Contrasting effects of codling moth exclusion netting on the natural control of the rosy apple aphid

Abstract: Exclusion netting is developing in Southern France against Cydia pomonella, a major pest of apple. Most insecticides and therefore side-effects on natural enemies (NE) are avoided in netted orchards. Conversely, nets can also exclude some NE and/or modify their access to prey in the tree canopy. The effect of nets on the beneficial complex associated to the rosy apple aphid (RAA) was studied in experimental and commercial orchards in 2009 and 2012 in South-Eastern France. RAA infestation was reduced or increased by nets depending on the orchard type (experimental vs. commercial) and the site and study year. NE were not (Syrphidae) to strongly (Coccinellidae) affected by nets in Avignon sites whereas the abundance of all NE groups was reduced under nets in Valence site. Such discrepancies are probably due to entangled processes related to site climate, type of orchard and/or the role of ants as commensalists of aphids. This outlines the complexity of multi-pest approaches and biocontrol processes as affected by cultural practices.