Pollen source preferences and pollination efficacy of honey bee, Apis mellifera (Apidae: Hymenoptera) on Brassica napus crop

Brassica napus is an insect-pollinated crop species and offers itself as the main nutrient source to many insects that consume floral nectar. This study was carried out to ascertain the pollen preferences of Apis mellifera among the available floral resources. We wanted to identify and quantify all types of pollen collected by honeybee during the flowering period. Moreover, the foraging rate and pollination efficacy of managed honey bee colonies (placed at 250 and 500 m distance away) on B. napus crop were determined. The results revealed that A. mellifera foraged efficiently on 18 plants species belonging to 11 families during the flowering period of the Brassica crop. The Asteraceae family was represented by six plants species as pollen sources followed by Solanaceae, Malvaceae, Fabaceae, and Rosaceae represented by two plant species from each family. One floral source included Brassicaceae, Convolvulaceae, and Poaceae families. Among 18 identified plant species, 6 were weeds, 4 herbs, 4 shrubs, and 2 species each were from crops and ornamental plants. In this study, weeds were reported as the major bee supporting bee flora followed by shrub and crops. The identified pollen grains had different morphology such as sub-spheroid, prolate shape, spheroid, ovate, glandular, triangular, round, and oval shape. The maximum foraging activities of bees on B. napus took place during day hours particularly at 12:00 PM followed by 14:00 PM, and then at 10:00 AM weekly. The study revealed that the total number of pods per plant, total number of seeds per 100 pods, and weight of seeds per 10 plants were significantly higher in bee-pollinated flowering plants compared to flowering plants with no bee-pollination.