Prospective agents for the biological control of Cardiospermum grandiflorum Sw. (Sapindaceae) in South Africa.
Balloon vine, Cardiospermum grandiflorum Sw. (Sapindaceae), originally from South and Central America and now invasive in South Africa, was one of five incipient or 'emerging weeds' targeted for biological control in 2003. In search of potential biological control agents, exploratory surveys were conducted in northern Argentina from 2005 to 2009. The surveys, which included plant species in the genus Cardiospermum and other native Sapindaceae, were aimed at determining the distribution and field host ranges of the natural enemies associated with C. grandiflorum. Eight phytophagous insect and two fungal pathogen species were associated with C. grandiflorum, four of which were introduced into quarantine in South Africa for further host-specificity testing. Based on the nature of the potential agents' damage, field distribution, abundance, field host range and the results of preliminary host-specificity tests, the seed-feeding weevil Cissoanthonomus tuberculipennis Hustache (Coleoptera: Curculionidae) and the fruit-galling midge Contarinia sp. (Diptera: Cecidomyiidae) were deemed to be the most promising insect agents. Also promising was the rust fungus Puccinia arechavaletae Speg. (Fucciniales: Fucciniaceae) which caused severe disease symptoms on South African C. grandiflorum. However, feeding on two congeners of C. grandiflorum, whose exact country of origin is disputed, has limited the number of agents that are suitable for release. To resolve this problem, phylogenetic studies are currently under way to verify the contention that both non-target Cardiospermum species are native to South America and not to Africa. If that proves to be true, then these and other agents would qualify for release against C. grandiflorum in South Africa. Although this is a very recent programme, prospects for success seem good.