Abstract
In Hokkaido, petioles of Japanese butterbur, Petasites japonicus, are heavily injured by some syrphid larvae, whose specific names are unclear. In this study, I clarified the biology of two species of Cheilosia in butterbur in Hokkaido. Young larvae of both species attack the inner side of petiole from May to July, and then mature larvae bore downward to the subterranean stalk. C. yesonica was dominant in the edibie petiole and was likely to be univoltine, whereas C. fluvipes was bivoltine. Both species overwintered in the pupal stage in the shallow soil near injured butterburs, and emerged in spring. They could be distinguished by the shape and the number of spiracular openings of the posterior respiratory process in mature larvae or pupae.
