Cap removal by honey bees leads to higher pollen rewards from grapevine flowers

Abstract

Pollen of wind-pollinated plants such as grapevine rapidly dries out and is blown away after the anthers dehisce. Therefore, from the point of view of a pollen-collecting bee, pollen from wind-pollinated flowers is best collected soon after it becomes exposed. In grapevine, pollen becomes available immediately after the calyptra is shed, a process also referred to as capfall.We show, for the first time, that honey bees foraging on grapevine actively remove the calyptra from flowers. Using manual cap removal, we estimate that cap removal increases the pollen yield by 70% compared to collecting pollen from flowers after capfall. The bees selectively foraged on inflorescences with high numbers of loose caps, thus further enhancing their pollen revenue. We discuss the possible benefits of cap removal by honey bees for the development of individual berries and grape bunches of certain varieties.