Classical biological control of Californian thistle: the New Zealand story

摘要

Californian thistle (Cirsium arvense (L.) Scop.) is ranked as one of the world's 80 worst weeds and costs the Southland region of the South Island, New Zealand, NZ 27 million dollar annually. A group of farmers and farming-associated organisations inOtago and Southland formed a trust called the Californian Thistle Action Group (CalTAG) and applied for community funds to 'improve the control of Californian thistle using natural enemies'. This group funded CABI Bioscience in Europe to survey for potential new biocontrol agents. Its aims also included assessing the current status of biocontrol agents in New Zealand, and evaluating the effectiveness of current control methods (mowing, spraying and grazing). Three agents (Altica carduorum Guerin-Meneville 1858, Lema cyanella Linnaeus 1758, and Urophora cardui Linnaeus 1758) have been released into New Zealand for the biological control of Californian thistle but they either failed to establish or had little impact on populations of this thistle. For example, after four years of caged rearing and farmer involvement from the Otago and Southland regions, the gall-forming fly U. cardui has failed to establish in large numbers. Through additional community funding a new agent (Apion onopordi Kirby 1808) was imported and tested for host specificity in 2002/03. This root- and stem-feeding weevil is a vector for the C. arvense rust, Puccinia punctiformis (Str.) Rohl. Host testing has shown that the weevil can attack plant species within the tribe Cardueae, potentially including the minor crop species safflower (Carthamus tinctorius L.) and globe artichoke (Cynara scolymus L.). This paper outlines the process of forming and funding a community group project in New Zealand, and the ups and downs of the biological control of this major pasture weed.