Relationship between landscape composition and the abundance of aphids and their natural enemies in crop fields
We investigated, over the course of two years, the importance of landscape context on the abundance of aphids and their natural carabid enemies, which may help to develop effective strategies for reduction of aphid outbreaks in agricultural landscapes. This was undertaken in 12 wheat fields and in 12 maize fields each year in an agricultural landscape in western France. Our study area was characterized by hedgerows surrounding arable ﬁelds and permanent grasslands. Some areas did not change much over a few decades, while ﬁeld enlargement and removal of hedges appeared in some places following agricultural intensiﬁcation,. The present paper aimed at examining if the landscape context around crop fields affected the abundance of aphids (either directly, or indirectly via their natural enemies) and if this effect depends on the landscape scale considered. We observed that the abundance of aphids in the field was associated with landscape composition at large scale (500 m and 800 m). There was a positive correlation between the abundance of the aphids and the proportion of woodland and grassland at these scales. There was a negative correlation between the abundance of carabids and the proportion of grassland and hedgerow around crop fields. The species richness of carabids was positively correlated with the proportion of hedgerows . We found that the proportion of grassy strips affect negatively the abundance of aphids in the wheat fields, and positively so in maize fields. Carabid abundance was positively correlated with the proportion of grassy strips at large scale in both types of cultures.
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