Effects of Organic Management on Predator Densities of Myzus persicae (Sulzer) During Transition to Organic Agriculture in Peach Fields in China

We studied the effects of organic management (OM) on densities of six predator species of green peach aphid (GPA), three coccinellid predators (Propylea japonica, Harmonia axyridis, Coccinella septempunctata), and three non-coccinellid predators (Chrysoperla sinica, Epistrophc baltcata, and Misumenops tricuspidatus) in five OM peach fields, compared and paired with five conventional management (CM) fields from the first year of OM in 2004–2009. Coccinellid and non-coccinellid predator densities were significantly higher on several sampling dates in OM fields than in CM fields. Coccinellid predator density was significantly lower in the first two years of OM than in the last three years in the OM fields. The density of non-coccinellid predators in the fourth year of OM was much greater than during the first year of OM, and there was a significant increase by the sixth year of OM compared to the first two years of OM. The leaf density index of GPA was significantly lower in the fifth and sixth year of OM than the first three years of OM in the OM peach fields. Our study suggests organic management can resume and increase predator densities of green peach aphid during transition to organic agriculture in peach fields.