Adaptation to new resources: interaction between introduced psyllids and native and exotic ants in Eucalyptus plantations in NW Spain

The multiple uses of eucalypt wood have driven massive plantations around the world. These plantations have been progressively invaded by Australian insects, some of which have become pests, threatening the plantation productivity, and modifying ecological networks of trophic interactions. In this study we addressed whether ants could recognize and exploit the food sources offered by the introduced psyllids (Sternorrhyncha) associated with eucalypts. We hypothesised that ant-psyllids interaction will be more likely with exotic ant species than with the native ones, because of their higher abundance in anthropogenic habitats. For this reason, we also expected differences in ant biodiversity between plantations located near and far from human settlements. We studied the presence of ants on eucalypt trees, the ant diversity found on the ground in eight eucalypt plantations, and analysed in the laboratory the interactions between psyllids and three ant species, two native and one invasive. In the field, we found native ant species over psyllid clusters in eucalypts, as well as a higher use of eucalypt resources and colonization by specialist species in plantations distant from human settlements. However, we did not find differences in ant diversity between plantations near and distant from human settlements. Despite their absence in the field, during the laboratory experiment, exotic ant workers were more attracted to psyllids than the native ants. Our results point to invasive species as potential users of this resource. We discuss potential factors involved in the ant-psyllid interactions and suggest that introduced eucalypt plantations are low-quality habitats for ants.