Effects of planting pattern of collards on resistance to whiteflies (Homoptera : Aleyrodidae) and on parasitoid abundance

Fourteen collard entries, Brassica oleraceae L., Acephala group, were evalu ated for resistance to natural populations of Bemisia argentifolii Bellows & Perring in replicated field plots in Charleston, SC. Glossy-leaf phenotyp es ('SC Glaze', 'SC Landrace', 'Green Glaze') were the most resistant colla rd entries and had fewer whiteflies than the nonglossy, open-pollinated cul tivars. Also, two F-1 hybrid cultivars with normal, nonglossy leaves ('Blue Max' and 'Top Bunch') were resistant. In laboratory experiments, there wer e no differences in the intrinsic rate of growth (r(s)) of B argentifolii p opulations on either glossy or nonglossy collard phenotypes. Over a 2-yr pe riod, there were no differences in the abundance of whiteflies on the gloss y phenotype of Green Glaze when it was planted in solid 20-plant plots or w hen it was alternated (every other plant) with the nonglossy phenotype of G reen Glaze, In a similarly designed experiment, there was no difference in the resistance of Blue Max in either solid or mir;ed planting scheme compar ed with the susceptible 'Morris Heading'. Higher numbers of whiteflies and parasitoids (primarily Eretmocerus spp.) were collected on yellow sticky ca rds in the solid plantings of the nonglossy phenotype of Green Glaze than w ere collected in the solid plantings of the glossy Green Glaze phenotype. C ounts on sticky cards in the mixed plots were intermediate. These data show that planting pattern of collard entries is relatively unimportant in the deployment of these sources of host plant resistance. The data also suggest that nonpreference is the primary mode of resistance to whiteflies for cer tain collard entries.