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). Jpn. J. Appl. Ent. Zool. 32: 169-175 (1988) The maple aphid (Periphyllus californiensis) infests maple trees the whole year round, and it spends the summer as aestivating dimorph, a first instar larva morphologically different from the normal larva. The reproduction of maple aphid in spring was investigated in relation to food resources. Maple aphids produced normal larvae on unexpanded leaves and aestivating dimorphs on expanded leaves. Even after they had produced aestivating dimorphs, they produced normal larvae when transplanted onto unexpanded leaves. Expanded maple leaves were nutritionally poor and the aphids reared on them produced only a few larvae. Unexpanded leaves showed high soluble nitrogen contents which decreased rapidly as the leaves expanded. Reproduction of aestivating dimorphs seemed to be correlated to the low soluble nitrogen contents in leaves. In a tree, inflorescences or new leaves, which were located in the terminal part of shoots contained higher amounts of soluble nitrogen and were suitable for the reproduction of the aphids. However such good feeding sites disappeared rapidly with time. Therefore, the migration of alates in the second generation to late budding trees was considered to be an efficient mechanism to secure food.

The maple aphid infests maple trees the whole year round, but in spring its feeding site is restricted to buds, growing shoots and inflorescences. Some differences in the time of budding and the number of inflorescences are found among maple trees, and the favourable feeding site of the aphid distributes contagiously both in time and space. Early budding contributes to lower the mortality of fundatrices, but late budding prepares suitable feeding site for winged aphids in the second generation. Each winged aphid can produce either larvae or aestivating dimorphs depending upon the host tree condition. Dispersal of winged females and their ability in producing both larvae and aestivating dimorphs contribute to exploit the feeding site efficiently. Zusammenfassung Zur Wirkung von Knospung und Blüte der Ahornbäume auf die Populationsentwicklung der Ahorn‐Blattlaus, Periphyllus californiensis Shinji (Hom., Aphididae) P. californiensis befällt die Ahornbäume während des ganzen Jahres, saugt jedoch im Frühjahr nur an Knospen und Blüten. Es wurden individuelle Unterschiede im Knospen und Blühen der Bäume festgestellt. Das Saugen breitet sich dann räumlich und zeitlich schädlich aus. Ein frühes Austreiben der Knospen trägt dazu bei, die Sterblichkeit der Fundatrices zu verringern, während spätes Austreiben geeignete Saugstellen für die geflügelten Tiere der 2. Generation schafft. Jede geflügelte Blattlaus kann — in Abhängigkeit von den Wirtsbaumbedingungen — entweder Larven oder überwinternde Dimorphen hervorbringen. Diese Fähigkeit, in Verbindung mit der Ausbreitung der geflügelten Weibchen, ermöglicht es der Population, die Saugstellen effizient auszunutzen.

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