Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2006
Publication Date: 4/1/2007
Citation: Balciunas, J.K. 2007. Lixus Cardui, a Biological Control Agent for Scotch Thistle (Onopordum acanthium): Safe for Australia but not USA?. Biological Control. 4(11):134-141. Interpretive Summary: Weeds cause large environmental and economic losses in the USA. Scotch thistle (Onopordum acanthium) is a widespread weed that is especially damaging in the arid portions of the Northwest, California and Nevada. This tall thistle can reach 12 feet in height, and dense stands prevent passage of cattle, wildlife, and humans. This article reports on research to determine if a weevil from Europe that severely damages Scotch thistle is safe enough to release in the USA as a biological control agent for this weed.
Technical Abstract: 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 Lixus 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 Lixus 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 Lixus cardui were terminated, and I will not seek its release in the United States. Even though, Lixus 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.