Neighbourhood effect of faba bean (Vicia faba L.) on density of vegetation-dwelling natural biocontrol agents in winter wheat

Legume crops such as faba bean (Vicia faba L.) have been underrepresented in conventional cropping systems in Europe for decades for economic reasons, even though faba bean is a native crop and suitable to diversify local cropping systems. While the environmental benefits that go along with faba bean cropping are well established, there is a gap of knowledge on the effects faba bean may have on biodiversity and associated ecosystem services, such as natural biocontrol in agricultural landscapes. The aim of the present field study was to quantify neighbourhood effects of faba bean on densities of vegetation- dwelling natural biocontrol agents and herbivores in adjacent winter wheat. Densities of predators, herbivores, parasitized aphids (mummies) and leaf damage by the cereal leaf beetle (CLB) were assessed by repeated visual counts in conventionally managed winter wheat crops. In winter wheat adjacent to faba bean, total predator density was higher than in wheat adjacent to winter wheat, independent of the observation period. This effect was not reflected in the predator-prey ratio though. The total density of mummies and parasitism rate were not affected by the neighbouring faba bean crop. Predator density decreased towards the field centre. CLB leaf damage and yield were not affected by the neighbouring crop. All densities were affected by the observation period. The effects were measurable in spite of the external management such as insecticide application, which had a negative effect on both predator and herbivore densities. The present study sheds first light on faba bean effects on natural biocontrol agents in conventionally managed agro-ecosystems. While few, effects were measurable, which shows the need for further research on the association of faba bean cropping with the ecosystem service natural biocontrol.