Pollinator sharing between mass-flowering oilseed rape and co-flowering wild plants: implications for wild plant pollination

Pollinating insects are not only important in wild plant pollination, but also in the production of a large number of crops. Oilseed rape production is increasing globally due to demands for biofuels which may have impacts on pollinating insects which visit the crop and on the pollination services delivered to co-flowering wild plants. In this study, we tested (1) the degree of pollinator sharing between oilseed rape and native wild plants in field margins and hedgerows and (2) the effects of oilseed rape on the quality of pollination service delivered to these wild plants. We found large overlap between flower visitors of wild plants and oilseed rape, but the composition of species overlap differed with respect to each wild plant species. Nearly all individual visitors caught on both the crop and foraging on wild species carried crop pollen, but more than half the insects also carried pollen from wild plants. However, very little oilseed rape pollen was deposited on wild plant stigmas. This shows that (1) oilseed rape overlaps in pollinator niche with most co-flowering wild plants, and (2) crop pollen deposition on wild plant stigmas is low which may indicate that it is unlikely to cause reductions in seed set of wild plants, although this was not measured here. Furthermore, wild plants in field margins and hedgerows are important sources of alternative forage for pollinating insects even when a crop is mass flowering, and we suggest maintenance and augmentation of field margins and hedgerows to provide alternative forage for pollinator conservation to continue provision of pollination services to both crops and wild plants.