Mermithid nematodes isolated from the shield bug Parastrachia japonensis

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.