Varietal Resistance to Insect Attack in Various Cruciferous Crops1

Abstract

The relative resistance to insect attack of 43 varieties of Cruciferae representing 11 different Brassica crops, including 16 green and 5 red varieties of cabbage, were studied in field experiments conducted at Kenosha, Wisconsin, in 1960. Evaluations were made of the relative insect resistance of the various varieties to the cabbage maggot, Hylemya brassicae (Bouche); the imported cabbageworm, Pieris rapae (L.); the diamondback moth, Plutella maculipennis (Curtis); and the cabbage looper, Trichoplusia ni (Hubner). In the varieties screened, a considerable range of relative resistance was observed for each of the insect species studied. With few exceptions the relative level of resistance was found to be primarily a characteristic of the crop species and secondarily one of variety. The relative resistance of the different varieties to each of the insects was independent of the level of resitance to any other species; the mechanisms of resistance being different for each insect considered. Host selection could not be correlated with plant size for any of the insect pecies studies. In the cabbage varieties host selection by the imported cabbageworm was found to be related to foliage color; the red cabbage varieties being less susceptible to oviposition than any of the green varieties. Larval survival of this species was, however, favored on the red cabbage varieties, the larva/egg ratios being higher on these varieties than on the green cabbages.