Effect of Brassica chinensis intercropping with Glycine max or Colocasia esculenta on Spodoptera litura and natural enemy predatory diversity in protected vegetable fields

Appropriate intercropping systems could promote crop yield and quality, alleviate disease and insect pest damages, enhance multiple crop index and facilitate efficient utilization of sunlight, heat, water, air, fertilizer, etc. An experiment was therefore conducted in a protected horticulture park in Pudong District, Shanghai Municipality (with location coordinates of 121.70°E, 31.19°N) to determine the effects of intercropped host plants soybeans (Glycine max) and taros (Colocasia esculenta) in Brassica chinensis field on Spodoptera litura vegetable insect-pest and structural characteristics of natural predatory enemies. Protected vegetable fields with row-intercropped soybeans or taros were the main treatments and protected mono-cultured B. chinensis field was the control (CK) in the experiment. Trapped individual larvae and eggs in soybeans and taros were counted and natural predatory enemy community structure characteristics systematical analyzed. The results indicated that during the July-to-September investigation period, 100 plants of soybeans and taros trapped 1 098.84±107.50 and 1 260.78±126.16 larvae, respectively. 100 plants of soybeans and taros also trapped 17.45±1.31 and 20.76±1.81 individual eggs, respectively. Compared with CK, S. litura population in protected vegetable fields with intercropped soybeans and taros decreased by 37.83% and 45.89%, respectively. There were 31 natural predatory enemy species belonging to 21 families and 5 orders in protected vegetable fields with intercropped soybeans. Also 32 natural predatory enemy species belonging to 21 families and 5 orders were in protected vegetable fields with intercropped taros. The CK fields had 26 natural predatory enemy species belonging to 19 families and 5 orders. The dominant natural predatory enemy species were Lycosa pseudoamulata and Erigonidium graminicolum in CK fields and L. pseudoamulata, E. graminicolum and Pirata subpiraticus in protected vegetable fields with intercropped soybeans and taros. The individual number per-100-plant, richness and diversity index of natural predatory enemies in protected vegetable fields with intercropped soybeans were 91.22±4.91, 29.74±0.30 and 4.53±0.03, respectively, representing increases of 58.70%, 25.27% and 10.60% over CK. Also the individual number per-100-plant, richness and diversity index of natural predatory enemies in protected vegetable fields with intercropped taros were 92.09±5.03, 29.96±0.35 and 4.54±0.03, respectively, representing increases of 60.21%, 26.19% and 11.00% over CK. Based on the study, vegetable intercropping with soybeans or taros was a potential mode of controlling S. litura and facilitating the effect of natural predatory enemies on insect pests. These intercropping systems were not only beneficial to arthropod community diversity and stability, but were also an environmental friendly agro-ecosystem.