The effects of wheat-pea mixed intercropping on biocontrol potential of generalist predators in a long-term experimental trial

Arthropod generalist predators can be effective natural control agents of pests and weeds in agroecosystems. Their activity and contribution to biocontrol may increase in response to more complex agricultural habitats. In this study, we investigated the effects of winter wheat-pea mixed intercropping on the biocontrol potential of generalist predators compared with the respective mono-crops. We evaluated not only the effects during the intercropping season but also the pre-crop values of the mixture for the subsequent barley crop. Furthermore, we evaluated the influence of different long-term soil organic carbon and fertility management regimes on activity and biocontrol potential of predators. Field work was conducted over two seasons in a field experiment located in Gembloux, Belgium. A set of proxies for ecosystem functions were measured using the Rapid Ecosystem Function Assessment approach. We measured attack and predation rates of sentinel prey and weed seeds artificially placed in the field. Furthermore, we assessed activity density of the main groups of generalist predators during the exposure of the baits. Our results showed that crop type affected activity and biocontrol potential of predators. Predation rates were much lower in wheat than pea and wheat-pea. The mixture wheat-pea had a positive effect on predator activity density compared to wheat mono-crop, while pea supported an intermediate activity of epigeal predators. In the second season of the field work, we found the highest biocontrol potential by predators in barley plots cultivated after pea. Finally, our results failed to find any differences in biocontrol potential of predators between long-term soil organic carbon and fertilisation management strategies. These results suggest that crop type has a major relevance in influencing the activity of generalist predators, and the mixed intercropping wheat-pea may represent a valid strategy to enhance biological pest control in comparison to wheat cultivated as mono-crop. Furthermore, we show that the cultivation of pea as mono-crop may have an important pre-crop value within the rotation increasing the provision of ecosystem services such as biocontrol.