Strip intercropping of wheat and oilseed rape enhances biodiversity and biological pest control in a conventionally managed farm scenario.
Abstract
Conventional agriculture in the global north is typically characterized by large monocultures, commonly managed with high levels of pesticide or fertilizer input and mechanization. Strip intercropping, that is, diversifying cropland by growing strips of different crops using conventional machinery, may be a viable strategy to promote natural predator diversity and associated biological pest control in such conventional farming systems. We tested the influence of strip intercropping of conventionally managed winter wheat with oilseed rape, using common machinery with 27-36 m broad strips, on arthropod predator diversity and biological pest control. We characterized spider and carabid beetle communities, calculated pest aphid and pollen beetle densities and recorded parasitism rates for both crops (number of mummified aphids on wheat and number of parasitized pollen beetle larvae on oilseed rape). We observed a significant reduction in the densities of wheat aphids (50% decrease) and pollen beetle larvae (20% decrease) in strip intercropping areas compared to monocultures. Parasitism rates of wheat aphids increased significantly from 10% in monocultures to 25% in strip intercropping areas. The number of parasitized pollen beetle larvae did not show the same pattern but was higher towards the centre of the oilseed rape strip. Overall, the composition of predator communities benefited from the close neighbourhood of the two crop species in the strips, as carabid beetles were more abundant in oilseed rape and spiders were more abundant in wheat fields. Overall, strip intercropping reduced the dominance of one predator group and allowed for an equal representation of both spiders and carabid beetles in the mixture. Synthesis and applications. Our study presents evidence of the benefits of adopting strip intercropping with relatively large strips (adapted to existing machinery) for natural predator diversity and biological pest control in a large-scale conventionally managed farm scenario. Wheat-oilseed rape strip intercropping reduced pest densities, increased parasitism of wheat aphids and promoted equal representation of natural predator groups well beyond the areas of monoculture. Overall, by reducing the area dedicated to only one crop, the implementation of strip intercropping adapted to mechanized agricultural scenarios can be used to increase crop heterogeneity at regional scales and enhance biodiversity and biological control, even in simplified landscapes dominated by large-scale conventional agriculture.