The potential of weeds and field margins in providing ecosystem services and hosting syrphids

Conventional agriculture and its intensive use of chemical inputs has had a negative effect on agricultural flora and fauna. By taking an ecological approach to agricultural, it is possible to take advantage of natural resources and manage cultivated fields in a sustainable manner by promoting the presence of wild vegetation that may in turn provide ecosystem services. This vegetation can be found both in fields, as weeds, and in field margins. Field margins are known to provide resources to beneficial insects such as syrphids (Diptera: Syrphidae). In this thesis, we explore the potential of uncultivated vegetation in providing ecosystem services and hosting syrphids. In Chapter 2, results from a systematic review of ecosystem services provided by weeds are presented. In total, 129 articles were found that contained examples of weeds providing ecosystem services. Most examples were of weeds promoting natural enemies of pests. However, very few studies were designed to test ecosystem services provided by weeds and hardly any studies were able to disentangle the beneficial effect of weeds from the yield reduction through competition for resources. In Chapter 3, herbaceous vegetation community composition in the field margin is shown to be influenced by the field margin component type (e.g. shrub, grass strip, or ditch), the adjacent land use, and soil properties. Woody field margin components were found to contain more species that provide nectar and pollen for insects than other field margin component types. In Chapter 4, we show that the abundance of syrphids in field margins is affected by field margin components, floral resources, and adjacent land use. We highlight the importance of maintaining a diversity of field margin structures in the agroecosystem to promote syrphids throughout the calendar year. In Chapter 5, we demonstrate that syrphid assemblages are influenced by field margin complexity (in terms of number of components), flower resources, adjacent land use, and vegetation composition. In conclusion, by managing weeds and field margins, it is possible to promote ecosystem service provisioning in agroecosystems. The inclusion of different types of components in the field margins can contribute in providing flower resources to syrphids and maintaining a diverse community.