Biology, host specificity and risk assessment of the leaf-mining flea beetle, Acallepitrix sp nov., a candidate agent for the biological control of the invasive tree Solanum mauritianum in South Africa

摘要

The South American tree Solanum mauritianum, a major environmental weed in the high-rainfall regions of South Africa, has proved to be a difficult target for biological control. Artificially expanded host ranges of candidate agents during quarantine host-specificity tests, have resulted in the release of only one agent species which has so far had a negligible impact on the weed. The necessity for additional agents resulted in the importation of a leaf-mining flea beetle, an unidentified species of Acallepitrix, from Brazil in 1997. No-choice tests in quarantine showed that potential host plants are confined to the genus Solanum. Although several non-target plants, including cultivated eggplant ( aubergine) and some native South African Solanum species, sustained feeding, oviposition and the development of larval leaf mines, most of these were inferior hosts. These results were confirmed by paired choice tests, where Acallepitrix sp. nov. displayed significant feeding and oviposition preferences for S. mauritianum and where, with few exceptions, more larval leaf mines were initiated on S. mauritianum. Interpretation of the host-specificity tests was facilitated by a risk assessment matrix which suggested that the risk of feeding and oviposition on non-target Solanum plants, including eggplant cultivations, was relatively low. These and other considerations, such as the lack of evidence of damage inflicted on cultivated Solanaceae in South America, suggest that Acallepitrix sp. nov. could be considered for release against S. mauritianum in South Africa. However, the results of the host-specificity tests remain ambiguous and until more compelling evidence is obtained from field surveys and open-field trials in Brazil, an application for permission to release the flea beetle in South Africa will not be considered.