Non crop habitats have been found to increase the abundance of different predator groups feeding on crop herbivores. Plant species of semi-natural habitats such as field margins are refuges and provide resources for important predator groups. The floristic composition of such habitats has been suggested as a key factor since plant species differ in resource provisioning and other habitat functions. However, empirical evidence for the role of plant species composition in the control of crop herbivores is still lacking.

In this study, we will analyse the relationship between floristic composition of field margins and the control of major herbivores in oilseed rape and wheat fields. The study aims to identify plant species or functional groups that may improve this ecosystem service. We studied 32 wheat and 32 oilseed rape fields in Western France during two consecutive years. Data collection included entomological surveys in the field (insect abundance, crop damage, herbivore parasitism) and the analysis of adjacent field margin vegetation (plant cover and phenology).

Several vegetation parameters (diversity and cover of functional groups) were positively correlated with predation of crop herbivores and negatively correlated with herbivore abundance and damage. However, we also found undesired interactions between field margin flora and crop herbivory. The results may help to improve the contribution of the field margin flora to biological control by designing and planting suppressive seed mixtures or by favouring desired plant species (field margin management).