Pollination efficiency and foraging behaviour of honey bees and flies to onion Allium cepa L.

Abstract

Bees and flies are the most common visitors to onion flowers in Karnataka, but evidence for their pollination efficiency is lacking. Hence, experiments on pollination efficiency and behavioral observations were recorded using four bees (Apidae: Hymenoptera) and two flies (Syrphidae: Diptera) species visiting onion flowers (Allium cepa L.) at the experimental fields of ICAR-Indian Institute of Horticultural Research, Bengaluru, Karnataka, India (13.13°N; 77.49°E) during 2020-2021. Pollinator effectiveness (PE) is measured as pollen deposition on stigmas per visit. Honey bees and flies mainly collect nectar and stingless bees mainly pollen (81.90%), bringing the latter into intimate contact with the stigma more frequently. Stingless bees, honey bees and flies were often seen foraging together on the same umbel, and no antagonistic interactions were observed. The rock bee (Apis dorsata) deposited a maximum number (34.60) of pollen on stigma per visit followed by the stingless bee (24.45). The flowers pollinated by bees had a higher seed set percentage; the weight of 1000 seeds and the average number of seeds/umbels were higher compared to flowers deprived of pollinators. The results allowed us to conclude that bees are the effective pollinators of onions. Further work is needed to determine the optimum bee population required for maximizing the seed yield in onion.