Costs of ant attendance for aphids

1. Interactions between aphids and ants are considered to be mutualistic, with both partners benefiting. Costs associated with such interactions are likely to be less obvious, although they can be expected, especially if these associations are facultative.
2. It is demonstrated here that there are costs in several life-history parameters to individual aphids resulting from ant attendance. Over several generations Aphis fabae cirsiiacanthoides feeding on Cirsium arvense , at a range of developmental stages, suffered significant costs when tended by Lasius niger , e.g. in terms of a prolonged developmental time, delayed offspring production, proportionally smaller gonads, fewer well developed embryos and a reduced mean relative growth rate. These effects are similar to those observed when aphids feed on poor quality plants.
3. This is the first indication that there is a cost for aphids associated with ant attendance. The significance of this for the evolution of ant attendance in aphids is discussed.