The Japanese cedar bark midge, Resseliella odai sometimes severely hampers timber production of the Japanese cedar, C'ryplomeria japonica mainly in Kyushu. The presence of larvae is associated with fleck marks on the phloem. In some cases cambium layer under the fleck is stained and engulfed in the xylem, and the commercial value of the injured timber is reduced. The occurrence of R. odai and the percentage of injured trees were surveyed in November 1986 at 20 stands of the Japanese cedar plantation in Kagoshima Prefecture. At each stand 50 trees were examined to observe the fleck marks on the phloem, and environmental conditions of the stands were recorded. The bark midge was found at all the 20 stands, and the percentage of injured trees ranged from 4 to 100%. There was a tendency for the percentage to increase at a stand which was characterized by the following combination of growing conditions, location and management: relatively dense stand (over 2, 500 trees/hectare), consisting of younger(shorter and thinner) trees which had not been pruned, located in a valley near a stream, on a slope facing the northeast, north or northwest directions, ground being covered rather densely by low-growing plants. This sort of analysis of environmental conditions is considered to be useful for the control of the bark midge population by modifying the habitat favourable for the bark midge.