Selective predation by ants against less-honeydew secreting aphids

Many ant-aphid interactions illustrate the concept of a mutually beneficial association between two organisms: aphids provide ants with honeydew; in return, ants defend aphids from enemies. However, ants also often prey on the aphids they attend, and we do not know if the predation pressure causes any adaptations on the side of aphids. The aphid Stomaphis japonica has an obligate mutualistic association with Lasius ants. Here, we report evidence of selective predation of less-honeydew secreting Stomaphis aphids by the tending Lasius ants. We show that 1. the aphids are severely preyed on by the ants - up to half of the aphids standing population per day. 2. the ants selectively prey on the aphids which do not deliver honeydew when attacked, and 3. the frequency of aphids honeydew secretion is heritable. These results suggest selective predation by ants against less-honeydew secreting aphids takes place and it is heritable.