The invasive tree Solanum mauritianum Scopoli remains one of the world's most widespread environmental weeds. Despite biocontrol providing one of the few viable long-term solutions to tackling S. mauritianum invasions globally, only South Africa and, more recently, New Zealand, have programmes in place. Ongoing biocontrol efforts against S. mauritianum are reviewed here with particular reference to South Africa. The South African programme has suffered a troubled history, with considerable research efforts culminating in the eventual release and establishment of only two insect agents, Gargaphia decoris Drake and Anthonomus santacruzi Hustache. The difficulties experienced have hindered research into new agents, causing apprehension in using biocontrol internationally. However, recent studies have demonstrated that biocontrol may be deserving of renewed investment, particularly within an integrated management context. In this review, we advocate for the revival of the S. mauritianum biocontrol programme in South Africa, and discuss possible avenues for future research internationally.
The South American tree Solanum mauritianum Scopoli (Solanaceae), a major environmental weed in South Africa and New Zealand, has been targeted for biological control, with releases of agents restricted to South Africa. The leaf-sucking lace bug, Gargaphia decoris Drake (Tingidae), so far the only agent released, has become established in South Africa with recent reports of severe damage at a few field sites. To evaluate the insect's suitability for release in New Zealand, host-specificity testing was carried out in South Africa in laboratory and open-field trials, with selected cultivated and native species of Solanum from New Zealand. No-choice tests confirmed the results of earlier trials that none of the three native New Zealand Solanum species are acceptable as hosts. Although the cultivated Solanum muricatum Aiton and S. quitoense Lam. also proved unacceptable as hosts, some cultivars of S. melongena L. (eggplant) supported feeding, development and oviposition in the no-choice tests. Although eggplant was routinely accepted under laboratory no-choice conditions in this and previous studies, observations in the native and introduced range of G. decoris, open-field trials and risk assessment based on multiple measures of insect performance indicate that the insect has a host range restricted to S. mauritianum. These results strongly support the proposed release of G. decoris in New Zealand because risks to non-target native and cultivated Solanum species appear to be negligible. An application for permission to release G. decoris in New Zealand will be submitted to the regulatory authority.
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