Application for release of R. conicus was submitted to a
Federal-State review committee in 1967. It was clearly
stated that both native and introduced Cirsium spp. were
likely to support development of R. conicus (Schroeder,
1980; Zwölfer, 1967; Zwölfer and Harris, 1984). The release
Following release, R. conicus established readily, spread
by itself, and was also redistributed widely by cooperators .
R. conicus severely impacted Carduus thistles and contributes
signiWcantly to their management. Impact on native
Cirsium spp. has been detected (Louda et al., 1997), as was