Trap crop diversity enhances crop yield

Abstract

Diverse plantings provide many benefits for agroecosystem health. For example, ⿿trap crops⿿ that are highly attractive to pests can protect nearby, less attractive host plants. However, it is unclear whether increasing biodiversity of trap crops themselves might increase the effectiveness of this pest-management technique. We examined whether multi-species trap-crop plantings were more effective than any single species at protecting broccoli (Brassica oleracea var. italica) crops from the crucifer flea beetle, Phyllotreta cruciferae. Our trap crop plantings included between one and three plant species (Brassica juncea, Brassica napus, and/or Brassica rapa subsp. pekinensis), selected for their attractiveness to the beetles, while keeping total trap crop area constant. We found that only a diverse mix of all three trap-crops significantly improved yields of adjacent broccoli; indeed, the 3-species polyculture provided protection that exceeded that of a monoculture of the most effective single trap crop species. Furthermore, the protective effect of diverse trap crop plantings extended across the broccoli beds. Treating trap crops with an insecticide provided no further benefits for pest control or broccoli yields. Despite clear benefits of trap-crop diversity on yields, the number of flea beetles did not differ in broccoli adjacent to diverse versus simple trap crops, or in the trap-crops themselves. This suggests that plant protection resulted from a change in pest behavior rather than abundance. Our study revealed that increasing biodiversity of trap-crop plantings might be an effective means to enhance the success of the approach in many systems.