Effects of organic and conventional farming of triticale cereals on biological pest control

Background/Question/Methods

Ecosystem services like pollination and pest control are essential benefits for farmers. In cereals aphids are one of the main pest species, as they harm the crops directly when abundances are high or indirectly by distributing viruses. It is assumed that organic management of cereal fields enhances biological pest control of aphids, as potential flower resources can attract and support predators. We therefore compared 15 triticale fields, which were organically managed with 15 fields which were conventionally managed and recorded plants, pollinators, aphids and aphid predators throughout the growing season. As damage of aphid pests is occasionally high in conventional fields, five of the 15 conventional fields were sprayed with “aphid specific” insecticides. We compared the aphid and predator abundances through the season to detect possible time-delayed responses of insecticide spraying.

Results/Conclusions

In total we identified in organic fields 114 vascular plant species and in conventional fields 55 species. Similarly pollinator species richness and abundances were significantly higher in organic compared to conventional fields. The predator-prey ratio was 21 times higher in organic fields, as aphid predators were more abundant and aphids less abundant in organic compared to conventional fields. In total we recorded 8835 aphids in the 30 triticale fields, thereby 7296 individuals occurred on conventional and only 1539 individuals occurred on organic fields. Comparing the five conventional fields, which were sprayed against aphids with the ten conventional fields with no spraying early in the year, the seasonal patterns showed that the insecticide spraying had only a short time effect, reducing the aphids at the beginning of the season, but resulting in enhanced abundance later in the season. Our data indicate that spraying had a long-term negative effect on aphid predators as their abundances remained low throughout the season. In conclusion we suggest that the spraying of insecticides should not be applied before critical pest thresholds are reached to make use of cost-free and efficient biological pest control.