title: Diet of generalist predators reflects effects of cropping period and farming system on extra- and intraguild prey.
abstract: The suppression of agricultural pests by natural enemies, including generalist arthropod predators, is an economically important regulating ecosystem service. Besides pests, generalist predators may also consume non-pest extraguild and intraguild prey, which can affect their impact on pest populations. This may either reduce the impact of generalist predators on pest populations, because they are diverted from pest predation, or increase it, as it helps them survive periods of low pest availability. However, the availability of pest prey and alternative, non-pest prey can vary over the crop growing season and between farming systems, potentially affecting predator-prey interactions and the levels of biological control. We have limited information about how farming systems and environmental variation over the crop growing season influence predator diets. This limits our ability to predict the importance of generalist predators as natural enemies of agricultural pests. Here we utilize molecular gut content analyses to assess detection frequencies of extra- and intraguild prey DNA in generalist predator communities in replicated organically and conventionally managed cereal fields at two key periods of the cropping season for aphid biological control. This is done in order to understand how farming system, crop season, prey availability and predator community composition determine the composition of predator diets. Aphid pests and decomposers (springtails) were equally important prey for generalist predators early in the growing season. Later in the season, the importance of aphid prey increased with increasing aphid densities while springtail predation rates were positively correlated to abundance of this prey at both early and late crop growth stages. Intraguild predation was unidirectional: carabids fed on spiders, whereas spiders rarely fed on carabids. Carabids had higher detection frequencies for the two most common spider families in organically compared to conventionally managed fields. Our study documents that predation by generalist predator communities on aphid pests increases with pest numbers independently of their generally widespread consumption of alternative, non-pest prey. Therefore, conservation strategies in agricultural fields could promote biological control services by promoting high levels of alternative non-pest prey for generalist predator communities.
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, PO Box 7044, 75007, Uppsala, Sweden.
authors.forename: Eve
authors.initials: E
authors.lastname: Roubinet
authors.affiliation: Department of Biology, Biodiversity and Conservation Science, Lund University, Sölvegatan 37, 22362, Lund, Sweden.|Department of Ecology, Brandenburg University of Technology Cottbus-Senftenberg, Konrad-Wachsmann-Allee 6, 03046, Cottbus, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Birkhofer
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, PO Box 7044, 75007, Uppsala, Sweden.
authors.forename: Gerard
authors.initials: G
authors.lastname: Malsher
authors.affiliation: Mountain Agriculture Research Unit, Institute of Ecology, University of Innsbruck, Innsbruck, Austria.
authors.forename: Karin
authors.initials: K
authors.lastname: Staudacher
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, PO Box 7044, 75007, Uppsala, Sweden.
authors.forename: Barbara
authors.initials: B
authors.lastname: Ekbom
authors.affiliation: Mountain Agriculture Research Unit, Institute of Ecology, University of Innsbruck, Innsbruck, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Traugott
authors.affiliation: Department of Ecology, Swedish University of Agricultural Sciences, PO Box 7044, 75007, Uppsala, Sweden.
authors.forename: Mattias
authors.initials: M
authors.lastname: Jonsson
mesh_terms: D000818:Animals; D000069599:Crop Production / Q000379:methods*; D004032:Diet; D020387:Food Chain; D001467:Hordeum / Q000254:growth & development; D007313:Insecta / Q000502:physiology; D011235:Predatory Behavior; D013112:Spiders / Q000502:physiology; D013548:Sweden
keywords: Araneae; Carabidae; aphids; biological control; intraguild predation; molecular gut content analyses; organic farming