Floral characteristics affect susceptibility of hybrid tea roses, Rosa x hybrida, to Japanese beetles (Coleoptera: scarabaeidae)

Abstract

The Japanese beetle, Popillia japonica Newman, feeds on the flowers and foliage of roses, Rosa X hybrida. Beetles attracted to roses land almost exclusively on the flowers. This study evaluated characteristics of rose flowers including color, size, petal count and fragrance, as well as height of plants and blooms within plant as factors in attractiveness to Japanese beetles. Artificial flowers that had been painted to match the spectral reflectance of real blooms were attached to potted nonflowering rose plants in the field and the number of beetles that landed on each model was recorded. More beetles landed on the yellow- and white-colored flower models than on the five other bloom colors that were tested. Large (15 cm diameter) yellow flower models attracted more beetles than did smaller (8 cm diameter) yellow models. There was no difference in beetle response to yellow flower models of the same size that differed in bloom complexity (i.e., number of petals). Experiments in which blooming rose plants were elevated above controls, or in which flower models were placed at different heights within plant canopies, failed to support the hypothesis that height per se accounts for beetles' attraction to flowers over leaves. Attractiveness of selected rose cultivars that varied in fragrance and flower color also was evaluated in the field. Yellow-flowered cultivars were more susceptible than those with red flowers, regardless of fragrance intensity as rated by breeders. Growing cultivars of roses that have relatively dark and small-sized blooms may have some benefit in reducing Japanese beetles' attraction to roses.