Aggregation in the lime aphid (Eucallipterus tiliae L.) : 1. Leaf vein selection and its effect on distribution on the leaf.

Lime aphids feed on the contents of sieve tubes in the leaf veins. Aphids on the undersides of large leaves tend to select the smallest veins, while those on small leaves tend to select the larger veins. This tendency increases with the size of the aphid. Since only 4% of the total leaf area is covered by the larger veins, crowding is imposed on those aphids feeding from them. In spring, when the leaves are young and small, close spacing of the aphids results due to their tendency to select large veins. In summer, when the leaves are mature and large, wider spacing between aphids occurs due to their tendency to occupy more of the leaf surface.