The benefits and risks of biological control in Africa

Abstract: Biological control using host-specific natural enemies has been used as a
management tool for invasive alien plant species and crop pests in Africa dating back to the
1700s. South Africa was the first country to deliberately introduce a weed biocontrol agent for
an invasive alien weed (Dactylopius ceylonicus on Opuntia monacantha in 1913). In the late
1940s, Cordia curassavica was successfully controlled in Mauritius, while in 1953, biological
control was initiated against Lantana camara in Kenya. Several species of aquatic weeds were successfully targeted across Africa, starting in 1969 with Salvinia molesta in Zimbabwe, and in 1990s, with regional projects on Pontederia crassipes and Pistia stratiotes. 141 species of biological control agents have contributed to the control of 69 weed species in 30 countries. The risks of classical biological control are low with no sustained non-target impacts being recorded in Africa, whilst benefits are high with benefit:cost ratios ranging from 15:1 to 4333:1. The biological control of arthropod pests in Africa was initiated in 1762 with the ill-advised introduction of Indian Myna birds into Mauritius for the control red locust. 404 species of biological control agent have been released against 119 target pests. The most notable projects have been the biological control of mango mealybug that resulted in a benefit:cost ratio of 808:1 and cassava mealybug 740:1. The benefits of biological control to Africa have been high with low risk. The increasing number of weeds and crop pests coupled with pressure to reduce reliance on pesticides bodes well for classical biological control on the continent.