A review of Solanum mauritianum biocontrol: prospects, promise and problems: a way forward for South Africa and globally

Abstract

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.

Ecological niche modelling of Gargaphia decoris (Heteroptera), a biological control agent of the invasive tree Solanum mauritianum (Solanales: Solanaceae)

“…This should be taken into account when interpreting the ENM trained with the native records. Most of the release sites with unconfirmed establishment fell within areas predicted to have suitable conditions, and those outside this range were quite close (the farthest is 22 km away), so considering that the model might be somewhat overfitted, the possibilities of successful establishment should not be discarded …”

“…To date, cold winter temperatures were believed to be one of the reasons for the low population densities in South Africa, as low temperatures reduce the quality of S. mauritianum foliage . All the previous evidence suggests that this is not so.…”

“…Solanum mauritianum has become naturalized in Africa, Australasia, India and islands in the Atlantic, Indian and Pacific oceans, presumably via the Portuguese trade routes in the early 16th century . The tree has reached invasive status in several countries . Within these invaded countries, S. mauritianum is particularly problematic in conservation areas, agricultural lands, forestry plantations and riverine habitats .…”

“…Conventional control approaches such as chemical or mechanical methods are not cost‐effective on a large scale. Thus, biological control is considered one of the few sustainable options to effectively control invasion by this plant over time and space …”

“…However, this was dismissed following thermal assessments by Barker and Byrne who found that the insect was not directly affected by the cold temperatures . Currently, predation is considered to be a major factor constraining G. decoris populations …”