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Generalist predators in organically and conventionally managed grass-clover fields: implications for conservation biological control

Birkhofer , K; Fließbach , A; Wise , DH and Scheu , S (2008) Generalist predators in organically and conventionally managed grass-clover fields: implications for conservation biological control. Annals of Applied Biology, 153, pp. 271-280.

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Organically managed agroecosystems rely in part on biological control to prevent pest outbreaks. Generalist predators (Araneae, Carabidae and Staphylinidae) are a major component of the natural enemy community in agroecosystems.
We assessed the seasonal dynamics of major generalist predator groups in conventionally and organically managed grass–clover fields that primarily differed by fertilisation strategy. We further established an experiment, manipulating the abundant wolf spider genus Pardosa, to identify the importance of these predators for herbivore suppression in the same system and growth period. Organic management significantly enhanced ground-active spider numbers early and late in the growing season, with potentially positive effects of plant cover and non-pest decomposer prey. However, enhancing spider numbers in the field experiment did not improve biological control in organically managed grass–clover fields. Similar to the survey results, reduced densities of Pardosa had no short-term effect on any prey taxa; however, spider guild structure changed in response to Pardosa manipulation. In the presence of fewer Pardosa, other ground-running spiders were more abundant;therefore, their impact on herbivore numbers may have been elevated, possibly cancelling increases in herbivore numbers because of reduced predation by Pardosa. Our results indicate positive effects of organic farming on spider activity density; however, our survey data and the predator manipulation experiment failed to find evidence that ground-running spiders reduced herbivore numbers. We therefore suggest that a positive impact of organic fertilisers on wolf spiders in grass–clover agroecosystems may not necessarily improve biological control when compared with conventional farming.

EPrint Type:Journal paper
Keywords:Araneae; Carabidae; DOK trial; farming system; intraguild interactions; natural enemies; organic farming.
Subjects: Soil > Soil quality > Soil biology
Environmental aspects > Biodiversity and ecosystem services
Research affiliation: Switzerland > FiBL - Research Institute of Organic Agriculture Switzerland > Soil Sciences
Deposited By: Birkhofer, Dipl. Biol. Klaus
ID Code:19615
Deposited On:04 Nov 2011 19:00
Last Modified:20 Dec 2011 10:48
Document Language:English
Refereed:Peer-reviewed and accepted

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