Morphometric Studies on Bumble Bees

Measurements were made on the radial cell of the forewing, glossa, prementum, and first segment of the labial palpus of 35 species of bumble bees. Correlation coefficients were positive and highly significant between all possible combinations of the measurements, except in a very few cases involving the glossa. Because the measurement of the radial cell can be correlated positively with the tongue length, and the radial-cell measurement can be used to determine size variations, it should be possible to utilize the radial-cell measurements in future studies that are concerned with the relationships between tongue lengths and the nectar-gathering behavior of the species of bumble bees reported on in this research. A labial index, determined by dividing the length of the prementum by that of the first segment of the labial palpus and multiplying by 100, was found to be characteristic for each species, and provided an interesting method of studying relationships between the species in the various subgroups. When the labial index data were applied to conventional groupings of the bumble bees, most species appeared to be closely related with regard to the mouthpart character. However, with regard to the pratorum group, the placing together of certain species from North America and Europe does not appear to be a natural one. Tables are presented with the means and standard deviations of the four measurements of the queen, worker, and male castes of each species.