Phenologies of Canada thistle (<i>Cirsium arvense</i>) and <i>Cirsium</i> species native to the upper Midwest: implications for the ecological host range of the biocontrol agent <i>Hadroplontus litura</i>

Abstract Native Cirsium species play an important role in landscapes across North America. Hadroplontus litura (F.) (formerly Ceutorhynchus ), the stem-mining weevil and biological control agent of Canada thistle [ arvense (L.) Scop.] can complete its life cycle on five native to upper Midwest. Although these are within fundamental host range H. , as determined by host-range tests, we wanted explore whether phenological differences among help define field ecological . The objective this study was determine phenology Midwest relation C. litura. Our goal shoots could escape shoot oviposition spring due delayed emergence relative Soil cumulative growing degree days (GDD) were a superior predictor for perennial or initiation leaves biennial species, with 2.4 times larger effect time air GDD. All initiated new before emergence, even when growth spring. In turn, emerged approximately 1 3 wk female began lay eggs. As such, all plants had available oviposition. There no separation between that would render safe from attack. Based spring, tested be