Providing sugar sources for ants improves the biological control of Aphis spp. in apple orchards

Abstract

The green apple aphids Aphis pomi DeGeer and A. spiraecola Patch are serious pests of apple, especially in young orchards, where both species establish facultative mutualisms with ants. This study, conducted in Hungary in 2014 and 2015, manipulated the presence of the common black ant Lasius niger (L.) on colonies of Aphis spp. in apple tree canopies. To this end, two kinds of sugar dispensers (bottle dispensers and agar jelly cubes), each providing a sucrose solution with 300 g/1000 ml concentration, were deployed as alternative sugar sources for the ants, with plots lacking dispensers serving as controls. Both forms of sugar provisioning reduced the number of ants tending Aphis spp. colonies and reduced aphid populations compared to controls in both years. However, bottle dispensers demonstrated consistent efficacy in both years, whereas agar jelly cubes were less reliable in distracting the ants. Both treatments significantly increased the abundance of natural enemies at Aphis spp. colonies compared to controls. Our results indicate that the provisioning of ants with sugar in apple orchards can effectively disrupt ant-aphid mutualisms in the case of Aphis spp., by drawing ants away from aphid colonies and thus increasing natural enemy predation on aphid colonies. The use of sugar-feeding tactics to alter ant behaviour should permit reduced pesticide use in apple orchards, whether to control aphids or other pests that might serve as prey for ants, and is fundamentally compatible with biological pest control in apple orchards.