During extensive field surveys, Holobuskashmiricus beneficus (Naomi) (Coleoptera: Staphylinidae), a prospective natural enemy of spider mites, was recorded for the first time in the Ryukyu Archipelago, while it was not found in Taiwan. On the other hand, another related species, H. yasumatsui (Kistner), was not detected in the Ryukyu Archipelago, but instead was found only in Taiwan. These distributions indicated that species composition varies in the two geographical areas. Holobus kashmiricus beneficus co-occurred with more than six spider mite species (Acari: Tetranychidae) in the Ryukyu Archipelago, suggesting that this species has a broad prey range. Here, we redescribed the two rove beetle species, because the intraspecific variation among the previous diagnostic morphological characters, such as patterns and numbers of carinae on abdominal tergites IV–VI, prevented their use in the definitive classification of the species. We suggest that the shapes of the antennal segment VII and abdominal segment VIII should be considered as new diagnostic characters for H. kashmiricus beneficus and H. yasumatsui.
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