IMPORTANCE OF PREINTRODUCTION SURVEYS IN THE BIOLOGICAL-CONTROL OF SOLANUM WEEDS IN SOUTH-AFRICA

Three exotic Solanum weeds, Solanum elaeagnifolium Cav., Solanum mauri tianum Scop. and Solanum sisymbriifolium Lam. (Solanaceae), are target s for biological control in South Africa, Preintroduction surveys of t he insect herbivores attacking these, as well as native and cultivated species of Solanum, have proved useful in several ways. Although ther e is a diverse, mainly oligophagous, herbivore fauna on native Solanum spp., that of the exotic weeds is mainly polyphagous and low in diver sity and numbers. Feeding niches on introduced weeds are either vacant or underutilized, ensuring a wide scope for the selection of exotic b iocontrol agents. Similarities between potential agents and native Sol anum herbivores suggest that the former may recruit native parasitoids , a fact that has to be considered in the selection process. The surve ys also helped to resolve a conflict of interest, caused by most candi date agents accepting the introduced crop plant Solanum melongena L. ( eggplant) in specificity tests. Although a number of native Solanum ol igophages attacked neglected eggplant fields, damage to crops is precl uded by the pesticide regimes aimed at several generalist pests. Impor ted agents are no more a risk than native Solanum feeders, which are n ot regarded as pests. The surveys support the view that exotic agents should be introduced to control Solanum weeds.