Banker plants promote functional biodiversity in cabbage

Abstract: Natural enemies of the cabbage whitefly Aleyrodes proletella do currently not regulate whitefly populations sufficiently. Biological control methods in field crops have often been neglected, although offering promising tools to increase the abundance and diversity of natural enemies. For instance, the release and promotion of natural enemies with banker plants is one way to increase functional biodiversity and biological control services in field crops. This field study investigated the following two banker plant systems against A. proletella: (1) the greenhouse whitefly Trialeurodes vaporariorum on pumpkin and (2) the honeysuckle whitefly A. lonicerae on European columbine. Both systems were inoculated with the parasitoid Encarsia tricolor. We evaluated the effect of the banker plant systems on A. proletella parasitism rates as well as the abundances of adult E. tricolor and predators on neighbouring Brussels sprouts plants. Both, average parasitism rates and adult E. tricolor increased by at least 50% by either banker plant systems. Furthermore, the abundance of hoverfly larvae was 63% higher in the treatment with pumpkin as banker plant compared to the control, whereas 11-12% fewer spiders were found in both treatments with banker plants. In conclusion, especially the banker plant system with T. vaporariorum and E. tricolor on pumpkin promoted functional biodiversity on cabbage plants and showed promising potential as banker plant system in cabbage crops.