Factors Responsible for the Attractiveness of Various Clones of Alfalfa to Pollen‐Collecting Bumble Bees 1

N INITIAL objective of the -research work started in A 1946 at the Legume Seed Laboratory, Logan, Utah, was to discover a fundamental basis for differences in attractiveness of various clones of alfalfa to bees. That clone C-11 was especially attractive to several species of leaf -cutting bees (Megachile) had been observed previously by Vansell and Todd (16). It was hoped that a study of the attractiveness of various clones would assist breeders concerned with improving seed production as well as furnish valuable clues for a parallel investigation of factors responsible for environmental differences in attractiveness of alfalfa. Since collection of alfalfa pollen by bees appeared to be largely independent of nectar collection, it was believed that a different set of factors might be responsible for the two activities. Whether or not this is true remains to be seen. Since bees engaged in pollen collecting are more efficient “trippers” than nectar collectors, and since the intensity of pollen collecting has been observed to be more variable than nectar collecting, increased knowledge on the “pollen-attractiveness” of alfalfa should be of particular value. This report presents the progress made with a study of a group of clones and their progeny using pollen-collecting bumble bees as indicators of attractiveness. Bumble bees are more adaptable to this purpose than are honey bees but the latter should also be used when suitable methods are developed. In the meantime it is hoped that the same factors are responsible for attractiveness of alfalfa to pollencollecting bees of different genera. Sugar concentration and volume are well established as factors governing the attractiveness of nectar sources to honey bees. Similar studies with regard to pollen have not been reported. Von Frisch (3) showed that information concerning pollen sources is transmitted within the hive in the same manner as information concerning nectar. However, studies involving preferences for one pollen over another have not been published. Work in progress at this laboratory with dishes of pollen has shown that such preferences exist but the bases for selection have not been determined. In general, Todd and Bishop (13), Percival ( lo ) , and Synge (12) agree that intake of pollen by the colony is governed by availability in the field. Eckert (2) and other workers including the authors have noted large differences in the composition of the pollen intake of colonies standing side by side. The chemical composition of pollen has been described by several workers. However, work along this line is not extensive. Work on pollen enzymes was reported by Paton ( 5 ) . Pearson (6) determined the pantothenic acid content of pollen. Todd and Bretherick (14) determined the chemical composition of the pollen from 33 species of plants