A PRELIMINARY-ANALYSIS OF THE FLORAL PREFERENCES OF THE ALFALFA LEAFCUTTING BEE, MEGACHILE-ROTUNDATA

The comparative attractiveness to female Alfalfa Leafcutting Bees (Meg achile rotundata) of flowers of 209 species of vascular plants, repres enting 52 families and 154 genera, was examined by measuring visitatio n rates to bouquets under standardized conditions. The bees were attra cted to only 21 species, representing 14 genera and seven families. Tw o floral features appeared to be related to bee visitation: a flower l ength less than 13.5 mm; and a corolla tube up to 5 mm in length and u p to 3 mm wide. It is speculated that the critical maximum length of 1 3.5 mm for the flower, and 5 mm length by 3 mm width for the floral tu be, are respectively determined by the insect's length, combined head and extended mouthparts, and head width. No relationship was found bet ween attractiveness of the flowers and visible color of the corolla, r adial or bilateral symmetry, density of open flowers, and genus and fa mily of plants. Despite its name, the Alfalfa Leafcutting Bee was attr acted to Alfalfa (Medicago sativa) half as frequently as it was to Whi te Sweetclover (Melilotus alba) and Purple Loosestrife (Lythrum salica ria).