Biology, host specificity and risk assessment of Gargaphia decoris, the first agent to be released in South Africa for the biological control of the invasive tree Solanum mauritianum

The South American tree Solanum mauritianum is a major environmental weed in the high-rainfall regions of South Africa and has been targeted for biological control since 1984. Although host ranges of imported agents determined during quarantine tests have resulted in the rejection of eight of the 11 candidate agents tested so far, the leaf-sucking lace bug Gargaphia decoris, imported from Argentina in 1995, displayed an acceptably narrow host range in captivity. No-choice tests showed that G. decoris is confined to Solanum species and cannot survive on solanaceous crops outside that genus. Although these tests also indicated that G. decoris colonies could survive and reproduce on cultivated eggplant (aubergine) and at least five native South African Solanum species, all but one native species proved to be inferior hosts in terms of adult survival and oviposition potential. During paired choice and multichoice tests in small and larger cages respectively, G. decoris displayed very strong feeding and oviposition preferences for S. mauritianum. Analyses of the risk of attack on non-target Solanum plants revealed that, with one possible exception, none were likely to suffer more than incidental damage in the field. Host records from South America have also indicated that G. decoris has not been recorded on any Solanum species other than S. mauritianum, providing further evidence of its host specificity. The results of this study were accepted by the regulatory authorities and in February 1999, G. decoris became the first agent to be released in South Africa for the biological control of S. mauritianum.