Honeydew flicking by treehoppers provides cues to potential tending ants

The honeydew-producing treehopper, Guayaquila xiphias, is frequently tended by ants on shrubs of Didymopanax vinosum in the Brazilian savannah. Field experiments showed that the flicking of accumulated honeydew by untended treehoppers provides cues to ground-dwelling ants. Upon finding scattered honeydew droplets on the ground, the ants climb onto the host plant and start tending activity. Honeydew-soaked filter papers placed beneath unoccupied host plants induced significantly more ants to climb onto the plant than water-soaked papers. Because predation and parasitism on G. xiphias can be severe at early stages, and tending ants protect the homopterans against predators and parasitoids, the capacity to attract ants early in life can be crucial for treehopper survival. ? 1996 The Association for the Study of Animal Behaviour Phloem-feeding Homoptera (primarily aphids, membracids and scales) are commonly tended by ants that harvest their energy-rich honeydew (Auclair 1963; Way 1963). Homopteran honeydew is generally regarded as an ant attractant (Sudd 1987), and tending ants can provide a range of benefits to homopterans, including protection from natural enemies (Buckley 1987a, b, and citations therein). Ant colonies may simultaneously tend many homopteran aggregations, and intraand interspecific competition for the services of ants can adversely affect homopteran fitness through reduced tending levels (Cushman & Addicott 1989; Cushman & Whitham 1991). Predation pressure on homopteran aggregations can be severe at early developmental stages, and ant tending can greatly increase the number of surviving nymphs (Bristow 1983; Cushman & Whitham 1989). Therefore, the capacity to attract ants early in life can be crucial for the survival of ant-tended homopterans, especially under low ant densities (Cushman & Addicott 1989). When untended by ants, many homopterans flick away the accumulated honeydew either with the hind legs or caudae or by contracting the rectum or entire abdomen (Hölldobler & Wilson 1990). The flicking of accumulated honeydew may reduce fungal attack to the homopterans and adjacent plant parts (Beattie 1985; Buckley 1987a, b, and citations therein). The honeydew-producing treehopper, Guayaquila xiphias (Membracidae), is frequently tended by ants in the cerrado woodland of Brazil. Del-Claro (1995) identified 21 ant species tending G. xiphias aggregations, and used ant-exclusion field experiments to show that tending ants protect homopteran nymphs from predators such as salticid spiders and syrphid flies, and egg masses from parasitoid wasps. We have suggested (DelClaro & Oliveira 1993) that honeydew droplets that fall on lower leaves and ground from G. xiphias aggregations could serve as cues to potential tending ants. This behaviour pattern would be particularly important for the survival of developing brood by minimizing mortality due to predation and parasitism at early stages (DelClaro 1995). In the present paper we tested whether honeydew flicking by nymphs of G. xiphias increased the probability that grounddwelling ants climbed onto the host plant and tended the treehoppers.