Biological pest control and yields depend on spatial and temporal crop cover dynamics

Abstract

Summary Modern agricultural landscapes are dynamic systems with interannually changing proportions of different crop types. However, the effects of spatiotemporal changes in crop area on crop yields and crop–herbivore–antagonist interactions have been rarely considered, in contrast to documented beneficial effects of semi‐natural habitats on biological pest control at local and landscape scales. In this study, we examined how the proportion of oilseed rape (OSR) fields in a landscape and the annual increase or decrease in OSR cover due to crop rotation affect OSR herbivores, their natural enemies and crop yield. During two study years, we examined the abundance of adult and larval pollen beetles, parasitism of pollen beetle larvae by a parasitic ichneumonid and crop yields (seed weight per plant) in the edge and centre of 36 OSR fields. The fields differed in the proportion of OSR in the surrounding landscape at 1‐km radius and in the interannual change in the proportion of OSR from the previous year to the respective study year. Adult pollen beetle abundance decreased in one study year and larval pollen beetle abundance and parasitism rates decreased in both study years with spatially increasing OSR proportion in the landscape, indicating dilution effects on both trophic levels. Crop yield was positively affected by spatially increasing proportions of OSR. An interannual increase in the proportion of OSR led to the dilution of pest species, but had no significant effect on yield or parasitism rate. Synthesis and applications. The negative effects of pollen beetles on yields despite regular insecticide applications underpin the need for improved techniques for controlling this pest. Our results emphasize the potential to enhance crop yields by the management of spatiotemporal crop cover dynamics within landscapes. We recommend that future management schemes should coordinate the spatial aggregation and annual dynamics of oilseed rape (OSR) cover in a landscape as a potential way to reduce pest impacts in intensively managed OSR fields.