The relative occurrence and seasonal abundance of aphidophagous predators (Insecta and Arachnida) were determined inalfalfa fields at two locations in the northeast Iberian Peninsula, using D-Vac and sweep-net sampling techniques. Among theinsects, Heteroptera, Dermaptera, Neuroptera, Coleoptera and Diptera were found. The relative abundance of predators was similarat the two locations. Polyphagous predators were much more abundant than aphid specific species. Heteroptera were the most abundantorder of insect predators: members of the Nabidae, Anthocoridae and Miridae were very common. Coleoptera were also abundant,represented mainly by the family Staphylinidae. Coccinellidae were less abundant and their occurrence coincided withmaximum aphid presence. There was a low occurrence of other aphid-specific predators, i.e. Diptera: Syrphidae and Neuroptera:Chrysopidae. Arachnida varied between localities (from 35% to 65%). Over a five-year period, numerical responses by Orius spp.,Nabis provencalis and Coccinellidae to aphids were found using polynomial regression models; however the abundance of predatorswas weakly explained by aphid abundance. Alfalfa, maize and winter cereals share similar aphid predator groups and these cropspartially coincide in time, enabling the movement of predators among crops. The persistence of several predatory groups (Anthocoridae,Nabidae, Staphylinidae, Araneae) during most of the season suggests that alfalfa plays a major role as a reservoir of aphidpredators.
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