The insect fauna of Canada thistle, Cirsium arvense (L.) Scop. in southern Montana

Insects associated with Cirsium arvense (I.) Scop, in southern Montana are reported.Fifty-six phytophagous species, and 47.visiting insects were collected, identified and tabulated.Four insect species, Corythucha d istincta Osborn and Drake (Hemiptera: Tingidae), Bans sp., poss.c irs ii Gilbert (Coleoptera: Curculionidae), Vanessa^cardui L. (Lepidoptera: Nyrnphalidae),.and Orellia ruficauda (Fabricius)(Diptera: Tephritid a e ), were considered, conspicuous, because of th e ir damage inflicted to the th is tle plant.More insects were found associated with the-developing seed heads than with foliage, stems or roots.The information gathered oh.this local survey can be valuable for future introductions of insect, biological control agents.It forms the foundation for follow-up studies with indigenous insect species.Augmentation and redistribution of established monophagous insects such as Ceuthorynchus litura and Baris sp.should, be considered.Trans mission experiments are necessary to evaluate the potential of these' monophagous insects, as th is tle pathogen vectors.The combination of .two stress-factors will increase the impact on the th is tle plant in .the fie ld .-