Phylogeny of Bumble Bees Based on Brood-Rearing Behaviour

Abstract

Studies of 19 species of bumble bees, Bombus Latr., representing seven of the nine subgenera that occur in North America north of Mexico show that queens construct first broods in at least two ways. Queens of species belonging to the subgenera Subterraneobombus Vogt, Fervidobombus Skor., Pyrobombus D. T., Bombus., Latr., Cullumanobombus Vogt, and Bombias Robt. construct adjoining cells of pollen and lay a single egg in each. When an egg is laid, the pollen forming the wall of the cell is immediately manipulated with the mandibles to enclose the egg. Usually, an egg is laid when a cell is completed, but sometimes as many as four cells are made before any eggs are deposited. Two to three days are needed to complete the first brood mass, which usually consists of about 10 eggs. Additional pollen, on which the first-brood larvae apparently feed, is packed beneath the brood mass after all the eggs are laid and after the envelope covering the eggs in the cells has been infused with wax. The pollen is packed beneath the cells through gaps in either end of the wax-pollen envelope covering the brood. Honey is fed to the larvae by biting holes in the envelope and pumping the honey into the cells. The holes are repaired immediately after the larvae have been fed. Queens of balteatus Dahl. of the subgenus Alpinobombus Skor. deposit the full complement of first-brood eggs in a single cell built out of a rough mass of pollen. The eggs are deposited in vertical positions as are the first-brood eggs of species that lay only one egg per cell. Pollen is added to the base in the manner described above.