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Landscape and farm management influence generalist predators

Effects on condition, abundance and biological control

Östman, Örjan (2002). Landscape and farm management influence generalist predators. Diss. (sammanfattning/summary) Uppsala : Sveriges lantbruksuniv., Acta Universitatis agriculturae Sueciae. Agraria, 1401-6249 ; 363
ISBN 91-576-6187-1
[Doctoral thesis]

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Abstract

Chemical pest control is currently the dominant form of pest management against insect pests in agroecosystems, but has negative side effects. Biological control by specialist predators has been successful in greenhouses, but has not been successfully applied in agroecosystems. Generalist predators have features constraining them as control agents, but have one advantage: they can survive when pests are absent by feeding on alternative prey. In this thesis I have studied the influence of landscape structures and farm management on generalist predators and their predation on an aphid pest on cereals, Rhopalosiphum padi. In accordance with theoretical predictions, predation on establishing aphids in spring was more important for the total aphid attack than predation during the aphid population growth phase. Predation on establishing aphids was higher on organic than conventional farms and highest in landscapes with abundant field margins and perennial crops. Predation during the population growth phase was, surprisingly, highest in simple landscapes, with no differences between organic and conventional farms. The presence of alternative prey can result in decreasing predation of generalist predators on pests, and I show that this effect is scale-dependent. On a field scale, generalist predators were aggregated at high prey densities, and predator abundance was more important for predation on aphids than alternative prey abundance. Thus, the effect of alternative prey was larger on the generalist predator abundance than on the predators' diet. However, higher alternative prey abundance in complex landscapes may still have resulted in the observed lower predation rates on aphids in these landscapes during aphid population growth. Condition of generalist predators, which often is food-limited, was better on organic farms and in landscapes with abundant field margins in a non-aphid year. Possibly because of an aphid outbreak, condition changed asynchronously between farms over three study years. The temporal and spatial environmental variation affected the condition of different species differently, which can be explained by the species’ diet and habitat selectivity. This thesis provides further evidence for earlier suggestions that more field margins and perennial crops in relation to annual crops increase alternative prey abundance and overwintering sites for the generalist predators and thereby their abundance, which can enhance biological control of cereal aphids.

Authors/Creators:Östman, Örjan
Title:Landscape and farm management influence generalist predators
Subtitle:Effects on condition, abundance and biological control
Year of publishing :April 2002
Volume:363
Number of Pages:33
Papers/manuscripts:
NumberReferences
ALLI. Östman, Ö. Ekbom, B. & Bengtsson, J. 2001. Landscape heterogeneity and farming practice influence biological control. Basic and Applied Ecology 2: 365-371. II. Östman, Ö. The relative effects of natural enemy abundance and alternative prey abundance on aphid predation rates in ephemeral agricultural habitats. (Submitted). III. Östman, Ö. & Ives, A.R. Scale-dependent interactions between two prey through a shared predator. (Submitted). IV. Östman, Ö. Ekbom, B. Bengtsson, J. & Weibull, A. 2001. Landscape complexity and farming practice influence the condition of polyphagous carabid beetles. Ecological Applications 11: 480-488. V. Östman, Ö. Spatial and temporal variation in condition and fecundity of two carabid species in agricultural landscapes in Sweden. (Manuscript).
Place of Publication:Uppsala
ISBN for printed version:91-576-6187-1
ISSN:1401-6249
Language:English
Publication Type:Doctoral thesis
Full Text Status:Public
Agris subject categories.:H Protection of plants and stored products > H10 Pests of plants
Subjects:Not in use, please see Agris categories
Agrovoc terms:pest control, alternative methods, biological control, biological control agents, rhopalosiphum padi, pest insects, cereal crops, natural enemies, carabidae, nabidae
Keywords:bird cherry-oat aphid, Carabidae, Nabidae, fitness, natural enemies, patch choice, selectivity, spatial-temporal variation.
ID Code:207
Department:(NL, NJ) > Institutionen för ekologi och växtproduktionslära (fr.o.m. 990101)
Deposited By: Örjan Östman
Deposited On:02 Apr 2003 00:00
Metadata Last Modified:02 Dec 2014 10:02

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