Unterschiede in der Kastendetermination zwischen den Hummelarten Bombus hypnorum und Bombus terrestris / Differences in the Caste Determination between the Bumblebee Species Bombus hypnorum and Bombus terrestris

In colonies of Bombus hypnorum reared in captivity all intermediate body sizes between worker and queen are produced, the body size being determined by the amount of food for the larvae. Queens are produced, if the larvae are fed sufficiently. In captivity queens are produced at every time of the colony development, if one worker has to feed only two larvae in the maximum. In experiments where queens founded a colony together with workers, the larvae of the first brood also developed into queens. In Bombus terrestris the castes are more differentiated. Workers have a maximal body size and there are no intermediate sizes to the queen size. Larvae are determined alternatively to be workers or queens in the first 3½ days of the development. Experiments with fences show that the queen produces a pheromon which inhibits the workers from rearing new queens. Workers are not able to pass the inhibiting factor from one to another. The inhibition by the queen terminates near the end of the colony development.