Plant Resistance to Insect Attack in Commercial Cabbage Varieties1

Abstract

Field studies on the relative resistance of various commercial cabbage varieties to attack by the cabbage maggot, Hylemya brassicae (Bouché); the imported cabbageworm, Pieris rapae (L.); the cabbage looper, Trichoplusia ni (Hübner); and the cabbage aphid, Brevicoryne brassicae (L.), were conducted at Kenosha, Wisconsin, between 1958 and 1962. Significant differences were found in the relative resistance of the various cabbage varieties to all insect species studied. The most susceptible varieties were 2 to 10 times as severely infested as the most resistant varieties depending on the insect species and life stage considered. The factor or factors which determine host selection by the various insect species apparently operated independently since a cabbage variety relatively resistant to one insect species might be quite susceptible to another. Nonpreference was the primary mechanism of resistance to both the imported cabbageworm and the cabbage looper. Larval populations of both species closely reflected the ovipositional preferences of the adult. Varietal differences in host suitability were of greater significance than host selection in determining the relative resistance to both the cabbage maggot and the cabbage aphid. The red cabbage varieties proved decidedly less susceptible to imported cabbageworm oviposition than the green varieties. Color or a color-related factor appeared to be of primary significance in determining host preferences for this species. Seasonal shifts in the relative susceptibility of the various varieties were observed for the imported cabbageworm and the cabbage aphid. The data suggests that the red varieties favor establishment and survival of the impoted cabbageworm and increase of the cabbage aphid.