A meta-analysis of factors associated with the intensity of ant-honeydew producing insect interactions.

Mutualisms between species are incredibly widespread, and those between ants and honeydew producing insects (HPIs) are one of the most common mutualisms found in terrestrial ecosystems. HPIs, such as aphids, feed on phloem, a vascular plant tissue that is high in sugars, but low in amino acids. In order to obtain the nutrients from phloem that they need to survive, HPIs must dispose of the excess sugars in the form of honeydew. Sugars are a vitally important carbohydrate source for ants, so many species of ants and HPIs have evolved mutualisms in which ants consume honeydew in exchange for protection from predators. Meta-analysis techniques were used to assess published studies to determine taxonomic distribution of these interactions and the extent to which this relationship is beneficial to both insect groups.  Net benefit to the ants is quantified by ant abundance, honeydew consumption, as well as the costs associated with maintaining HPI colonies. The hemipteran colony sizes, protection from parasitism, and reduced resource competition are used as measures for hemipteran benefit in conjunction with the associated costs of being tended such as increased honeydew production. This study provides insight into why these interactions are so ubiquitous worldwide.