Diversity and foraging behaviour of pollinators on onion Allium cepa L and their impact on onion seed production

Abstract

Studies on Diversity and foraging behaviour of pollinators on onion (Allium cepa L.) newlineand their impact on onion seed production were conducted during 2016-18 at ICAR-Indian newlineInstitute of Horticultural Research (IIHR), Bengaluru. Major onion seed production areas in newlineKarnataka were surveyed to document pollinator diversity on onion. In total, nine species of newlinepollinators were recorded from farmers fields, of which the majority belonged to the honey bee newlinegroup. However, at IIHR, Bengaluru, where observations were recorded from an unsprayed newlineexperimental plot of onion, diversity of pollinators significantly high with forty-five species newlinehaving been recorded. Among them, three species viz., Apis cerana, A. florea and Tetragonula newlineiridipennis were found to be the dominant ones based on the frequency of visitation. Diurnal newlinevariations indicate that the foraging activity of all species except T. iridipennis was at its peak newlineduring morning hours (9.00-11.00AM). Nectar analysis of onion flowers revealed the presence newlineof twelve sugars with fructose, glucose and sucrose as the dominant ones. Floral nectar newlineparameters were found to play an important role in attracting pollinators. Among three varieties newlinestudied, Arka Pragathi attracted the highest number of pollinators (8.42 honey bee/umbel/5min) newlinewhich had higher nectar volume (1.81 and#956;l/floret), total soluble solids (63.80) and energy (19.33 newlinejoules). The exclusion of pollinators from onion flowers resulted in about 85 % reduction in the newlineseed set. Pollination by Indian honey bee, A. cerana resulted in the highest seed yield and newlinequality. Evaluation of natural compounds confirmed the efficacy of spraying jaggery solution newline(10 %) in attracting the highest number of pollinators. Honey solution (10 %) and sugar solution newline(10 %) were the next best treatments to augment the pollinator population in the field. newline