Abundance and diurnal rhythm of honeybees visiting hybrid seed production plots of cauliflower (Brassica oleracea var. botrytis L.)

Abundance and diurnal rhythm of honeybees on parental lines were studied in hybrid seed production plots of cauliflower (Brassica oleracea var. botrytis L.) for two years (2001-2003 and 2002-2003) at the Indian Agricultural Research Institute, Regional Station, Karnal, India. In both years, Apis species were the predominant pollinators with Apis dorsata the most abundant. Pollen gatherers outnumbered nectar collectors. Bee foraging populations were significantly different among sowing dates in both years. Honeybee foraging activity was found to be highest between 12:00 to 14:00 hours, and bees preferred to visit parental lines. Apis florea spent more time per flower and plant than other species. Apis dorsata visited more flowers per minute followed by Apis florea. Honeybees spent more time per flower and plant and carried more pollen on their bodies in the morning than afternoon. Among bees, Apis dorsata carried more pollen on its body. Flower nectar volume (mu l) was higher in mornings and nectar sugar content higher in the afternoons. There was no significant variation in parental lines with regard to nectar volume. Nectar sugar content differed significantly between parental lines in 2001-2002; the female line had more nectar sugar content than the male line. Bee activity was positively correlated with temperature, light and nectar sugar in both years. But RH, wind velocity and nectar volume negatively correlated with bee activity.