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

Birkhofer, Klaus LU ; Fließbach, Andreas; Wise, David H. and Scheu, Stefan (2008) In Annals of Applied Biology 153(2). p.271-280
Abstract
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... (More)
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. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Araneae, Carabidae, DOK trial, farming system, intraguild interactions, natural enemies, organic farming
in
Annals of Applied Biology
volume
153
issue
2
pages
271 - 280
publisher
Wiley-Blackwell
external identifiers
  • scopus:53249113475
ISSN
0003-4746
DOI
10.1111/j.1744-7348.2008.00257.x
language
English
LU publication?
yes
id
b15e475c-db8e-4934-8dbe-f4cc5cbfc4ca (old id 2440466)
alternative location
http://www.scopus.com/inward/record.url?eid=2-s2.0-53249113475&partnerID=40&md5=f84badafcdbf8948a71ae93c73d69df5
date added to LUP
2012-06-18 16:42:24
date last changed
2017-08-20 03:32:25
@article{b15e475c-db8e-4934-8dbe-f4cc5cbfc4ca,
  abstract     = {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.},
  author       = {Birkhofer, Klaus and Fließbach, Andreas and Wise, David H. and Scheu, Stefan},
  issn         = {0003-4746},
  keyword      = {Araneae,Carabidae,DOK trial,farming system,intraguild interactions,natural enemies,organic farming},
  language     = {eng},
  number       = {2},
  pages        = {271--280},
  publisher    = {Wiley-Blackwell},
  series       = {Annals of Applied Biology},
  title        = {Generalist predators in organically and conventionally managed grass-clover fields: implications for conservation biological control},
  url          = {http://dx.doi.org/10.1111/j.1744-7348.2008.00257.x},
  volume       = {153},
  year         = {2008},
}