Abstract
One of the most important services provided by biodiversity is thought to be the biological control of pests in agricultural landscapes, including aphids on cereals. The food webs potentially contributing to biological control of aphids primarily consist of polyphagous predators, parasitoids and pathogens. The problems of aphid pests have increased greatly since the 1970-ies, possibly as an effect of agricultural intensification, which is thought to have reduced diversity and abundance of these predators and parasites and consequently their biocontrol potential. The main objective of this study was to test this by measuring this potential for bio- logical control of aphids, and relate it to agricultural intensification and predator abundance. We selected 30 farms distributed along agricultural intensification gradients, based on the amount of fertilizers applied per hectare. Estimates of ground-living predator den- sity were obtained using pitfall trapping over a one-week period. Traps were placed inside the cereal fields, 10 m from the margin, in 2 replicates per field. Predation risk due to ground-living predators (biocontrol potential) was estimated by monitoring removal of aphids glued to labels. This was done in the same fields, in the immediate vicinity of the traps, over a period of 2 days. The propor- tion of aphids eaten per unit time was the response variable. We present the correlations between intensity of agricultural exploita- tion, predator abundance and biocontrol potential. The outcomes are not straightforward in that intensification begets a reduction in predator density and biocontrol potential. We discuss the potential confounding issues that might have affected our results.
Highlights
Intensive production of cereals comprises about 21% of European land cover (33.81 millions of ha), corresponding to one third of the total European area devoted to agriculture (European Environmental Agency, 2000)
The species loss in European agricultural landscapes has been the result of changes in the food webs induced by structural habitat modifications or changes in the supply and diversity of the species’ resource base
One of the most important services provided by biodiversity is the biological control of pests in agricultural landscapes (Weisser & Siemann, 2004)
Summary
Intensive production of cereals comprises about 21% of European land cover (33.81 millions of ha), corresponding to one third of the total European area devoted to agriculture (European Environmental Agency, 2000). Over the last 50 years, farmland in western European countries has experienced dramatic changes, mainly through the intensification of farming techniques (Siriwardena et al, 2000; Robinson & Sutherland, 2002) associated with the Common Agricultural Policy (CAP). This has entailed a loss of biodiversity judged to be similar to that expected from climate change. One of the most important services provided by biodiversity is the biological control of pests in agricultural landscapes (Weisser & Siemann, 2004) In this context, abundance of insect biocontrol agents, rather than their species diversity plays a primary role: more individuals of natural enemies can eat more individuals of insect pests. A decline in the total number of natural enemy individuals negatively affects pest biocontrol
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