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Generalist predators in agroecosystems may immigrate into the crop fields from the surrounding environment or may be agrobiont species that maintain stable populations in crop fields but are scarce in natural habitats. This study compared pest consumption of two main spider groups in wheat fields of a semidesert agroecosystem of Israel, the immigrant spiders of the family Theridiidae (Enoplognatha spp.) and the agrobiont family Linyphiidae, to identify their potential role in biological control. The consumption of pest (aphids and Hessian flies) and non-pest arthropods (Collembola) was examined using PCR-based molecular gut content analysis. We describe the development of one new set of primer pairs targeting Hessian flies. We also used existing aphid-and collembolan-specific primers to test the hypotheses that agrobiont spiders are more likely to consume the most common prey species, while immigrant species will utilize pest prey more frequently than agrobionts. Our results indicated that a significantly higher proportion of immigrating Enoplognatha consumed aphids as compared to the agrobiont linyphiids, which mostly consumed collembolans. The results suggest that Enoplognatha have some degree of prey selection toward the crop pests (aphids). We therefore conclude that immigrant spiders may be particularly important biological control agents in the semi-arid wheat agroecosystem in Israel. (C) 2012 Elsevier Inc. All rights reserved.