No-choice risk assessment of Gratiana boliviana, a potential biological control agent of Solanum viarum in Australia

Abstract

ABSTRACT Tropical soda apple (Solanum viarum), first detected in Australia in 2010, is a weed of agricultural significance as it reduces cattle stocking rates and limits stock movement. Gratiana boliviana (Coleoptera: Chrysomelidae) is an approved biological control agent for S. viarum in the United States of America (USA). Although the host specificity of G. boliviana has been extensively tested in the USA, additional no-choice tests were conducted to determine if the beetle is sufficiently host specific for release in Australia. The host test list included Solanum species native to Australia, as well as agriculturally important species that had been tested previously. Both adult and larval no-choice tests indicate that G. boliviana does not perform equally well across the target weed S. viarum and the other plant species included in the tests. Oviposition was observed on only two plant species besides the target weed, with significantly more eggs laid on S. viarum (19.5 ± 0.4 eggs/plant), followed by S. brownii (2 ± 0.4 eggs/plant) and S. melongena (1.8 ± 1.5 eggs/plant). Ninety per cent of eggs laid on S. viarum developed to adults, whereas only one egg laid on S. melongena completed development. Larval no-choice feeding assessments indicate that larval survival and development is highest on S. viarum (80%) followed by S. brownii (30%) and S. melongena (20%) and to a much lesser extent on S. lithophilum (2.5%). Our results contribute to the evaluation of the risk of potential off-target effects by G. boliviana feeding and development on native Australian or agriculturally important Solanum species.