DENSITY, DIVERSITY, AND EFFICIENCY OF POLLINATORS OF SAINFOIN, ONOBRYCHIS VICIAEFOLIA SCOP.

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Abstract
The density and efficiency of bumble bees, honey bees, and alfalfa leafcutter bees on sainfoin, Onobrychis viciaefolia Scop., grown in southern Alberta were studied. Six species of bees were identified as pollinators, with alfalfa leafcutter bees comprising 56% of the observations, honey bees 40%, and bumble bees 4%. The density of flowers over the season can be described as curvilinear. The mean number of flowers per raceme decreased significantly over the season. The rate of foraging by pollinator species from flower to flower varied and is described by multiple regression models. Julian date, hour of day, and flower density are the independent variables. More than 90% of the bees visited three or fewer flowers per raceme when 60% of the racemes had three or more flowers available for pollination. The bees foraged on sainfoin for about 12 h per day and average bee density increased significantly with the corresponding flower density. A theoretical approach used to predict the bee populations required to pollinate varying flower densities shows that the required population of bumble bees is about two-thirds that of honey bees or alfalfa leafcutter bees. The observed populations of pollinators did not correspond well with the derived values, probably because multiple visits per flower are required for fertilization.