Does the honeybee (Hymenoptera: Apidae) reduce the blooming period of canola?

Abstract

The aim of this study was to determine if and how the honeybee reduces the blooming period of canola (Brassica napus). Colonies were installed in different fields of canola in the Chaudiere-Appalaches (two replicates) and Quebec City (one replicate) regions to create a density gradient of zero to three colonies per hectare. To calculate the blooming period under these conditions, 10 labelled plants were caged in the field, out of the reach of pollinators, and 10 others were labelled in the field and exposed to foragers. The number of flowers found on each plant was recorded daily. This study also aims at demonstrating that the canola plant will produce new flowers as long as it does not reach its maximum carrying capacity, thereby extending the blooming period. To simulate the fall of unfertilized flowers, a predetermined number of flowers from 20 randomly selected plants in one of the replicates were cut off every day. The plant, when it reaches its maximum carrying capacity, stops producing new flowers. With three colonies per hectare, the blooming period was reduced by 3.8 days, or 17% compared with in the absence of pollinators. Because of the efficient pollen transfer to the stigma, the honeybees do not only cause the flower to live for a shorter period of time, but they also bring about a decrease in the number of flowers produced by the plant, thereby reducing the duration of blooming period. © 2006 Blackwell Verlag.