Defining Quality in a Wood Ant - Aphid - Tree Foraging Network

Quality distance trade-offs shape foraging dynamics, but defining quality can be complex. Ants ‘farm’ aphids to collect honeydew, a significant food source for Formica lugubris wood ant colonies. Previous modelling and empirical data indicate that ant colonies do not invest equally in all trees where honeydew is foraged: they treat different trees and their associated aphid populations as being higher or lower value food sources. Honeydew composition varies based on tree and aphid species. Ants could be looking for specific sugars, amino acids, plant defence compounds, or other components of aphid honeydew. Using worker investment as an indicator of a site’s value to the colony, we aim to define “quality” based on the chemical composition of the food retrieved. We collected samples from trees (phloem), aphids (material), and ants (crop contents) on low and high investment sites. Through metabolomic analysis, we investigated the metabolites flowing over the tree-aphid-ant processing pipeline and the final composition of crop contents. We found distinct metabolomic profiles of low and high investment sites in all three sample types (Phloem Sap, Aphid Material, and Crop Contents). Our results provide the first data about what components of the resources provided by trees are treated by ants as high quality, and suggest future work to further elucidate this line of inquiry into resource use by Red Wood Ants.