Nutritional Effects on the Appearance of Canola and its Attractiveness to the Cabbage Seedpod Weevil

To investigate visual cues as a mechanism to explain phytophagous insect intraspecific host selection and to explain the effects of plant nutrition on visual cues associated with host selection we assessed the response of the cabbage seedpod weevil, Ceutorhynchus obstrictus, to plants of canola (oilseed rape), Brassica napus supplied with varied nitrogen (N) rates and sulfur to nitrogen (S:N) ratios. We assessed the effects of these treatments on B. napus appearance using photography and spectrophotometry. Plant nutrition had a significant effect on C. obstrictus; host plant attractiveness declined with increasing S:N ratios. We found strong evidence that attractiveness of host plants to C. obstrictus was mediated by several components of B. napus appearance supporting the role of visual cues in intraspecific host selection.