Demographic and quantitative food web analysis of Sitobion avenae and its natural enemies.
Objectives: The English green aphid, Sitobion avenae (Fabricius), is one of the most important pests of winter wheat in China. To clarify the occurring of S. avenae and its natural enemies in wheat-oil-seed rape and wheat-garlic intercropping patterns, so as to provide basis for the sustainable utilization of natural enemies and ecological control of wheat aphids. Methods: The occurrence of this pest, and a quantitative food web analysis of it and its natural enemies, were conducted in wheat-oil-seed rape and wheat-garlic intercropping regimes. Results: The results show that the densities of S. avenae apterae were significantly lower in wheat-oil-seed rape intercropped fields and wheat-garlic intercropped fields than in wheat monocultures during almost the entire wheat filling stage. There were higher population densities of ladybeetles in wheat-oil-seed rape intercropped fields. Population densities of aphid parasitoids were significantly higher in wheat-oil-seed rape intercropping systems during the wheat earring and flowering stages. In wheat-garlic intercropped fields, the number of S. avenae alatae was higher, but no adverse effects were detected on the population densities of ladybeetles and aphid parasitoids. The quantitative food web analysis showed that, although the control effectiveness of green lacewings and syrphid flies differed under the three different planting regimes, that of ladybeetles and parasitoids was almost the same. Conclusion: Wheat-oil-seed rape and wheat-garlic intercropping could increase the population density of dominate species of natural enemies, and reduce the population density of S. avenae in agroecosystems.