Biological control of silverleaf nightshade, Solanum elaegnifolium, and bugweed, Solanum mauritianum, (Solanaceae) in South Africa

Abstract

The weed status and biological control of two introduced solanaceous plant species in South Africa are reviewed. Solanum elaeagnifolium Cav. (silverleaf nightshade, satansbos), indigenous to the southern USA, Mexico and Argentina, is a weed of arable and pastoral land. Mechanical adn herbicidal attempts at control have been largely unsuccessful. Faunistic surveys in the countries of origin of S. elaeagnifolium revealed at least 15 potential biocontrol agents, of which only a fruit-boring gelechiid moth, Frumenta nephelomicta (Meyrick), has so far been released, but failed to establish. Solanum mauritianum Scop. (bugweed, bugtree), indigenous to Argentina, Brazil and Uruguay, is a weed mainly of commercial forests in the high-rainfall areas of South Africa. The search for potential biocontrol agents has been hampered because the taxonomic status of S. mauritianum is unclear and only three insect species have been introduced into quarantine. Biocontrol of both Solanum weeds has been hindered by the oligophagous habits of the herbivorous species tested so far. The problem is compounded by the large number of agronomic species in the Solanaceae. In particular, Solanum melongena L. (eggplant) is acceptable to most solanaceous folivorous agents, at least under cage conditions, and only the more specialized, endophagous herbivore species may be suitable for introduction into South Africa. However, evidence is presented that the threat of folivorous agents to eggplant cultivations may have been overrated and prospects for the eventual release of these oligophagous agents are discussed.