From petals to seeds: Understanding the role of hymenopteran and dipteran pollinators in the reproductive success of onion (Allium cepa L.)

Abstract

An experiment was conducted to assess the pollinator community of onion (Allium cepa L.) as well to find the pollinators contributing to a higher onion seed production. Fifteen insect pollinator species belonging to two orders and two families were found to be visiting onion flowers. The dwarf honeybee, Apis florea F. (Hymenoptera: Apidae) was most frequent pollinator among bees. The maximum visitation rate was recorded in the case of Eristalinus aeneus S. (Diptera: Syrphidae), while the maximum stay time was recorded for A. florea. For observing the pollination effectiveness, we used pollinator exclusive approach, and four pollination trials were maintained i.e., 100%, 50%, 25% and 0% pollination. Pollinator effectiveness was accessed in terms of yield parameters such as umbel weight, number of seed and seed weight. Compared to 0% pollination, plants with 100% and 50% pollination levels showed 44- and 19-times higher seed production in onion, respectively. Six major pollinators were tested for their pollination efficiency. The single visit efficiency in terms of the number of seeds showed that plants with A. florea pollination showed higher seed yield. There was an increase in the number of seeds and seed weight per umbel, proving that A. florea is an effective pollinator in onion production. Moreover, syrphid flies also contributed to the onion seed production, though they were less efficient pollinators.