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. 2005 Jan 22;272(1559):203-10.
doi: 10.1098/rspb.2004.2902.

The landscape context of cereal aphid-parasitoid interactions

Carsten Thies  1 , Indra Roschewitz, Teja Tscharntke
Affiliations

The landscape context of cereal aphid-parasitoid interactions

Carsten Thies et al. Proc Biol Sci. .

Abstract

Analyses at multiple spatial scales may show how important ecosystem services such as biological control are determined by processes acting on the landscape scale. We examined cereal aphid-parasitoid interactions in wheat fields in agricultural landscapes differing in structural complexity (32-100% arable land). Complex landscapes were associated with increased aphid mortality resulting from parasitism, but also with higher aphid colonization, thereby counterbalancing possible biological control by parasitoids and lastly resulting in similar aphid densities across landscapes. Thus, undisturbed perennial habitats appeared to enhance both pests and natural enemies. Analyses at multiple spatial scales (landscape sectors of 0.5-6 km diameter) showed that correlations between parasitism and percentage of arable land were significant at scales of 0.5-2 km, whereas aphid densities responded to percentage of arable land at scales of 1-6 km diameter. Hence, the higher trophic level populations appeared to be determined by smaller landscape sectors owing to dispersal limitation, showing the 'functional spatial scale' for species-specific landscape management.

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Figures

Figure 1
Figure 1
Dependence of cereal aphid densities (a–c) and percentage of parasitism (d–f) on the percentage of arable land within circular landscape sectors of 1 km diameter in three consecutive years: (a,d) 2001; (b,e) 2002; (c,f) 2003. Open quadrats and solid lines: wheat flowering stage in June (after the main period of aphid colonization of the fields); filled points and dashed lines: wheat milk-ripening stage in July (after the main period of aphid reproduction in the fields). Regression lines are shown for descriptive purposes. See table 2 for statistics. Note the logarithmic scale for aphid densities.
Figure 2
Figure 2
Relation of aphid population growth (the proportion of aphid density at wheat milk ripening (dwmr) and aphid density at wheat flowering (dwfl)=dwmr/dwfl) to percentage of parasitism. Spearman's rank correlation: p<0.001, n=40, rS=−0.547.
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