Can artificial nectaries outcompete aphids in ant-aphid mutualism? Applying artificial sugar sources for ants to support better biological control of rosy apple aphid, Dysaphis plantaginea Passerini in apple orchards

Abstract

The rosy apple aphid, Dysaphis plantaginea Passerini, is a serious pest in apple orchards. It establishes close facultative mutualistic relationships with ants. An experiment manipulating the presence of the common black ant, Lasius niger (L.), in colonies of D. plantaginea in the canopy of apple trees by provision of ant-feeders (artificial nectaries) containing sucrose solution as an alternative sugar source were conducted in apple orchards in the United Kingdom and Hungary to test if this method can regulate densities of D. plantaginea below the threshold for economic damage through enhancing the activity of its natural enemies. Apple trees with physical ant-exclusion (sticky barriers) and without any treatment were used as controls.Ant-feeding with sucrose solution, in a similar way to physical ant exclusion, effectively reduced the numbers of ants tending D. plantaginea colonies and it consequently resulted in a reduction in D. plantaginea populations in both studies. In spite of marked differences in natural enemy abundance and composition found in UK and Hungary, both treatments caused significant increases in natural enemy (e.g. Dermaptera, Heteroptera, Coccinellidae, Syrphidae) pressure on D. plantaginea. Our results show that supplementary sugar feeding of ants is a successful method for supporting biocontrol of rosy apple aphid through enhancing the effectiveness of its natural enemies. This new biocontrol approach to control aphids in apple orchards is likely to substantially reduce the need for aphicide sprays in orchards and is compatible with organic pest control. The implications of these results for supporting better biological control of aphids in apple orchards are discussed.