Life history, larval morphology, and nearctic distribution of Ceutorhynchus subpubescens (Coleoptera: Curculionidae)

Since the description of Ceutorhynchus subpubescens LeConte (Coleoptera: Curculionidae) >125 yr ago, very little information has been published on its biology, taxonomy, or distribution. We conducted studies in southern Alberta, Canada, to investigate aspects of its life history and host plant feeding preferences. Preimaginal life stages of C. subpubescens were described for the first time, and data were compiled on its North American distribution. Ceutorhynchus subpubescens was univoltine. Adults emerged from overwintering sites in shelterbelts in late April to early May, and first occurred on host plants in May. Eggs were laid into apical stem regions of flixweed, Descurainia sophia (L.) Webb (Brassicaceae), and hatched to larvae that mined the stems, feeding primarily on pith tissue. Three instars developed within D. sophia. When mature, the final instar bored an exit hole in the primary stem, just below the juncture of a lateral shoot. Developmental time from eggs to final instars required only 35- 45 d, an adaptation that accommodated the rapid development of D. sophia hosts. Setal numbers on the mouthparts and head capsule distinguished final instars of C. subpubescew from its sympatric congeners, Ceutorhynchus neglectus Blatchley and Ceutorhynchus obsttictus (Marsham). New distribution records for the species include Alberta, Arizona, Montana, Nebraska, New Mexico, Oregon, Saskatchewan, South Dakota, and Washington. C. subpubescew has adapted to exploit a resource-rich habitat, where larvae are free from interference from predators and parasitoids; however, its relatively rare occurrence in western North America is surprising given the abundance of its host plants.