Leaf size and availability of space to the sycamore aphid Drepanosiphum platanoides.

Sycamore aphids feed on the contents of sieve tubes in leaf veins. The smallest aphids prefer to settle on the minor veins of small leaves, but larger aphids select larger veins. On large leaves, however, even the adult aphids prefer to settle on the minor veins. Aphids feeding on large leaves are unable to reach the deeper sieve tubes in the thicker part of the main veins as their stylets are too short. However, the length of the aphids' stylets cannot account for the absence of aphids from the lateral veins of large leaves or the distribution of the various instars on the veins of small leaves. The preference shown by art aphid for leaf veins of a particular size is probably imposed on the aphids by the structure and physiology of' leaf veins of different sizes. The outcome of this is that only a pan of a leaf is suitable for colonization by aphids. [ABSTRACT FROM AUTHOR]