Reduction in the availability and quality of plant food resources through arable intensification and habitat fragmentation has been cited as a major cause of the decline in pollinators in the UK and worldwide, and is likely to have a negative impact on the activity and abundance of natural enemy species that rely on floral resources in their adult life stages. Many pollinator and natural enemy groups disperse over large distances in search of pollen and nectar, and this might be exacerbated in intensively-managed systems with low resource diversity. Alternative management systems that lead to increases in resource availability and quality for these insects are therefore likely to promote both diversity, through niche differentiation, and fitness, by reducing the need for insect foraging over large distances. Thus, management to increase within-field and farm-scale vegetation diversity is one option to combat declines in pollinator populations and promote numbers and activity of natural enemies.
At the Balruddery long-term sustainability research platform, we are comparing the impact of conventional versus ‘sustainable’ management approaches on arable ecosystem function and productivity. This farm-based research platform is the first of its scale in the UK, and provides a unique opportunity for empirically testing assumptions about the effects of agriculture on the services provided by pollinators and natural enemies. If competition for limited resources is one of the factors underlying fluctuations in native insect populations, then a sustainable approach to managing arable systems that leads to improved resource availability and diversity should have a positive impact on insect abundance and/or diversity. Under the sustainable cropping system, herbicide applications are reduced to encourage a moderate understorey of dicot weeds within the cropped area. In the field margins, diversity and resource type are manipulated by direct sowings of native wildflower mixes, buckwheat and other species thought to provide high quality floral resources. These are compared directly with standard in-field weed management and grassy margins under the conventional cropping system.
Pollinator surveys are carried out in the field margins and in flowering crops (beans and oilseed rape) to assess differences in the abundance of hymenopteran and dipteran pollinator species between cropping systems. Pollination rates are measured in faba bean crops through comparison of bean set in hand pollinated, bagged and open bean plants to relate pollinator numbers to pollination services.
Natural enemy abundance is measured as abundance of the main predatory and parasitic invertebrate groups from pitfall trapping and vortis suction sampling in field margins and cropped areas under both cropping systems and all six crop types. Parasitism rates and the abundance of specific parasitoids and their aphid prey are measured directly in beans, barley and potato. Further details and preliminary results of these surveys can be found on the Centre for Sustainable Cropping long-term platform website.
This work links with SG funded work on IPM, novel crops and integrated management systems, and EU funded work on arable diversification.
Contact Cathy Hawes for further information
