Effects of Iberis umbellata (Brassicaceae) on Insect Pests of Cabbage and on Potential Biological Control Agents

Abstract

Noncrop borders surrounding field crops may enhance biological control of insect pests by drawing pests away from the crop and by providing a suitable habitat for natural enemies. We quantified the effects of borders of flowering Iberis umbellata L. (candytuft) on cabbage pest and predator abundance by repeatedly sampling arthropod abundance in plots of Brassica oleracea L. I. umbellata provides potential food for crucifer herbivores as well as nectar and pollen resources for predators. Although I. umbellata harbored large populations of hemipteran predators, few of these predators were found on the adjacent crop plants. Iberis borders did not change the abundance of crop pests within the crop but had mixed effects on natural enemies. Interestingly, the spatial distribution of Pieris rapae L. and Trichoplusia ni (Hübner) eggs on B. oleracea differed significantly between treatments, indicating that the presence of flowering I. umbellata may have altered the movement and oviposition behavior of these lepidopteran pests. Our results point to the importance of considering predator and pest movement when investigating how alternative habitats, such as flowering borders, affect arthropod population dynamics.