Predators of the rosy apple aphid, Dysaphis plantaginea (Pass.), in Asturian (NW Spain) apple orchards

Alternative strategies to the common practice of spraying with insecticide in order to control the rosy apple aphid Dysaphis plantaginea (Pass.) (Homoptera: Aphididae) are required. Biological control by natural enemies is a possible tool. In Asturies, despite the tradition of growing local cider apple trees, there are no studies about the community of D. plantaginea predators and their impact on these aphid populations. The aim of this work is to fill this gap. The presence of beneficials in the D. plantaginea colonies was important reaching in some surveys to 100 % of the infested terminals. The three most abundant predators were Episyrphus balteatus (DeGeer) (Diptera: Syrphidae), Adalia bipunctata (L.) (Coleoptera: Coccinellidae) and Aphidoletes aphidimyza (Rond.) (Diptera: Cecidomyiidae). When the first colonies of D. plantaginea developed in April, only syrphids and coccinellids were present. Syrphid eggs or larvae occurred in more than 80 % of the colonies, coccinellids were less frequent but their population increasing progressively. Cecidomyiids appeared in mid-May and their number increased quickly. Other Coccinellidae and Syrphidae, as well as Anthocoridae and Miridae (Heteroptera), Cantharidae (Coleoptera), Forficulidae (Dermaptera) and Chrysopidae (Neuroptera) were also observed preying on D. plantaginea colonies. Although these predators are considered to play an important role in the regulation of aphid populations, they did not prevent D. plantaginea damage that affected up to 37 % of the terminals in one orchard and up to 54 % in another. Some possible causes for this ineffectiveness are discussed.