Cabbage Leaf Epicuticular Wax Deters Female Oviposition and Larval Feeding of Pieris rapae

The small white butterfly Pieris rapae is a major pest of brassicaceous crops, causing extensive damage to cabbage Brassica oleraceae var. capitata. Pieris rapae utilizes glucosinolates, which are characteristic of brassicaceous plants, for host selection. However, the effect of epicuticular wax of cabbage leaves on host selection by P. rapae remains unclear. This study was aimed to determine the effects of leaf epicuticular wax on female oviposition and larval feeding of P. rapae. We used a common cabbage variety 'Kinkei 201' containing n-nonacosane as the predominant leaf wax component. Wax removal treatments, in which the leaf surface was rubbed with cotton balls, significantly increased female oviposition and mid-stage (2nd-4th instars) larval feeding compared with untreated (intact) leaves. Spraying treatments with n-nonacosane standard on wax-removed leaves significantly suppressed female oviposition and mid-stage larval feeding. Thus, n-nonacosane in cabbage leaf epicuticular wax potentially affects host selection and preference by P. rapae. In contrast, final-stage (5th instar) larvae significantly preferred intact leaves to wax-removed leaves, and spraying treatments with n-nonacosane did not significantly change their feeding on wax-removed leaves. This suggests that young larvae are more susceptible to wax feeding inhibition than older larvae and that increasing leaf wax content enhances the resistance of cabbage against P. rapae. Acquiring these traits in cabbage leaves through improved breeding and cultivation methods may reduce and control the oviposition and feeding damage by P. rapae.