Mechanisms of recognition and discrimination are essential in determining the outcome of multi-species interactions.  In the classic example of mutualism between ants and Acacia trees, ant colonies fiercely defend Acacia trees in exchange for resources provided by the trees.  However, specialist herbivores can gain access to these resources by avoiding recognition by the ants.  We examined the mechanisms by which a specialist herbivore, Mozena sp. (Hemiptera: Coreidae), is able to parasitize the relationship between Acacia collinsii and Pseudomyrmex spinicola in Palo Verde National Park, Costa Rica.  We tested three non-mutually exclusive hypotheses for how Mozena sp. feeds on A. collinsii while avoiding ant attack; these were behavior, chemical defense, and chemical mimicry.  Field experiments quantified ant responses to Mozena sp. using various treatments that isolated the effects of behavior as well as chemical cues from methathoracic glands and cuticle.

Results/Conclusions

Our results show that chemical cues produced by Mozena sp. in both the metathoracic gland and the cuticle reduce the number of ant attacks, however only cuticular cues appear to be essential in escaping recognition on ant-occupied Acacia trees.  In addition, analyses of cuticular hydrocarbon profiles revealed a close match between Mozena sp. and P. spinicola, suggesting chemical mimicry is the primary mechanism driving this interaction.  The parasitism of an ant-Acacia mutualism by Mozena sp. provides an exemplary system in which to address the importance of chemical mimicry in the evolution and maintenance of mutualistic interactions.