Mermithid nematodes are parasites of a wide range of invertebrates but information on their life history associated with their hosts is limited. Here we investigated mermithids isolated from the shield bug Parastrachia japonensis, a univoltine and sedentary insect, to understand their life cycles and the effect of parasitism on their host. Mermithids were detected from 5 out of 6 sampling locations with infection ratios of 0% to 16.1%. Most cases were monoparasitism but hyperparasitism was also observed. Mermithids emerged from the host late in the final host nymphal stage and the host immediately died after the mermithid emerged. No mermithid was detected from adults in the present survey. There was no correlation between weights of hosts and mermithids. In addition, there was no difference in the weights between the nematode-infected and non-infected hosts, and apparent morphological and behavioral changes were not observed in the nematodeinfected nymphs, suggesting that nematode parasitism does not affect the host before the nematodes emerge. Phylogenetic analysis revealed that two species of mermithids parasitize P. japonensis.

Plant-parasitic nematodes often interact with host plants via chemical compounds to optimize the chance of invasion. Previous research suggests that hatching factors may also be involved in host-searching in nematodes. Here we tested whether solanoeclepin A (SEA), a host-derived hatching factor for G. rostochiensis, was utilized as a host-searching cue by second-stage juveniles (J2s). A two-choice bioassay using a rectangular Petri dish containing soil was performed to observe nematode responses. The SEA concentrations tested (0.01, 0.1, 1 and 10 ppb) were known to be suitable for hatching and were assumed to correlate to the concentrations around cysts in soil. When J2s were placed between soil moistened with potato root diffusate (known to attract G. rostochiensis J2s) and water-moistened soil, a significantly larger number of J2s chose diffusate-treated soil. However, J2s did not discriminate between soil treated with SEA and soil treated with solvent only. These results suggest that G. rostochiensis J2s do not use SEA as a hostsearching cue.

Dagger nematodes (Xiphinema spp.) were detected from nine tree species in a survey conducted in three Japanese prefectures, Chiba, Saitama and Fukuoka, producing Japanese traditional ornamental trees. For PCR diagnosis of these nematodes, we designed six speciesspecific primer pairs on the basis of a known sequence of COI region of mtDNA and a known sequence of 18S small subunit to ITS1 region of rDNA. The specificity of the six designed primer pairs was confirmed from the fact that only target species or a related species was PCR amplified. As results of species-specific PCR and a BLAST search of sequences of D2–D3 expansion segments of 28S rDNA, surveyed nematodes were estimated to be X. brevicolle, X. insigne, X. parachambersi or X. hunaniense. Additionally, a primer set of multiplex PCR for comprehensive amplification of these four species and two other species (Xiphinema sp., X. bakeri) was developed.