Results of the investigations into nectar secretion and pollen production of new cultivars of rape (Brassica napus L.)

The beekeeping value of several double-zero cultivars of winter rape cultivated in Poland was evaluated because apiarists found them less attractive for bees in comparison to older high erucic acid rape cultivars. Moreover, the investigations also involved several spring cultivars because they are being increasingly cultivated as a result of frequent frost on winter cultivars. New double-zero cultivars of winter rape produced nectar at a similar level to the standard high erucic acid cultivar Skrzeszowicki. The low erucic acid cultivar Lirajet was equal to Skrzeszowicki with regard to pollen production of flowers; the remaining cultivars produced less pollen Marita and Polo. However, all low erucic acid cultivars had more attractive flowers for bees compared to the cultivar Skrzeszowicki. All double-zero spring cultivars revealed similar parameters. Spring rape cultivars produced smaller amounts of nectar by 50% and higher amounts of pollen by 50% compared to those produced by winter rapes. The flowers of all cultivars produced more pollen than nectar sugar. Differences by year were found in nectar secretion and pollen production by individual flowers and in the rate of honey bee foraging (slightly smaller differences).