Reproductive Biology of Ceutorhynchus obstrictus (Coleoptera: Curculionidae) on Wild and Cultivated Brassicaceae in Southern Alberta

Abstract

Mated and gravid status were assessed for early-season populations of Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae) on wild and cultivated Brassicaceae in southern Alberta, Canada. Mated female C. obstrictus were found in the first samples examined (22 May 2001). At least 84% of C. obstrictus dispersing to wild host sites up to 23 May 2001 (captured using yellow pan traps) were males. Females of C. obstrictus with at least one egg in the lateral oviducts were first encountered on 6, 8 and 18 June 2001 on Descurainia sophia (L.) Webb, Sinapis arvensis L., and Cardaria spp., (Brassicaceae), respectively. Females on S. arvensis, a true host with pods that can sustain larvae, had more robust ovary development than females on Cardaria spp. and D. sophia, food hosts with pods that cannot sustain larvae. The most fecund sample (n = 30) from S. arvensis was collected on 24 June 2001 when 80% of females had a mean of 7.2 ± 2.7 (±SD) eggs in the lateral oviducts. The most fecund full samples (n = 30) from Cardaria spp. and D. sophia had 6.7% and 40.0%, respectively, of females with at least one egg in the lateral oviducts, and an overall maximum of four eggs in the lateral oviducts per female. There is no apparent reproductive advantage to C. obstrictus in developing eggs on early-season food hosts, although food hosts likely play an important role in sustaining C. obstrictus until true hosts are encountered. Although gravid status was high in females on S. arvensis, this host supported relatively few larvae. The highest infestation level of C. obstrictus per sample of S. arvensis pods in 2001 was 13.5% (n = 891 pods) based on the presence of eggs, larvae, and exit holes. A sample of volunteer Brassica napus L. (Brassicaceae) pods (n = 100) had a 77% infestation level. The apparent discrepancy between the relatively robust gravid status of C. obstrictus on S. arvensis, and low pod infestation, was explained as a combination of factors that likely include an inherent unsuitability of wild S. arvensis pods for C. obstrictus. However, given the wide distribution of S. arvensis in southern Alberta, this wild true host would likely maintain low populations of C. obstrictus in the absence of volunteer and spring-seeded cultivated hosts.