Gratiana lutescens (Boheman) (Coleoptera: Chrysomelidae: Cassidinae) reconsidered as a natural enemy of satansbos, Solanum elaeagnifolium Cavanilles (Solanaceae), in South Africa

Solanum elaeagnifolium Cavanilles is a weed in low-rainfall agricultural areas of South Africa and is a target for biological control. The leaf-feeding tortoise beetle, Gratiana lutescens (Boheman), was first considered as a biological control agent for S. elaeagnifolium in the early 1970s, but was rejected because it developed on eggplant and an indigenous Solanum species during larval no-choice tests on cut leaves. This insect was re-imported in the late 1980s and larval no-choice tests were carried out on potted plants. The results were compared to those of cut leaves and indicated that the insect could be reconsidered for introduction. Gratiana lutescens was re-imported from Argentina in 1995 for the present study and host specificity was determined using larval no-choice tests on whole plants, and less conservative paired- and multi-choice tests using adults. Gratiana lutescens was able to develop on a wide range of Solanum species. Although adult choice tests indicated a narrower and possibly more realistic host range, the potential of this insect to oviposit and develop on indigenous Solanum species and eggplant indicates that it is not suitable for release as a natural enemy for S. elaeagnifolium in South Africa.