Phoretic association of blackflies (Oiptera: Simuliidae) with heptageniid mayflies (Ephemeroptera: Heptageniidae) in South Africa : short communication

The phoretic or epizoitic association of blackfly (Diptera: Simuliidae) larvae and pupae with other aquatic arthropods has been documented for a number of tropical African species (Grenier & Mouchet 1959; Corbet 1961, 1962; Germain et al. 1966; Disney 1969, 1971a–d, 1973; also references in Crosskey 1990). The significance of these associations has led to much speculation, although no scientific conclusions regarding the origin and purposes of the associations have been reached (Corbet 1961; Crosskey 1990). Attachment of simuliid larvae and pupae to other aquatic arthropods could be fortuitous, especially where dense populations of simuliid larvae occur, and where they may encounter difficulties in locating suitable substrates on which to attach. There are, however, a number of blackfly species that have developed obligatory associations with specific arthropod hosts and these simuliids manifest a range of unique morphological adaptations. In the larvae, these include a modified abdominal cuticle, structurally modified or reduced cephalic feeding fans, the ventral position of the terminal abdominal proleg with its attachment hooks and, in the pupae, the development of additional abdominal hooks that secure them in their reduced ‘half slipper-shaped cocoon’ (Crosskey 1990). The distribution of obligate phoretic associations between blackflies and other arthropods is recorded as being restricted to central Asia and tropical Africa. In central Asia only mayflies of the family Heptageniidae (Ephemeroptera) are involved in the association, and the blackfly larvae and pupae do not manifest any striking morphological adaptations. In tropical Africa there are phoretic associations of blackflies with Decapoda (Potamonautidae and Atyidae) and Ephemeroptera (Heptageniidae, Oligoneuriidae and Baetidae). These obligatory phoretic blackfly larvae and pupae have many specialized morphological modifications. In Africa the most widespread records of phoretic associations are those between Simuliidae and Potamonautidae. These extend from Liberia and Kenya to Malawi (Crosskey 1990). The association between Simuliidae and Ephemeroptera range from Liberia and Uganda to Tanzania and southern Democratic Republic of the Congo, with a recent record in northern Namibia (Palmer & de Moor 1998). Surveys conducted by staff of the Albany Museum in 1990 and 1991 recorded larvae and pupae of Simulium (Phoretomyia) lumbwanum de Meillon together with large numbers of nymphs of heptageniid mayflies belonging to Afronurus scotti Schoonbee and a Compsoneuria species. One mature nymph of Compsoneuria supported a penultimate instar larva of S. lumbwanum (Figs 1, 2). The specific identification of the Compsoneuria nymph could not be confirmed as several nymphs of known African species have not yet been de-