japan. However, the cryptic species can be separated from each other based on the described morphological and molecular sequence differences in the mtCOI gene.

The parasitism of two groups of host-manipulating parasites of hornets was examined in Kyoto, Japan. Vespa mandarinia (661 individuals), V. simillima (303), V. analis (457), V. ducalis (158), V. crabro (57), and V. dybowskii (4) were collected either by bait trap or hand collection with an insect net, and examined for their parasites. An endoparasitic nematode, Sphaerularia vespae was isolated from three overwintered gynes of V. mandarinia and a gyne of V. ducalis. While endoparasitic insects, Xenos spp., were recovered from 13 V. mandarinia, 77 V. analis, two V. ducalis, and three V. crabro, and those recovered from V. analis and others were molecularly identified as X. oxyodontes and X. moutoni, respectively. Comparing Xenos parasitism level and capturing methods, the parasitism level was significantly higher in trapped hosts than in hand-collected ones, suggesting that stylopized hosts are more strongly attracted to the food source (bait trap) compared with unparasitized hosts. The genotypes of S. vespae were identical to each other, and near identical to its type population. While each of the two Xenos spp. showed four mitochondrial DNA haplotypes. A phylogenetic comparison suggested that Xenos haplotypes found in the present study are close to those previously reported from Japan and other Asian countries.

Summary: Contortylenchus genitalicola is a unique species within the genus. It parasitises the ovary or testis of the longhorn beetle, Monochamus alternatus, and has a neotylenchid-like culturable mycetophagous phase within its life cycle, while the other species in the genus parasitise bark beetles and have a typical unculturable allantonematid life cycle. Because the species was described based solely on morphology, it was necessary to confirm the phylogenetic and taxonomic status of C. genitalicola. A molecular phylogenetic analysis of the species based on ribosomal RNA sequences revealed that C. genitalicola forms a well-supported clade with Contortylenchus spp. isolated from bark beetles, an unidentified allantonematid from Iran, and ‘Deladenus cf. laricis’ isolated from the metallic wood-boring beetle, Agrilus macer LeConte (Coleoptera: Buprestidae), in the USA. The generic status of C. genitalicola was supported by phylogenetic analysis, and the analysis also suggests that the diversity of the genus could be higher than currently expected.