following spring.

The within-year dynamics of aphids are largely determined by seasonal changesin host quality. Aphids do best when amino acids are actively translocated in thephloem. In spring, the leaves grow and import amino acids via the phloem; in summer leaves are mature and export mainly sugars. In autumn, the leaves senesce andexport amino acids and other nutrients. Thus on trees the leaves are most suitablefor aphids in spring and autumn. The differences in within-year population dynamics of aphids are due to differences in the