Biological Control ofSolanum mauritianumScop. (Solanaceae) in South Africa: Will Perseverance Pay off?

Abstract

Solanum mauritianum Scop. (Solanaceae), a fast-growing tree with a high reproductive capacity, threatens several commercial activities and natural habitats in the higher rainfall regions of South Africa. Biological control efforts spanning 26 years have previously been confined to South Africa, but have recently been extended to New Zealand. The weed is a particularly challenging target for biological control, largely because of its taxonomic relatedness to economically important and native plant species which resulted in the rejection or shelving of the majority of candidate agents tested thus far. Despite these problems, two insect agents, the sap-sucking Gargaphia decoris Drake (Hemiptera: Tingidae) and flowerbud-feeding Anthonomus santacruzi Hustache (Coleoptera: Curculionidae), have been released in South Africa. Gargaphia decoris was first released in 1999 and has become established in several regions of the country. Although large outbreaks and extensive damage have been observed in the field, to date these have been erratic and insufficient to inflict meaningful damage on the weed populations. Anthonomus santacruzi was released in early 2009 and so far appears to have established at two sites in KwaZulu-Natal. This paper is a review of the biological control programme against S. mauritianum in South Africa, including (i) aspects of the weed that are pertinent to its invasiveness and management, (ii) the current status of the two prominent insect agents, and (iii) the direction of future research efforts.