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.

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In South Africa, the leaf-feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chyrsomelidae), was released in 2013 against the invasive annual herb Parthenium hysterophorus L. (Asteraceae: Heliantheae). Poor field establishment and variable incidence of the beetle, during the first few years after release, have led to concerns surrounding potential constraints, including host plant quality. This study assessed the influence of high, medium and low host plant quality, as influenced by fertiliser application, on the survival, development and fecundity of Z. bicolorata. Although egg to adult survival was high (∼80%) and did not differ between plant quality treatments, larvae developed fastest on plants of high and medium quality. Larval feeding was highly damaging, reducing the growth, reproduction and biomass of P. hysterophorus in all three plant quality treatments. Fecundity was associated with plant quality, with larger, more fecund females developing on higher quality plants. Overall, this research may aid current mass-rearing efforts, further field research to verify these findings and direct the selection of more suitable release sites for Z. bicolorata in South Africa.

h i g h l i g h t sGargaphia decoris herbivory reduced photosynthesis of Solanum mauritianum in both shaded and fullsun conditions. Photosynthesis declined due to chlorophyll removal and, indirectly, through physiological impairment. Herbivory rates were greater in the shade but feeding was more damaging in sun plants. Given the agent's potential effectiveness for biological control, factors constraining its performance need to be addressed.

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