Biological control of jointed cactus, Opuntia aurantiaca (Cactaceae), in South Africa

Abstract

Jointed cactus, Opuntia aurantiaca Lindley, has been a problem weed in South Africa for nearly a century. Its taxonomic status, history of introduction, and chemical and biological control were reviewed in 1979. The present account updates this information and deals with recent South African research on the ecology of O. aurantiaca and its biological control agents, and on the management of the weed. This review places some emphasis on the primary agent, the cochineal insect Dactylopius austrinus De Lotto (Homoptera: Dactylopiidae), with a shorter commentary on the phycitid moth Cactoblastis cactorum (Bergroth) that has also become established on jointed cactus. Research on three other introduced moths, Tucumania tapiacola Dyar (Phycitidae), Mimorista pulchellalis Dyar (Pyraustidae) and Nanaia sp. Heinrich (Phycitidae), is abstracted. Of the latter three species, only M. pulchellalis has become established, but its role in biological control is insignificant. It is concluded that: (i) the utility of insects as biological agents against jointed cactus has probably been fully exploited; (ii) the importance and threat of O. aurantiaca as a weed in South Africa may have been overestimated; (iii) future research emphases should be on the role of pathogens as biocontrol agents and on the formulation of area-specific integrated management procedures involving D. austrinus and herbicides.