Pollen sources

Honey bees and wild bees need pollen for the supply of protein and fat, which they collect in the flight range from the plants growing there. However, pollen is of varying quality and value with regard to its protein, lipid and vitamin content and the proportion of essential amino acids as well as its digestibility.

For Austria there are no comprehensive studies available to date on the seasonal and regional pollen sources used by bees and their diversity. The aim of the project module was to close this gap in order to obtain basic information on these questions, which are important for public development and bee health. Beekeepers were involved as voluntary samplers, so-called "Citizen Scientists".

The pollen analysis was initially carried out roughly by assigning colours to harvested pollen pellets at fixed dates throughout the year, and on a second level by light microscopic assessment and botanical identification of pollen-producing plants, which, however, could not always be carried out up to species level.

At the first collection willow pollen clearly dominated. At the second date pollen from willows and apple, pear and hawthorn, but also rapeseed and horse chestnut were strongly represented. Maple dominated at the third date, followed by rapeseed, other cruciferous plants and various ranunculaceous plants. From the fourth collection date onwards, white clover, plantain, mustard and red clover were increasingly used as pollen sources. The plantain species and the white clover remained dominant until the 7th and 8th collection dates respectively. From the 7th date onwards, various lateblooming Compositae, mustard, phacelia and buckwheat were also collected strongly from the bees. At the end of the season on the 9th date, ivy pollen was dominant in both years.

Of special interest were the greening with Phacelia tanacetifolia, Sinapis spp., Fagopyrum spp. and other members of the cruciferous plants, which bloomed in late summer and well into autumn and which were viewed critically by parts of the beekeeping community with regard to an extension of breeding activity and the resulting problems with bee health (extension of the breeding period of the varroa mite, dysentery, Nosema) and the success of overwintering. Here it was shown that there are apiaries where the pollen of the mentioned plants plays a role in the late summer pollen supply, as well as apiaries where this is not the case.

Of particular interest in the assessment of a site with regard to pollen diversity is the comparison between country and city. This question helps us to understand which land use types best supply honeybees and other pollinators with pollen in today's highly man-made environment. Due to the relatively few apiaries investigated in cities, our study provides only exemplary results that support the assumption that urban sites are good pollen habitats.

In any case, the quality of the individual pollen must also be taken into account, since the pollen of individual plants, such as horse-chestnuts, have a significantly higher nutritional value for honeybees than many other pollen species. Therefore, pollen of plant species that is collected at a certain time as the dominant pollen and often collected in almost pure form, should be investigated towards its nutritional value for honeybees. This could then give beekeepers the opportunity to take countermeasures if necessary and to ensure a correspondingly balanced food supply.