Foraging behaviour ofApis ceranaon cauliflower and cabbage and its impact on seed production

Abstract

SUMMARYIn the Kathmandu valley of Nepal, cauliflower (Brassica oleracea var. botrytis) and cabbage (Brassica oleracea var. capitata) plants had averages of 7 branches with 600 flowers and 12 branches with 94 flowers, respectively. Flower diameter was 14.9 mm in cauliflower and 13.8 mm in cabbage. The yellow flowers of both crops opened in the morning and remained open for two to three days; the total flowering period of each crop lasted for about one month, with cauliflower beginning in mid-February and cabbage in mid-March. Apis cerana colonies were caged individually with plants of the target crops. Bees started foraging on cauliflower and cabbage at c. 07.00 h and 06.30 h, respectively, and ceased flight activity at c. 18.00 h and 18.30 h, respectively. Foraging on cauliflower started at ambient temperatures of 7°C. Peak foraging activity was between 11.00 h and 13.00 h for each crop. The duration of individual foraging trips was 26.9 min for cauliflower and 23.9 min for cabbage. Visits to individual flowers lasted from 4.3 to 6.7 s during the day in both crops; bees visited 5–8 flowers/min. On each crop bees collected either pollen or nectar but never both during the same foraging trip. For both crops, pollen collectors outnumbered nectar collectors during the morning while the opposite occurred in the afternoon. Individual loads of cauliflower pollen weighed 5–9 mg; cabbage pollen loads weighed 8–10 mg. Fruit set on cauliflower plants pollinated by A. cerana was 57% higher than on control plants (pollinators excluded) and 20% higher than on open- pollinated plants. Fruit set on cabbage plants following bee pollination was 27% higher than on open-pollinated plants; control plants did not set fruit. Siliques (fruits) from control, open-pollinated and bee-pollinated cauliflower plants had 3,15 and 20 seeds, respectively. Open-pollinated and bee-pollinated siliques of cabbage had 18 and 28 seeds, respectively. Germination of seeds from bee-pollinated plants was 16% and 12% higher than for seeds from control and open-pollinated cauliflower plants, respectively, and 28% higher than for seeds from open-pollinated cabbage plants.