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Biodiversity vs. biocontrol: positive and negative effects of alternative prey on control of slugs by carabid beetles

Published online by Cambridge University Press:  24 July 2007

W.O.C. Symondson*
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
S. Cesarini
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
P.W. Dodd
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
G.L. Harper
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
M.W. Bruford
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
D.M. Glen
Affiliation:
IACR-Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol, BS41 9AF, UK
C.W. Wiltshire
Affiliation:
Arion Ecology, The Brambles, Stinchcombe Hill, Dursley, Gloucestershire, GL11 6AQ, UK
J.D. Harwood
Affiliation:
Cardiff School of Biosciences, Cardiff University, PO Box 915, Cardiff CF10 3TL, UK
*
*Fax: +44 (0)29 20 874 305 E-mail: Symondson@Cardiff.ac.uk

Abstract

Environment-friendly farming techniques seek to increase invertebrate biodiversity in part with the intention of encouraging greater numbers of predators that will help to control crop pests. However, in theory, this effect may be negated if the availability of a greater abundance and diversity of alternative prey diverts predators away from feeding on pests. The hypothesis that access to alternative prey can lead to reduced pest suppression under semi-field conditions was tested. Alternative prey type and diversity were manipulated in 70 mesocosms over 7+ weeks in the presence of the carabid Pterostichus melanarius (Illiger), a known predator of slugs, and reproducing populations of the slug Deroceras reticulatum (Müller). Significantly fewer slugs survived where no alternative prey were provided. Maximum slug numbers and biomass were found in treatments containing either carabids plus a high diversity of alternative prey (many species of earthworm and three of Diptera larvae) or a single additional prey (blowfly larvae, Calliphora vomitoria Linnaeus). In these treatments slug numbers and biomass were as high as in plots lacking predators. The effects of alternative prey were taxon-specific. Alternative prey strongly affected carabid fitness in terms of biomass and egg load. The fittest predators (those with access to high alternative prey diversity or C. vomitoria larvae) reduced slug numbers the least. The mean individual slug weights were greater in treatments with alternative prey than where no alternative prey were provided to the carabids. These results suggest that pests may survive and reproduce more rapidly in patches where predators have access to alternative prey.

Information

Type
Research Article
Copyright
Copyright © Cambridge University Press 2006

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