Lixus cardui, a biological control agent for scotch thistle (Onopordum acanthium): Safe for Australia, but not the USA?

Invasive exotic plants are often weeds in more than one country. After a biological control agent for a weed has been developed for use in one country, it is reasonable to consider using the same agent against the same weed in another country. ‘Transfer Projects’ can save considerable time and money, and they have been popular around the world. Lixus cardui Olivier (Coleoptera: Curculionidae), a weevil from Europe, was first used by Australian researchers to control Scotch thistle, Onopordum acanthium L. (Asteraceae). There are few close relatives of Scotch thistle in Australia, but that is not the case in North America, where scotch thistle is also an important weed. I initiated a project to test some of the agents released in Australia to see if they would be appropriate for release in the United States. Test plants, primarily Cirsium spp. thistles native to California, were exposed under both choice and no-choice conditions to two populations of L. cardui, one from Greece, the other from France. The latter may represent an undescribed species, and its test results are reported separately. Both strains of L. cardui weevils fed heavily and developed on some native North American thistles, at a level comparable to the target weed, Scotch thistle. Consequently, our laboratory colonies of L. cardui were terminated, and I will not seek its release in the United States. Even though, L. cardui has established well in Australia since its release in 1993, and dispersed widely there without causing problems, it is inappropriate to release it in the United States. Published by Elsevier Inc.