Urban Lasius niger ants more readily accept low concentration sucrose solution than rural ants

Urbanisation causes broad changes in biotic and abiotic factors, which are often detrimental to animals. While extensive attention has been focussed on food resources for pollinators, comparatively little research has examined resources for aphidophagous insects. Many ants, such as Lasius niger, are highly aphidophagous, relying on honeydew secretions for the majority of their carbohydrate intake. Ants will also often reject sugar solution which is of lower concentration than that they were expecting. Here, we ask whether Lasius niger ants from urban environments show differential acceptance to various sucrose solution molarities. We offered outgoing ants on active foraging trails drops of sucrose solutions over a range of molarities (0.125, 0.25, 0.5, 1, and 2M), and quantified acceptance. Acceptance was scored using a simple behavioural measure of whether the ant remained in contact with the sucrose drop for over 3 seconds (full acceptance), broke away from the drop within 3 seconds but remained in the area and eventually drank to satiation (partial acceptance), or did not drink to satiation and walked away (rejection). Urban ants showed a significantly higher acceptance of all sucrose molarities than rural ants, with this difference especially pronounced at lower molarities. This may indicate that they are under nutritional stress for carbohydrates. Ant responses to sucrose solutions may allow a straightforward measure of the availability of carbohydrate resources in the environment.