Biological control of Canada thistle (Cirsium arvense) revisited: host range of Hadroplontus litura on Cirsium species native to the Upper Midwest, USA

In 1998, Hadroplontus (formerly Ceutorhynchus) litura, a stem-mining weevil, was introduced into a limited area in Minnesota for the biological control of Canada thistle, Cirsium arvense. Although showing a preference for C. arvense, initial host range testing in the 1960s indicated H. litura attacked other native Cirsium species. Before promoting or augmenting biocontrol with H. litura in Minnesota, we wanted to further define the host range of H. litura on native Cirsium species. Our objective was to determine whether H. litura could feed, oviposit and complete development on Cirsium spp. native to the Upper Midwest of the USA. In no-choice tests, female H. litura accepted all native Cirsium species for oviposition. In addition, H. litura was able to complete development to the adult stage on swamp thistle, Cirsium muticum, field thistle, Cirsium discolour, and tall thistle, Cirsium altissimum, and we confirmed the published host range test results of completed development on Flodman’s thistle, Cirsium flodmanii. These Cirsium species are within the fundamental host range of H. litura. No adults were found in development tests with Hill’s thistle, Cirsium pumilum var. hillii, a threatened or species of concern in the Upper Midwest, or Pitcher’s thistle, Cirsium pitcheri, a federally listed threatened species. Larval tunnelling was documented in C. pitcheri. We recommend that field tests be conducted, where search and host acceptance behaviour can occur under field conditions to further define the ecological host range of H. litura.