Relationship between the abundance of aphids and their natural enemies in cereal fields and landscape composition

We investigated, over the course of two years, the association between the abundance of aphids and their natural carabid enemies and landscape, which may help in the development of effective strategies for reducing the incidence of aphid outbreaks in agricultural crops. This was undertaken in 12 wheat and 12 maize fields each year in an agricultural landscape in western France. Our study area was characterized by hedgerows surrounding arable fields and permanent grassland. Some areas have not changed much for several decades, while field enlargement and removal of hedges occurred in some areas following agricultural intensification. This paper aims to determine if the abundance of aphids in crops (either directly, or indirectly via their natural enemies) is associated with the landscape around fields and if so, is it dependent on the landscape scale considered. We observed that the abundance of aphids in fields was associated with landscape composition at a large scale (500 m and 800 m). There was a positive correlation between the abundance of aphids and the proportion of the area under 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 abundance of aphids in wheat fields was negatively and in maize fields positively associated with the proportion under grass strips. At a large scale carabid abundance in both types of culture was positively correlated with the proportion under grass strips