キャベツ畑でのモモアカアブラとダイコンアブラとの個体群の成長について

抄録

(1) Investigations on the aphid population were made in a cabbage field at Nogi, Matue City, from late April to early June in 1956. The species recorded during this period were Myzus persicae, Brevicoryne brassicae and Rhopalosiphum pseudobrassicae. The last mentioned species was rare. (2) There was a remarkable difference in the pattern of distribution of aphids on a cabbage leaf between M. persicae and B. brassicae : In the case of M. persicae the aphids were scattered on a part of the leaf (sometimes all over the undersurface of the leaf), while in the case of B. brassicae the colonies were built up tightly and these were scattered. (3) It seems that the distribution of the aphid in a cabbage field had a correlation with the direction of the prevailing wind in the spring. (4) M. persicae shows a preference to the leaves at the lower part of the plant. On the contrary, the colony of B. brassicae is apt to build up in the upper part of the plant, excepting the part at which the leaves are bulbed up. (5) Winged forms of M. persicae came flying to the cabbage field from the end of April, but the population growth was restrained by severe circumstances until about the 10th of May. On the plants which aphid populations were growing favorably, these were sudden increases of aphid numbers at about the 20th of May, when many aphids reached maturity and many individuals of the new generation were produced. (6) Winged forms of B. brassicae did not seem to fly to the cabbage field before the beginning of May. The populations of this species also made sudden growth at about the 20th of May on the plants which the aphid populations continued to grow smoothly from about the 10th of this month. On the plant having a large population at the 4th of June, many colonies were built up in the lower part and on the part at which the leaves are bulbed up as well as in the upper part. (7) In both species there were some number of individuals which were attacked and swelled up by parasites, when the investigation was made on the 4th of June.