Biological control of invasive alien plants in South Africa: necessity, circumspection, and success

The negative impacts of invasive alien plants on the biodiversity, water supplies, and economy of South Africa are severe. Thousands of people are employed to clear the landscape of these invasive alien species, particularly trees, from conservation and riparian areas. The long-term suppression of the most virulent invasive plants in South Africa will never be possible without the intervention of biological control. Furthermore, the use of specially selected and carefully tested plant-feeding insects, mites, and pathogens as biological control agents is very safe, albeit never completely risk free. We present examples and data from South Africa to support these assertions and to show that biological control is often extremely successful and highly cost effective.