Sugar feeding of the common black ant, Lasius niger (L.), as a possible indirect method for reducing aphid populations on apple by disturbing ant-aphid mutualism

[Display omitted] ► Common black ants (Lasius niger) tend and protect the apple pest aphids Dysaphis plantaginea and Aphis pomi. ► Ant exclusion with sticky barrier or supplementary honey feeding significantly reduces ant attendance. ► Reduced ant attendance results in higher activity of aphidophagous predators and lower aphid infestation on apple trees. The rosy apple aphid, Dysaphis plantaginea Passerini, and the green apple aphid, Aphis pomi De Geer, are serious pests of apple and are commonly found together as pests in apple orchards. Both species establish mutualistic relationships with ants. Two experiments manipulating the presence of the common black ant, Lasius niger (L.), visiting aphid colonies by ant-exclusion with sticky barriers, or ant-feeding with honey as an alternative sugar source, were conducted, one in an apple orchard in the United Kingdom and one in an apple orchard in Hungary to test if these methods can reduce aphid infestations on apple trees. The exclusion of ants reduced D. plantaginea and A. pomi populations in both experiments. It caused significant increases in natural enemy pressure on both aphid species in the experiment in the UK and on A. pomi in the experiment in Hungary. Ant-feeding with honey reduced the numbers of ants tending D. plantaginea colonies, and it consequently resulted in a reduction in D. plantaginea populations in both experiments. The supplementary feeding of ants was more effective in reducing D. plantaginea than A. pomi. This was probably due to the greater intensity of ant attendance on A. pomi than on D. plantaginea colonies when both species were present together. Our results showed that supplementary sugar feeding of ants is a successful method for supporting biocontrol of apple aphids through enhancing the effectiveness of their natural enemies. However, the species of aphid targeted and the design and position of the feeder could affect the efficacy of this biocontrol method.