Abstract
In 1963 and 1964 observations were made to ascertain the influence of the predation of Orius sp. on the aphid population in a soy-bean field at Morioka. Orius sp. increased rapidly from mid July to late August or early September, and fed mainly on aphids (Aphis glycines and Aulacorthum solani), spider mites (Tetranychus kanzawai, etc.), and less frequently on thripids (Taeniothrips glycines and Thrips hawaiiensis?, etc.) in the field. Dispersion of adults of the predator from the soy-bean field seemed to occur after soy-bean plant reached maximum growth. In 1963 the populattion of A. glycines was diminished by the predation of Orius sp. in early August, but it gradually recovered in parallel with increase of tetranychid, which is one of the principal preys of Orius sp. On the other hand, A. glycines multiplied towards August without any temporal decrease in the population in 1964, when an early outbreak of the tetranychid was observed. Every year Aulacorthum solani received profound predacious effect due to Orius sp., but gradually increased towards September. These phenomena were discussed in relation to the relative abundance in the principal preys of Orius sp. and their behaviour.
