Cold hardiness and overwintering survival of the cabbage seedpod weevil, Ceutorhynchus obstrictus

The cabbage seedpod weevil, Ceutorhynchus obstrictus (Marsham) (Coleoptera: Curculionidae), is a serious pest of brassicaceous crops in temperate regions and a chronic member of the pest complex that attacks canola in Canada. We conducted several laboratory and field experiments to quantify winter survival and its role in the population dynamics of this insect. We estimated the supercooling point of the weevil at -7 [degree]C and its survival over 8 weeks decreased significantly at -5 [degree]C relative to 5 [degree]C, but extending the overwintering period at 5 [degree]C to 18.5 weeks had no effect on mortality. Cumulative sub-freezing degrees estimated from air temperature, and especially from soil temperature, were highly correlated with weevil survival. Our linear regression model predicted poor survival of the weevils in typical winters in northern Alberta. Our results indicate that if milder winters prevail, as predicted by global warming, there is potential for the weevils to establish and become a serious pest in northern canola-growing regions of Canada.