An experimental field study of different levels of insect herbivory induced by Formica rufa predation on sycamore (Acer pseudoplatanus). II. Aphidoidea.
As part of a wider study of the effect of insect herbivory on sycamore (Acer pseudoplatanus) trees, the population dynamics and feeding of 2 aphid species, Drepanosiphum platanoidis and Periphyllus testudinaceus, were studied in a mixed deciduous woodland in North Lancashire, UK. Higher and lower densities and feeding activity of the aphids were caused by the foraging activity of Formica rufa, which was experimentally manipulated using grease bands on the tree trunks. The ant is a predator of D. platanoidis but tends P. testudinaceus colonies. Sap removal from the trees was calculated from numbers and age classes of the 2 aphids and measurements of excretory rates of the instars at different temperatures in laboratory and field. In the case of D. platanoidis, this was done directly by catching honeydew droplets as they were produced, but for P. testudinaceus it was necessary to measure the quantity of honeydew ingested by the attendant F. rufa. Approximately 3 times as much sap (250-600 mg dry weight/shoot p.a.) was removed by D. platanoidis from ant-free trees as from ant-foraged ones. P. testudinaceus removed approximately 50 times as much sap (20-150 mg dry weight/shoot p.a.) from foraged as from unforaged trees.