BODY-SIZE DISTRIBUTION IN APHIDS - RELATIVE SURFACE-AREA OF SPECIFIC PLANT STRUCTURES

1. The distribution of the body sizes of British aphids is right-skewed on a logarithmic axis, as in other taxa, Over the size range 2-5mm there is a marked decrease in numbers of species with increase in size, which on a log log scale has an exponent of -3, The exponent for the right-hand side of the size distribution of British plants is -0.7. 2. The sizes of sixty-eight species of the genus Aphis are weakly correlated with the size of their respective host plants. 3. An aphid's size is strongly correlated with the length of its proboscis, which indicates the depth to which it has to probe plant tissues in order to feed. 4. On average, trees host more species of aphids than either shrubs or herbaceous plants, which appears to be associated with the relative surface area of specific plant structures. The surface area of plants is mainly made of leaves and most species of aphids are leaf feeders. The largest and least numerous species of aphids feed on the branches and trunks of trees, the proportional cover of which is less than that of leaves. 5. Taking into account all the above observations, a functional explanation in terms of the relative surface area of specific plant structures is offered to account for the size diversity curve of aphids.