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It is now well established that ants living on plants deter herbivores, reduce herbivory, and increase plant reproduction. Although ants reduce herbivore abundance through density-mediated effects, few consider the importance of trait-mediated effects within these interactions. The pheromone avoidance hypothesis suggests herbivores avoid confrontation with ants by eavesdropping on ant chemical communication. Here I tested if an herbivorous beetle avoids the leaves of a tropical tree when marked by the semiochemicals of two ant species (Azteca instabilis and Camponotus textor) and if that avoidance resulted in lower damage to leaves. I performed beetle choice tests with leaf pairs from Conostegia xalapensis. I allowed ant workers (A. instabilis or C. textor) to patrol the ant-treated leaf prior to the experiment (for 0, 5, 30, 90, or 180 minutes) and left the control leaf unexposed to ants before comparing herbivore choice between the two leaves. Additionally, I compared herbivore choice between leaves from trees with and without A. instabilis.
Results/Conclusions
The number of herbivores on control leaves (un-exposed leaves) was 2.8 and 1.6 times higher than on leaves previously patrolled by A. instabilis and C. textor, respectively. Control leaves were also 3.9 and 1.8 times more damaged than A. instabilis and C. textor treated leaves, respectively. Increasing the amount of time an ant-treated leaf was exposed to A. instabilis resulted in a non-linear increase in herbivore preference for control leaves relative to ant-treated leaves. Finally, leaves from trees without A. instabilis had 1.9 times more herbivores present and were 2.1 times more damaged than leaves from trees with A. instabilis nests after the conclusion of the choice experiments. These findings suggest that herbivore avoidance of ant semiochemicals exists for two ant species within two broadly distributed and ecologically important ant genera. It also provides an example of the importance of trait-mediated effects driven by olfactory cues in a terrestrial species interaction.
