Green peach aphid (Myzus persicae SULZER) is one of the most important pests of curciferous vegetables in Japan. It is seriously injurious to Daikon, cabbage and Petsai. Such leaves aregenerally crowded with this aphid : green, yellow and pink aphids, some winged, others wingless, and of several sizes. Green and pink forms in this paper were started from two wild colonies collected in Utsunomiya and Tokyo. The aphids were reared in a large glasshouse (average temperature 13℃) or in greenhouse (average temperature 25℃) during 1951 (except summer) and in the spring of 1952. Individual rearing. The colour variation of two coloured forms reared on a piece of cabbage leaf in a small cup was very stable under the same rearing conditions. For instance, 726 of green form and 297 of pink form of the offspring of initial female all maintained their own colour. Otherwise, the green form showed that the nymphal period was shorter and the reproductive number of young per day was larger than the pink form. Mass rearing. In 1952,the author studied the leaf-by-leaf distribution and the reproductive number of young between the green and pink forms on the potted young cabbage. The degrees of the age of leaves are distinguished on external appearance alone. [table] Figures 1 and 2 show the leaf-by-leaf distribution of the green form (open blocks) and pihk form (solid blocks) on different plants. Fig. 1 showed the results of rearing in the greenhouse (average 25℃) and Fig. 2 showed the results of rearing in the glasshouse (average 13℃). The age of each leaf at the time of counting the aphid are indicated by the length of the horizontal line on the same plants. In the greenhouse, at first, the green form was extremely dence on the younger leaf of growing plants and the pink form was sparsely crowded on the older leaf. But later, a new colony of the green form is extended on the middle and mature leaves but not the pink form.Otherwise, the number of both forms are gradually increased on the potted cabbages until the aphids are crowded to the saturation point and then a few winged or nymphs are produced by wingless female. But in the glasshouse, they did not develop into a heavy infestation like the above. And between the green and the pink form the leaf-by-leaf distribution was not clear as on the above items. The third figure gives the same results in the greenhouse at the next rearing. The Figs. 4 and 5 show that light infestations of the green and the pink form develop simultaneously on same plant, which permits a direct comparison of the distribution of the two forms in relation to leaf age. The leaf-by-leaf densities of the two forms showed that the green form prefered young leaves and the pink fonn was found on the lower leaves on which they had first infested, and later they are crowded on the newly matured leaves and even on the unfurled leaves. The synthesized results of the progress of the above counts made every other day, in principle, on the cabbage are shown in Fig. 6,in terms of the average number of aphids on the same or different plants at the same time in the greenhouse. In conclusion, the green form prefers the young leaf and the pirik form prefers the old leaf in spite of the same or different plants at same time but they crowded to saturated point on their own leaves then they extend to mature or middle leaves. In the last figure, idealized curves show the relative suitability for colonization by the green (……) and pink (--) forms. The vertical line shows the suitability for aphid infestation (the higher as arrow) and the horizontal line shows the leaf age (the older as arrow). The green form seems to be more specifically adapted than the pihk form at the high temperature but the suitability of low temperature on these aphids is not clear.1. In July of 1956,the 2nd survey of the Muridae on the island of Okushiri off the west-south coast of Hokkaido was done and Rattus

(View PDF for the rest of the abstract.)