Rhinocyllus conicus: Initial evaluation and subsequent ecological impacts in North America

Renewed debate over the risk of non-target effects in biological control re flects, in part, the recent quantification of direct and indirect ecologica l effects of the flowerhead weevil, Rhinocyllus conicus Frol., in North Ame rica. To help resolve the issue, we review the published data for R. conicu s from both Europe and North America: pre-release (1961-1968), post-release (1969-1985) and more recent (1986-1999). Our aim was to determine the exte nt to which host range expansion on to native North American species, and t he associated ecological effects, were predicted or predictable. Our overal l conclusion is that more was known than is generally realized, Yet more in formation would have been required to complete the initial assessment of ec ological consequences. Three important points emerge. First, the potential effect of R. conicus on native North American species was not a major eleme nt of the testing programme. Second, the host range expansion observed is c onsistent with the pre-release and early post-release data, and so was pred ictable, if not predicted. The pre- and early post-release data showed that R. conicus could feed and develop on multiple Cirsium species, including t wo North American species. Third, we found that tile studies needed to quan tify the likely magnitude of feeding by R. conicus on North American Cirsiu m species, and thus the ecological consequences of that feeding, were not d one. Instead, inferential arguments were used to suggest that any feeding b y R. conicus on North American species would not be substantial. We conclud e that there were sufficient data, which suggested that North American Cirs ium species would be acceptable host species, to have warranted further tes ting to define and quantify the potential ecological side-effects of introd ucing P, conicus to North America. Contemporary concerns should now mandate such tests.