Aphid suppression by natural enemies in hedgerows surrounding greenhouses in southern Spain

Abstract

Southern Spain is home to the most intensively grown protected crop area in the EU. The area is currently characterized by greenhouse monocultures and a homogenous landscape. The establishment of hedgerows among greenhouses can enhance the diversity of natural enemies of pests around the greenhouses and help them thrive. However, the effect of hedgerows on pest control has not been addressed. Thus, we used aphid banker plants, i.e. wheat infested with Rhopalosiphum padi (L.), as sentinel plants in the surroundings of three paired greenhouses with and without hedgerows. We assessed the effect of hedgerows on the abundance of aphids and arthropod community populations. In addition, we assessed the importance of the surrounding environment on aphid survival. There were 4.1-fold more aphids on sentinel plants excluded from the action of natural enemies than ones exposed to them, showing that biological control occurs naturally even in a simplified greenhouse agrosystem. Aphid populations were slightly higher (albeit not significantly) in replicates without hedgerows than in those with hedgerows. The percentage of greenhouses, rather than hedgerows, was an essential factor in suppressing aphids, highlighting the importance of using commercial biological control in greenhouses. The presence of hedgerows resulted in changes in arthropod composition populations, i.e. in a lower occurrence of pests and a higher occurrence of natural enemies, especially in the most simplified replicate. We propose increasing the amount of hedgerows for reducing pressure from pests on simplified greenhouse agrosystems.