Assessing the risks of releasing a sap-sucking lace bug, <Emphasis Type="Italic">Gargaphia decoris</Emphasis>, against the invasive tree <Emphasis Type="Italic">Solanum mauritianum</Emphasis> in New Zealand

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. Handling editor: John Scott.     

Assessing the risks associated with the release of a flowerbud weevil, Anthonomus santacruzi, against the invasive tree Solanum mauritianum in South Africa

Biological control of Solanum mauritianum Scopoli, a major environmental weed in the high-rainfall regions of South Africa, is dependent on the establishment of agents that can reduce fruiting and limit seed dispersal. The flowerbud weevil, Anthonomus santacruzi Hustache, is a promising fruit-reducing agent, despite ambiguous results obtained during host-specificity evaluations in quarantine. Adult no-choice tests showed that although feeding is confined to Solanum species, normal feeding and survival occurred on the foliage (devoid of floral material) of cultivated eggplant (aubergine), potato, and several native South African Solanum species. During paired-choice tests, involving floral bouquets in 10-liter containers, A. santacruzi oviposited in the flower buds of 12 of the 17 test species, including potato and eggplant, although significantly more larvae were recovered on S. mauritianum than on eight other species. Larvae survived to adults on all 12 species, with survival significantly lower on only four species than on S. mauritianum. However, during multi-choice tests, involving potted plants in a large walk-in cage, A. santacruzi consistently displayed significant feeding and oviposition preferences for S. mauritianum over all of the 14 Solanum species tested. Analyses of the risk of attack on nontarget Solanum plants suggested that, with the possible exception of two native species, none is likely to be extensively utilized as a host in the field. Also, host records and field surveys in South America have suggested that A. santacruzi has a very narrow host range and that the ambiguous laboratory results are further examples of artificially expanded host ranges. These and other considerations suggest that A. santacruzi should be considered for release against S. mauritianum in South Africa, and an application for permission to release the weevil was submitted in 2003.