Background/Question/MethodsAt virtually any stage in their lifecycle, plants are susceptible to herbivory. Insect herbivores thus play a significant role in the survival and reproduction of plants. Because herbivory is costly, selection has favored the development of defenses. One such defense is the deployment of extrafloral nectaries to attract and reward natural enemies of plant herbivores. Although it has been suggested that the attraction of ants to extrafloral nectaries in Erythrina flabelliformis has evolved to inhibit herbivory, this relationship has not been demonstrated. The focus of this project was to determine 1) how patterns of nectar secretion and ant visitation changed within a 24 hour cycle 2) whether herbivory increased in the absence of ants 3) whether ants present on extrafloral nectaries provided effective defense 4) how these characteristics vared among populations. We documented daily patterns in nectar secretion and ant visitation, and performed a series of ant-exclusion and herbivore-addition experiments.

Results/Conclusions Our data suggest that some ant species responded aggressively to potential caterpillar herbivores. In populations where these ant species are dominant visitors to extrafloral nectaries, ants inhibit caterpillar herbivory on flowers and fruits. In addition, nectary size between populations appears to be related to the number of defensive ants attending nectaries. These results suggest an evolved nectar-mediated defense mutualism in which Erythrina flabelliformis is defended against caterpillar herbivory by certain ant species.