Cordia alliodora photos by Elizabeth Pringle

ACG researcher Elizabeth Pringle has had her photographs of Cordia alliodora and its associated insects featured in the Bulletin of the Ecological Society of America.

The Neotropical tree Cordia alliodora produces hollow stem nodes that Azteca ant colonies use as housing. These ants patrol and defend the tree from leaf-eating herbivores. Ants also tend tree-sap-feeding scale insects inside stem nodes, and these scale insects produce sugar-rich excretions that ants consume. Experiments and observations showed that: larger ant colonies were associated with more scale insects and were better leaf defenders than smaller colonies; individual ants that ate more sugar were more aggressive defenders; and scale insects were more numerous in the trees’ young tissues, which appeared to stimulate better ant defense of young leaves. These findings suggest that although scale insects are herbivores and therefore potentially costly to trees, they also indirectly benefit trees by increasing the effectiveness of ant leaf defense. These indirect benefits point to positive feedback between tree investments and ant services, which may stabilize ant–tree mutualisms in evolutionary time.

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