Do hedgerows influence the natural biological control of woolly apple aphids in orchards?

The provision of refuges for natural enemies could be a key aspect for the management of the woolly apple aphid [Eriosoma lanigerum (Hausmann, 1802)] (Hemiptera: Aphididae) in apple orchards. The present study assesses the effects of Pyracantha coccinea (Rosaceae) (firethorn) adjacent to apple orchards as this extra-orchard habitat would positively affect the abundance of natural enemies and control of E. lanigerum. Abundances were evaluated for the pest, the parasitoid, Aphelinus mali (Haldeman, 1851) (Hymenoptera: Aphelinidae) (during two seasons) and generalist predators (only during the second season). The assessments were conducted at different distances from P. coccinea located at the edge of the apple orchards. Additionally, parasitism rates by A. mali were examined using a categorical and two quantitative methods. Results indicate that P. coccinea hedges promoted an early colonization by A. mali in apple orchards especially during the first season. However, parasitism rates by A. mali were not affected at the beginning of the season, but as the season progressed, the rates increased on the apple trees in comparison with the hedges. Additionally, during the second season, the interaction between certain natural enemies had a stronger effect on the population growth rates of E. lanigerum in orchards with P. coccinea compared to control orchards. Based on these results, we conclude that P. coccinea hedges may promote the early colonization by A. mali in the orchards and have a positive effect on the abundance of spiders, but had no effect on coccinelid, carabids, earwigs and syrphids.