Selection of biological control agents for bridal creeper: a retrospective review

Abstract  We reviewed in retrospect the selection process of agents for the biological control of bridal creeper ( Asparagus asparagoides ) in Australia. Selection of agents was facilitated by first investing resources, mostly in South Africa, to clarify identification of the target weed, locate most suitable areas to search for natural enemies, make preliminary observations on phenology, host range and impact of natural enemies and experimentally demonstrate indirect impact of a foliage feeder on below-ground biomass of bridal creeper. Although only limited climate modelling was performed to predict abundance of prioritised agents in Australia, their widespread distribution in South Africa was a good indication that they were likely to establish. No attempts were made to predict possible levels of parasitism that could be encountered in Australia and no formal assessment was undertaken to decide in what order prioritised agents should be released. Three of the four agents prioritised have now been released in Australia. The rust fungus Puccinia myrsiphylli (Thüm.) G. Winter and leafhopper Zygina sp. have widely established and have already demonstrated their capacity to reduce significantly density of bridal creeper populations. It is still too early to determine the contribution that the third agent released, the Crioceris sp. leaf beetle, will make to the program.