The life cycles of two bamboo scale insects, Unachionaspis bambusae and Nikkoaspis shiranensis, which are parasitic on the dwarf bamboo, Sasa nipponica, were investigated on Mt. Ohdaigahara, central Japan. U. bambusae and N. shiranensis overwintered as adults. U. bambusae laid eggs from May to July and N. shiranensis from May to August. They had eggs and larvae under their scales and the larvae were found on current leaves in July, suggesting that dispersal occurs from June to July. Consequently, the number of U. bambusae and N. shiranensis per 50 leaves of S. nipponica decreased dramatically from June to July. U. bambusae and N. shiranensis had no eggs under their scales in autumn. These results suggest that U. bambusae and N. shiranensis have one generation a year in Mt. Ohdaigahara.
Recently, the Japanese government has been promoting the thinning of conifer plantations. It is known that Hinoki Cypress (Chamaecyparis obtusa) is susceptible to environmental changes. The authors investigated the risk of occurrence of trees death after heavy thinning of Hinoki Cypress plantations. Twenty-eight stands of heavily-thinned Hinoki Cypress plantations were examined and the rate of dead trees was surveyed by complete enumeration at one of the most severely damaged stands in Kochi Prefecture, southwestern Japan. As a result, the locations where many trees had died were at altitudes below 600 m of south-facing (from southeast to southwest) slopes. More trees had died in the upper part of the slope than in the lower part. It is recommended to avoid heavy thinning of Hinoki Cypress plantations especially in the upper part of south-facing slopes at low altitudes.