Certain crops in Switzerland can benefit from more-species-and-individual-rich wild-bee communities. An Agroscope report shows how this could be achieved.
In 2014, the Federal Council passed the Swiss Federal Action Plan for Bee Health. This report summarises the work – commissioned inter alia by the Federal Office for Agriculture – of Agroscope and its research partners aimed at improving the data situation, acquiring new knowledge on this complex of issues and determining possible measures for promoting bees and pollination services.
Higher yield or better quality possible
On average, the level of pollination by insects in most of the crops studied (apples, cherries, oilseed rape, broad beans and raspberries) seems to be relatively good. Nevertheless, improved insect pollination would make in-some-cases significant production increases possible in a number of crops. This would include e.g. a 10% average increase in cherry yield, or an increase in the quality of the harvested crop (e.g. 10% larger Gala apples, fewer deformed raspberries), which is highly relevant for the producers.
In some crops, especially apple and oilseed rape, the honey bee was the most abundant pollinator species, and it was responsible on average for approx. 50% of flower visits. Bumblebees were by far the most important broad-bean pollinators, and were generally important pollinators for many crops, thanks to their usually high pollinating efficiency and their provision of pollination services even at low temperatures and during bad weather.
Cherries and apples benefit from wild-bee diversity
For apple and cherry crops, which are examined in greater detail, the studies show that optimal pollination in terms of yield and quality is achieved through the complementarity of honey bees and species-and-individual-rich wild-bee communities. In cherry production, the highest yields were achieved at locations with a high number of different wild-bee groups and greater wild-bee diversity, since this allows optimal cover of temperature niches by the pollinator communities.
Wild bees can be supported with the help of flower strips. The flower strips for pollinators introduced over the course of the Swiss Federal Action Plan for Bee Health (2014, 2016) are used as a food source primarily by polylectic (i.e. generalist) wild bees and honey bees, and can demonstrably support the reproductive success of such wild-bee species.
Early supplies of flower resources…
Early supplies of flower resources are important for the majority of wild-bee species, but these are difficult to achieve through annual flower strips sown in the spring. Instead, such flower strips are suitable for reducing the nectar dearth in the summer. Perennial flower strips and flower strips sown no later than the autumn of the previous year are in principle better suited to achieving an early supply of flower resources.
…and a diverse agricultural landscape are essential
Furthermore, a number of studies show the importance of diverse agricultural landscapes with a high proportion of different tree-and-shrub-rich semi-natural habitats such as species-rich forest margins and hedgerows together with herbaceous, blossom-rich habitats such as extensively managed meadows, wildflower strips or flower strips for pollinators.
Robust forecasts for pollinators, pollination services or the pollination-dependent yield-increase potential of crops using spatial models would be helpful. These, however, are not reliably possible with the available data and due to the complexity of influencing factors. Consequently, the spatial modelling approach is not recommended for predicting wild-bee numbers and their pollination services. For this, direct data collection in the field is essential.
- Optimal pollination can significantly improve yield or quality in individual crops, e.g. cherries, apples and raspberries,
- Existing annual flower strips for pollinators support the reproductive success of generalist wild-bee species; however, they have very few early-flowering species, which would be important for the majority of specialist wild-bee species.
- Early supplies of flower resources can be achieved by perennial flower strips or those sown in the autumn, supplemented with early-flowering plant species.
- A diverse agricultural landscape with herbaceous and blossom-rich habitats is essential for pollinator diversity.