Quantifying the impact of polyphagous invertebrate predators in controlling cereal pests and in preventing quantity and quality reductions.

Abstract

Exclusion barriers were used to quantify the effect of polyphagous invertebrate predators on cereal aphids and orange wheat blossom midge within the LINK Integrated Farming System Project. Exclusion experiments demonstrated that polyphagous predators can reduce a late aphid infestation by up to 31 %. A greater impact was found when the aphid population developed more slowly. However, the polyphagous predators did not reduce the number of tillers infested or prevent the recommended spary threshold being reached. Aphid predation helped to preserve grain protein to a small extent (0.4%) in one field but effects may be larger if aphids infest the crop earlier in the season. Polyphagous predators did not feed on orange wheat blossom midge eggs on the ear but reduced by 22% the number of larvae which were able to return to the soil after leaving the ear. Sowing date was shown to govern the time over which a crop may be susceptible to aphids and midge. Late drilling made the crop more susceptible to a late aphid infestation but reduced by 50% the number of midge per ear because the crop was at a less susceptible stage during oviposition. Consequently the number of midge returning to the soil was lower by 80%.