Effects of position within wheat field and adjacent habitats on the density and diversity of cereal aphids and their natural enemies
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The spatial structure of agricultural land- scapes can have a strong impact on the distribution and diversity of insects. Here we studied the effects of within-field position (edge or center) as well as adjacent habitats on the community structure of the natural enemies of cereal aphids. Twelve agricultural sites were included in the study, with two spring wheat fields selected for each site (one adjacent to an alfalfa field, the other adjacent to a corn field). We sampled two rows per field (1 and 20 m from the edge) using pitfall trapping for ground-dwelling predators, sweep netting for leaf- dwelling predators and hand collecting of aphid mummies for parasitoids. Adjacent alfalfa areas, as opposed to corn fields, can significantly increase the abundance and diversity of leaf-dwelling predators and parasitoids near the field edges. Abundance and diver- sity were found significantly higher near the edges than in the centers of fields adjacent to alfalfa areas. In contrast, no significant differences were found between edges and centers of fields adjacent to corn fields. Of the fifteen most abundant species, Aphidius avenae (Hali- day), A. gifuensis (Ashmead), Hippodamia variegata (Goeze) and Chrysopa sinica (Tjeder) were significantly more abundant near the edge than in the center. Being adjacent to alfalfa habitats could enhance parasitism and predator/prey ratios of leaf-dwelling predators at the edges, but has no effects on ground-dwelling predators. In conclusion, the effect of within-field position and adjacent habitats on natural enemies of agricultural pests was species specific. This should be considered for designing efficient plans of biological control.
- RESEARCH: Hui C