Effects of the landscape context on aphid-ant-predator interactions on cherry trees

Abstract

The loss and isolation of semi-natural habitats reduces biodiversity in agricultural landscapes, with potential negative consequences for the biological control of pest insects. We investigated effects of the landscape context on interactions between the black cherry aphid Myzus cerasi, ants, and aphid predators on young cherry trees. Thirty study sites varied independently in their amount of woody habitat in a 500 m radius and their isolation from woody habitats. We infested young cherry trees with aphids and applied glue rings to half of the trees to exclude ants and earwigs. Early-season densities of syrphids and coccinellids were reduced by ants, and cumulative aphid densities were 10 times higher on ant-accessed trees than on trees from which ants were excluded. Densities of earwigs and syrphids were significantly lower on trees isolated from woody habitats than on trees adjacent to forest. Cumulative aphid densities were two times higher on trees isolated from forest, but only in the absence of glue rings, suggesting that differences in earwig densities could have caused this pattern. Neither predator densities nor aphid densities were influenced by the amount of woody or open semi-natural habitat in a 500 m radius. Growth of cherry trees was reduced by aphids. We conclude that the mutualistic interaction between aphids and ants was largely independent of the landscape context. By contrast, the ecosystem service of aphid suppression was reduced by habitat isolation.