Prospects for the biological control of northern temperate weeds in South Africa

The Northern Temperate Weeds programme is a novel biological control (biocontrol) programme started in 2017, with the aim of reducing the impacts of northern temperate weeds that are common, widespread and problematic in the high elevation grasslands of South Africa. As these regions are the most important systems for water security, providing nearly 50% of all water run-off, it is surprising that these species were not targeted for biocontrol previously. Thus far, research has focused on biocontrol feasibility as well as ecological and socio-economic impact studies on several northern temperate weeds, including Pyracantha angustifolia (Franch.) C.K.Schneid, Rosa rubiginosa L., Cotoneaster spp., Rubus spp., (all Rosaceae) and Salix spp. (Salicaceae). In addition, research conducted in the USA and Europe on the natural enemies associated with two of these species, Robinia pseudoacacia L. and Gleditsia triacanthos L. (both Fabaceae and native to the USA), have provided South African researchers with the necessary foundation to initiate programmes against these weeds. Research in South Africa is currently focused on pre-release studies on R. pseudoacacia, using the leaf miner Odontota dorsalis Thunberg (Coleoptera: Chrysomelidae) and the black locust midge Obolodiplosis robiniae Haldeman (Diptera: Cecidomyiidae), and on G. triacanthos, using a seed bruchid, Amblycerus robiniae F. (Coleoptera: Chrysomelidae). Progress with these programmes and potential constraints that may limit success, are discussed.