Honigbienen zur Bestäubung von verfrühten Süßkirschen im geschützten Anbau

The objective of the present work was to study ways of additional foraging of honey bees in a sustainable production of forced sweet cherries in a polytunnel in order to reduce any loss of bees and to substitute the annual re-introduction of new bumble bees (Bombus terrestris L.) which are lost after use. Three honey bee (Apis mellifera L.) hives were employed during the three weeks flowering in April 2006 in a closed, unheated polytunnel to pollinate sweet cherry cvs ‘Burlat’, ‘Earlise’, ‘Samba’, ‘Souvenir des Charmes’ and an unnamed clone on dwarfing GiSelA 5 rootstock at Klein Altendorf research station near Bonn, Germany. The central position of hive A allowed the honey bees to collect pollen and nectar exclusively from the flowering sweet cherries in the tunnel. Hive B also inside the tunnel had apertures inside and outside the tunnel, while hive C outside the tunnel adjacent to its wall, had inside and outside apertures; honey bees from the latter two hives were allowed to forage both inside the tunnel or outside. Differences in air temperatures between the inside and outside the tunnel were no more than 5?°C due to effective ventilation. A portable gas heater for automated frost protection maintained the night temperature in the polytunnel in April above 0?°C. Measurements of the flight activity showed a close correlation with the ambient temperature at the respective hive location. The two bee hives A and B within the tunnel showed larger flight activities of an averaged 540 bees per hour compared with 180 bees per hour outside due to low spring temperatures. Honey bee population A in the centre of the tunnel declined after three weeks pollination to ca. 9,200 individuals and produced only 46?kg honey due to shortage in food reserves and intense flight activity. The outdoor bee population C with ca. 15,000 individuals yielded also only 49?kg honey due to lack of flight activity during the cold April 2006 compared with 68?kg honey from population B with ca. 16,000 individuals but continuous flight activity within the tunnel and additional foraging outside. Control bee hives D and E with ca. 22,000 individuals each, which had remained at the institute at Bonn, produced 82–93?kg honey during the same time. Cherry forcing resulted in a 12–18 days earlier flowering in April 2006 relative to the 12–16 days earlier harvest in June 2006. Large fluctuations in yield of 0.3–15.4?kg/tree were due to commensurate S-alleles causing intersterility, insufficient fertilisation and location of the cherry cultivars relative to each other and the bee hive.