Ants Protect Tropical Homoptera Against Nocturnal Spider Predation

Abstract

Three species of sap-sucking eurymelid bugs, including the economically significant Ipoides melaleucae Evans, form nymphal aggregations tended by ants, Iridomyrmex spp., on saplings of Eucalyptus camaldulensis and Melaleuca viridiflora in tropical northwestern Australia. Experimental exclusion of the ants increased bug mortality rates significantly (P < 0.01), by a factor of approximately 2.5. The increased mortality occurred almost entirely at night: nocturnal mortality rates increased 3-4 times (P < 0.01), whereas diurnal mortality did not increase significantly. Mortality was apparently due to nocturnal predation by small spiders rather than attack by parasitoid wasps or predatory insects. This is the first study to distinguish the effects of diurnal and nocturnal suites of predators and parasitoids on ant-tended Homoptera. It suggests that the role of nocturnal interactions may have been underestimated, at least for tropical Homoptera. MANY SAP-SUCKING BUGS are tended by ants which consume their sugary faecal exudates and protect them against their predators, parasitoids and pathogens. Besides their theoretical interest to evolutionary ecologists, these interactions are of considerable practical and economic significance in pest management, since many of the worst viral and bacterial diseases of crop plants are transmitted by Homoptera. The significance of ant protection has been demonstrated experimentally for a number of ant-tended Homoptera. For some (typically sedentary) species the main effect of the ants is to reduce mold infestation by removing honeydew (Majer 1982). More commonly, the ants actively protect the bugs against