Do Lasius niger ants punish low-quality black bean aphid mutualists?

► Aphis fabae clones vary in producing a key sugar attractive to ants: melezitose. ► We investigate whether ants 'punish' melezitose-deficient clones. ► Ants are shown to visit low- and high- melezitose secreting clones equally. ► Hence, active partner sanctioning is absent in this mutualism. ► Even so, ants more likely collected honeydew from high-melezitose secreting clones.