The influence of organic transition systems on beneficial ground-dwelling arthropods and predation of insects and weed seeds

Abstract

AbstractThe influence of farm management practices on ground-dwelling natural enemy communities and predation of insects and weed seeds was investigated over the first 2 years of the transition from conventional to organic production. Three transition strategies were selected that differed in their management and input intensities, and were characteristic of pasture/ley systems (low intensity), cash grain systems (intermediate intensity), and vegetable production (high intensity). Beneficial arthropods (insectivores and granivores) were monitored using pitfall (arthropod activity) and quadrat (arthropod density) samples. The frequency of predation on restrained larvae ofGalleria mellonellaand the species observed feeding were recorded. Weekly removal rates of weed seeds representative of abundant species at our site were monitored over a 3-week period during fall. Management intensity affected the activity and abundance of biological control agents. In year two of the transition, biological control agent densities were higher in the low-intensity treatment than in the other two treatments, but activity of insectivores and granivores was reduced in this treatment relative to the higher intensity systems. The patterns in the abundances of biological control agents may be explained by habitat stability within the different cropping systems. Quadrat samples were strongly correlated with the insectivory index, although pitfall samples were not. Insectivory rates were highest (>80% ofG. mellonellalarvae) in the low-intensity treatment. Predation patterns over a 17-h period differed substantially among the management treatments, indicating behaviorally distinct insectivore communities. Seed removal was also highest in the low-intensity treatment. We conclude that low-intensity cropping systems are most favorable to the abundance and function of beneficial ground-dwelling arthropod communities (insectivores and granivores) during the transition process.