Natural regulation of the rosy apple aphid (Dysaphis plantaginea) in organic apple orchards

Abstract: Rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), is the most detrimental aphid species in European organic apple orchards. This study aimed to evaluate the natural regulation of D. plantaginea and the effect of installing hail nets on this regulation. The study was carried out during spring 2008 in one experimental apple orchard without pesticide and four organic commercial apple orchards located in southern France. The density and the diversity of natural enemies observed in the experimental orchard were higher than those in the organic orchards. The colonies of D. plantaginea were exploited by a multispecific guild of natural enemies. Hoverflies, lady beetles and earwigs were the most abundant groups. Hoverflies tended to arrive first, followed by lady beetles and earwigs. A high level of aphid infestation was observed in two organic orchards, presumably related to a low level of natural enemies and to a high level of ants. Regarding the effect of hail nets, the study revealed a positive influence of the hail nets on regulation by earwigs but a negative influence on the presence of other natural enemies especially lady beetles. To sum up, this field study indicated that the population dynamic of D. plantaginea was strongly affected by natural enemies, but not sufficiently to maintain it under the tolerance threshold. So, new management practices aiming at enhancing this natural regulation need to be found.