Ant defence of a dioecious shrub, Adriana quadripartita (Euphorbiaceae), with extrafloral nectaries

Extrafloral nectaries (EFNs) can function to indirectly reduce herbivory by attracting ants that interfere with or predate on herbivorous insects. So as to examine the efficacy of ants as defenders of plants with extrafloral nectaries (EFNs) against herbivores, an ant-exclusion experiment was conducted on plants of the dioecious species Adriana quadripartita (Euphorbiaceae). The experiment was conducted on Torrens Island, South Australia, and adds to previous work that examined the associations among adrianas, ants and invertebrate herbivores at several locations across Australia. The aim of the present study was to investigate whether ants that tend EFNs reduce herbivore numbers and levels of herbivory, and whether this ant–plant–herbivore interaction differs between male and female A. quadripartita plants. The abundances of ants and invertebrate herbivores were overall greater on male than on female plants. The exclusion of ants from branches resulted in an increase in herbivore abundance on male and female plants; however, ant exclusion resulted in an increase of foliar damage on male plants only. Whereas previous research on A. tomentosa shows that ants can decrease herbivore abundance, the results here provide the first evidence that EFNs on adrianas can function to decrease foliar herbivory.