Host specificity and impacts of Platyptilia isodactyla (Lepidoptera: Pterophoridae) a biological control agent for Jacobaea vulgaris (Asteraceae) in Australia and New Zealand

<i>Jacobaea vulgaris</i> Gaert. (ragwort) is a serious noxious weed of high fertility pastures in high rainfall regions of southern Victoria and Tasmania in Australia. Biological control of <i>J. vulgaris</i> in Australia has been underway since the 1930s. Overseas explorations in Europe identified the ragwort plume moth, <i>Platyptilia isodactyla</i> Zeller as a potential biological agent. The host specificity of <i>P. isodactyla</i> was tested to determine its safety. Seventy-three plant taxa were screened for <i>P. isodactyla</i> phytophagy and survival. <i>P. isodactyla</i> development and survival was restricted to a few taxa in the tribes Senecioneae and Asterae, but was negligible on species other than <i>J. vulgaris</i>. <i>P. isodactyla</i> showed only weak oviposition preference for <i>J. vulgaris</i> but this behavior may have been affected by confined test conditions. Only <i>J. vulgaris</i> was able to support continued <i>P. isodactyla</i> population growth. <i>P. isodactyla</i> was released for biological control of <i>J. vulgaris</i> in Australia during 1999 and in New Zealand during 2005. Field site damage assessments have shown that <i>P. isodactyla</i> can have substantial impact on <i>J. vulgaris</i> flowering and survival. A survey of Senecio species in close proximity with <i>J. vulgaris</i> attacked by <i>P. isodactyla</i> during 2004 showed no off-target impacts. <i>P. isodactyla</i> is well established in both Australia and New Zealand. Its ability to survive on <i>J. vulgaris</i> in wetter habitats is expected to complement other biological control agents enabling it to make a significant contribution to <i>J. vulgaris</i> suppression in Australia and New Zealand.