The water mites are distributed widely through ponds, lakes and mountain streams. In part of their life cycle, larvae of water mites typically attach on adult aquatic insects including hemipterans, odonates, coleopterans, trichopterans, ephemeropterans, plecopterans and dipterans. Most of the information on hostparasite interactions comes from studies of lentic mites and insects, while relatively little is known about the relationships between lotic mites and insects. The purpose of this study is to elucidate the host-parasite interactions between lotic water mite larvae and host insects in mountain streams. We investigate mite attachment on aquatic insects collected at mountain streams in Kanagawa and Shizuoka Prefectures, Japan. Aquatic insects were collected by light-trap and hand-sweeping from May to August 2008. Aquatic insects were identified to species or genus. The parasitic nature of mite larvae on aquatic insects was examined. The distribution of water mite larvae on host insects was analyzed using the Chi Square Test. As a result, a total of 1716 specimens of aquatic insects representing Megaloptera, Trichoptera, Ephemeroptera, Plecoptera and Diptera were collected. Mites were associated with 31.2% of the total number of aquatic insects. Mite larvae in the genus Stygothrombium were associated with Plecoptera. Protzia larvae were associated with Trichoptera and Diptera. Stygomomonia larvae were associated with Trichoptera. Protzia larvae showed a preference for abdomen of Wormaldia sp. [Trichoptera] (P<0.0001, χ²= 133.3631). Protzia larvae however, showed a preference for prothorax of Antocha sp. [Diptera] (P<0.01, χ²=18.3077). Stygomomonia larvae showed a preference for mesothorax and abdomen of Stenopsyche marmorata [Trichoptera] (P<0.0001, χ²=1147.857). From these results, it is considered that mite larvae show certain host preferences for aquatic insects as well as site preferences for the body parts of host insects.

Halacarid mites inhabit mainly in the bottom of the sea and their body lengths are approximately 0.5 mm. Few biological information about halacarids have been obtained. The phylogenetic study of halacarid mites has not been progressed and the phylogenetic relationship within the family Halacaridae is still unknown. Particularly there is no molecular study to infer phylogenetic relationship within the family. In the annual meeting of Acarological Society of Japan 2007, we developed the method for molecular analysis of 28S nuclear ribosomal gene in haracarid mites. Subsequently, we have further progressed the technique of the molecular analysis to infer the phylogenetic relationship of haracarids. The aim of the present study is to elucidate the phylogenetic position of the subfamily Rhombognathinae on the bases of molecular data. Halacarid specimens which were obtained from seaweeds and sandy segment at Japanese seacoasts, consist of eight genera in five subfamilies: Halacarinae (Halacarus sp., Agauopsis spp., Thalassarachna spp.), Halixodinae (Badyagaue sp., Agaue sp.), Copidgnathinae (Copidognathus spp.), Actacarinae (Actacarus spp.) and Rhombognathinae (Rhombognathus spp.). The template DNA was extracted and 28S nuclear ribosomal gene of the DNA was amplified by PCR reactions. And we determined approximately 400 base pair length of the gene. To construct phylogenetic trees by neighbor-joining method we calculated genetic distances of each operational taxonomic unit considering 1) transversions and 2) transitions and transversions based on Tamura - Nei model by using MEGA ver. 4 (Tamura et al. 2007). As a result, we got two trees both showing two main clusters. One of them includes only one subfamily Rhombognathinae and another consist of Halacarinae, Copidgnathnae, Actacarinae and Halixodinae. Rhombognathinae was greatly differentiated from the other subfamilies. Thus, Rhombognathinae possibly is a distinct taxon phylogenetically and this result supports the monophyletic nature obtained previously by morphological analysis.