Abstract
Regular survey of soil insects and some other arthropods were carried out in a mixture forage sward which was sown before five years. From March of 1966 to January 1967, once a month, four replicated soil samples (50sq.cm×20cm deep) were taken, and numbers of larvae or adults were counted, identified, and recorded at each collecting date. Recorded species were as follows. Insecta; 61 in Coleoptera, 6 in Hymenoptera, 3 in Orthoptera and in Diptera, 1 in Hemiptera, in Collembora and in Lepidoptera. Crustacea; 1 in Isopoda and in Polydesmoidea. Total number of these arthropods species was abundant in winter but decreased in summer. Among them, about 10 species belonging to Coleoptera and 1 species belonging to Curstacea were the harmful for forage plants. Most larvae of Coleoptera were found in the soil throughout the year, and did not show seasonal fluctuation. Exceptionally the larva of Colposcelis signata Motsch. was found only in summer, from July to August and a large larval population peak of Sitona hispidula Fab. was observed in May. As to vertical movement of soil insect, a population density of larvae was the highest in the first top soil (a depth of 0-5cm) during the season from March to October. The larvae slightly moved downwards from late autumn to winter but not so deep. From this observation it is able to say that the vertical movement of the larvae in a pasture field is less than that in other crops field such as tree nursary, and the field of wheat and upland rice plants.
