EFFECTS OF IBERIS-UMBELLATA (BRASSICACEAE) ON INSECT PESTS OF CABBAGEAND ON POTENTIAL BIOLOGICAL-CONTROL AGENTS

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 b orders of flowering Iberis umbellata L. (candytuft) on cabbage pest an d predator abundance by repeatedly sampling arthropod abundance in plo ts of Brassica oleracea L. I. umbellata provides potential food for cr ucifer herbivores as well as nectar and pollen resources for predators . Although I. umbellata harbored large populations of hemipteran preda tors, few of these predators were found on the adjacent crop plants. I beris borders did not change the abundance of crop pests within the cr op but had mixed effects on natural enemies. Interestingly, the spatia l distribution of Pieris rapae L. and Trichoplusia ni (Hubner) eggs on B. oleracea differed significantly between treatments, indicating tha t the presence of flowering I. umbellata may have altered the movement and oviposition behavior of these lepidopteran pests. Our results poi nt to the importance of considering predator and pest movement when in vestigating how alternative habitats, such as flowering borders, affec t arthropod population dynamics.