Effects of intercropping systems on community composition and diversity of predatory arthropods in vegetable fields

Field trials were carried out on Langqi Island, Fujian, PR China in 2004, to determine the effects of intercropping Chinese cabbage (Brassica chinensis) with green cabbage (Brassica oleracea), garlic (Allium sativum) and lettuce (Lactuca sativa), on community composition and diversity of predatory arthropods in vegetable fields. Two intercropping plots were designed and used in this study. In plot 1, two ridges of Chinese cabbage were intercropped with one ridge of garlic (CG1), lettuce (CL1) or green cabbage (CB1). In plot 2, the Chinese cabbage was planted in the center (100 cm wide) of the ridge, and under-sown with garlic (CG2), lettuce (CL2) or green cabbage (CB2) on both edges (25 cm wide) of the same ridge. A monoculture plot of the Chinese cabbage (CK) was arranged for comparison with plots 1 and 2. The highest species richness was found in CG1, and the lowest in CK. The highest abundance was found in CL1 (141.67 predators/plot), whereas the lowest was in CB1 (97.67 predators/plot). With the exception of CL1, significantly higher diversity indices were found in intercropping treatments than in CK. The majority of spiders sampled from fields were from families Theridiidae (34.04%) and Lycosidae (30.57%). These findings suggest that Chinese cabbage intercropped with non-cruciferous crops might increase species richness, abundance and diversity of the arthropod community in general and predators in particular.