Submitted to: Renewable Agriculture and Food Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/19/2005
Publication Date: 11/15/2006
Citation: Lundgren, J.G., Shaw, J.T., Zaborski, E.R., Eastman, C.E. 2006. The influence of organic transition systems on beneficial ground-dwelling arthropods and biological control of insects and weed seeds. Renewable Agriculture and Food Systems. 21(4):227-237. Interpretive Summary: Transitioning to organic production is accomplished using different strategies by different farmers. These different strategies have important implications for beneficial arthropod communities and their ability to suppress insect and weed seed banks. Here, we evaluate the impacts of three transition systems on biological control potential over the first two years of the transition process. We monitored natural enemy communities using pitfall and quadrat samples, and examine predation of insect larvae and weed seeds in the different systems. We found that less disturbance, characteristic of pasture systems is most favorable to natural enemy communities.
Technical Abstract: The influence of farm management practices on ground-dwelling natural enemy communities and predation of insects and weed seeds was investigated over the first two years of the transition from conventional to organic production. Three transition strategies selected that varied 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 of Galleria mellonella and the species observed feeding were recorded. Weekly removal rates of weed seeds representative of abundant species at our site were monitored over a three-week period during fall. Management intensity affected the activity and abundance of natural enemy communities. In year two of the transition, natural enemy densities were higher in the low-intensity treatment than in the other two treatments, but activity of natural enemies was reduced in this treatment relative to the higher-intensity systems. The patterns in the abundances of natural enemies 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% of G. mellonella larvae) 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.