Aphid Feeding by Some Polyphagous Predators in Relation to Aphid Density in Cereal Fields

(1) Samples of aphids and predators were taken from ten spring barley and winter wheat fields between May and September 1972-77. (2) The guts of c. 12 000 predators were dissected and the presence or absence of aphid remains recorded. Sixteen species of Carabidae, three species of Staphylinidae and one species of earwig were shown to have fed on aphids. (3) No overall relationship was found between the amount of feeding and aphid densities in the different years. But, when the species were considered separately, it was found that the proportion containing aphid remains increased with aphid density, though the form of this relationship varied between species. (4) Tachyporus spp. had a limited response to aphid density and Amara plebeja, A. aenea and Notiophilus biguttatus ate aphids only at higher aphid densities. Forficula auricularia, Agonum dorsale and Demetrias atricapillus were the most important, both in terms of the overall percentage containing aphid remains, and the predation index (proportion containing aphid remains during the aphid increase phase multiplied by the mean density of the predator at this time). These three species should be the most valuable in restricting build up of aphids. (5) Successful aphid predation at low aphid density may be partly related to the climbing ability of the predator.