Influence of the apetalous character in rape (Brassica napus) on the foraging behaviour of honeybees (Apis mellifera)

In order to establish whether commercial hybrid seed production between apetalous and apetalous rapeseed lines could be developed through insect cross-pollination, observations were made to compare the foraging behaviour of honeybees on both flower types with regard to their attractiveness. Number of flowers/m2 and nectar volumes, considered as important attractive factors, did not differ between the two lines but nectar sugar composition was slightly different. Honeybee density was significantly higher on the apetalous line when their foraging activity was rather high. Honeybees showed a considerable constancy to each flower type. Passages between both types were not very frequent. Nectar foraging behaviour, observed under cages, differed with the floral morphology. On the apetalous flowers, honeybees visited the two inner nectaries by crawling over the anthers and the stigma, while on the apetalous ones they often inserted their tongues between the sepals, thus having less contact with the reproductive organs. From these results, the honeybee efficiency in cross-pollination between petalous and apetalous lines appears to be reduced.