An experimental field study of different levels of insect herbivory induced by Formica rufa predation on sycamore (Acer pseudoplatanus). I. Lepidoptera larvae.
Lepidoptera populations and feeding damage were measured on ant-foraged and ant-free sycamore (Acer pseudoplatanus) trees in North Lancashire, UK. Caterpillar populations were 3 - 4 times as abundant on unforaged trees as on foraged ones. Trees banded with grease to reduce foraging by Formica rufa had caterpillar densities intermediate between naturally foraged and unforaged trees. The species composition of the Lepidoptera community was altered by F. rufa foraging. A higher proportion of larvae of Operophtera brumata escaped predation than larvae of other species. Leaf damage due to caterpillars was measured in the field and also calculated from the results of laboratory feeding experiments on 4 common species, and applied to field measures of population density and weight classes. Direct field measurements showed that unforaged trees suffered approximately 5% loss of leaf area from caterpillar consumption, whereas foraged trees suffered 1% damage. Banded trees were in the middle of this range. Indirect estimates from feeding experiments of expected damage showed broad agreement with the direct measurements.