Seasonal Incidence of the Cabbage Seedpod Weevil (Coleoptera: Curculionidae) on Rapeseed in West Tennessee

Abstract

Populations of the cabbage seedpod weevil, Ceutorhynchus assimilis (Paykull), were sampled in Fayette, Haywood, Henry, and Lake counties in seven and eight commercial rapeseed, Brassica napus spp. oleifera L., field sites in 1990 and 1991, respectively. The cabbage seedpod weevil was the most abundant (98.8%) of the eight curculionid species collected. Adult C. assimilis populations were monitored weekly from 7 April to 4 June 1990 and from 10 April to 4 June 1991. During early season, overwintering C. assimilis adult populations peaked on 27 April 1990 and 11 April 1991, respectively. Late in the season, adult C. assimilis (probable F1) populations peaked again on 4 June 1990 and 22 May 1991, respectively. Cabbage seedpod weevil populations were relatively low at sites in 1990; however, the total weevil population in Henry County was 79 times higher than that in Lake County in 1991. In the absence of commercial rapeseed fields, weevil densities in 1993 were 229 times greater on turnip, B. rapa L., in Henry County than in Lake County. A hypothesis for the higher weevil populations is that Henry County has more available alternate hosts and overwintering sites. Because rapeseed is new and C. assimilis is well adapted to this host, weevil infestations will likely increase and severely damage rapeseed stands as plantings increase in West Tennessee.