Reduced crop damage by self-regulation of aphids in an ecologically enriched, insecticide-free apple orchard

Enhancing natural enemies for pest management in agriculture is an expanding approach offering new opportunities for pest control and the potential to reduce insecticide use. Numerous studies in a variety of cropping systems clearly have shown that adequate measures can benefit natural enemies. However, although carry-over effects from an increase in natural enemies and a subsequent decrease in pest populations leading to a reduction in crop damage are always assumed, they are rarely proven. We established an insecticide-free apple orchard optimized for the self-regulation of pests by supporting natural enemies with shelter, nectar, alternative prey/hosts, and pollen. For six growing seasons, we focused on the control of the major apple pest Dysaphis plantaginea. While fruit damage after the second fruit drop was not affected by aphidophagous insect guilds, it was negatively related to spider abundance in the previous autumn, when aphids immigrate back to the orchard to establish the next generation. In detail, we found that an increase in spider web area reduced the number of aphid fundatrices in spring and subsequently fruit damage. Our findings indicate the rarely proven carry-over effect of enhanced natural enemies on decreased crop damage and we show for the first time, how the rosy apple aphid can be managed without the use of insecticides