Compost enhances parasitization of Brevicoryne brassicae (L.) by Diaeretiella rapae (M’Intosh) in broccoli under different levels of crop diversification and plant competition

Summary

The effects of intercropping via competition on crop biomass, pest [cabbage aphid Brevicoryne brassicae (L.)] abundance and natural enemy [the parasitoid Diaeretiella rapae (M’Intosh)] efficacy were studied in the Brassica oleracea L. var. italica system. From May to December 2004, insect populations and yield parameters were monitored in summer and fall in broccoli monoculture and polyculture systems with or without competition from Brassica spp. (mustard), or Fagopyrum esculentum Moench (buckwheat), and with addition of organic (compost) or synthetic fertilizer. Competition from buckwheat and mustard intercrops did not influence pest density on broccoli; rather, aphid pressure decreased and natural enemies of cabbage aphid were enhanced in intercropping treatments, but this varied with the intercropped plant and season (summer vs. fall). In compost-fertilized broccoli, increased seasonal parasitization rates of B. brassicae by D. rapae were observed along with the expected lower aphid pressure, when compared to synthetically-fertilized plants.