Making host specificity testing more efficient: Exploring the use of abridged test plant lists

Testing the specificity of candidate agents is a key component of risk analysis in weed biological control. This step is often time-consuming due to the numerous plant species that need to be tested under quarantine conditions in the invaded country of the weed species. Here, we examined whether an abridged phylogenetically based test list could be used in the weed's native range to quickly screen the host specificity of candidate agents. Ten plant species were used to test the host specificity of a promising candidate for the biological control of Sonchus oleraceus in Australia, the gall midge, Cystiphora sonchi. No-choice and choice tests were carried out in the native Mediterranean range of the midge. The results showed the midge has potential to threaten native Australian species, as those species showed high infestation levels in no-choice tests and produced significantly higher numbers of galls in choice tests. As a result of this approach, C. sonchi was rapidly discarded from the list of agents to be imported into Australian quarantines for further tests. This study demonstrates that testing a few key phylogenetically related species in the native range may save cost and effort in a weed biological control programme.