Are queen Bombus terrestris giant workers or are workers dwarf queens? Solving the 'chicken and egg' problem in a...

In the social bee, Bombus terrestris, the two castes differ in size and physiology, but not in any other morphological and anatomical aspects. The size differences between the castes are the result of longer instar duration in prospective queen larvae. It appears that queen larvae are programmed to have a higher molting weight at the end of the 2nd, 3rd and 4th instars. Calculation of the growth ratio, the ratio between the logarithm of molting weight at two successive instars, revealed that queen larvae have a linear growth ratio over the entire larval development as predicted by Dyar's rule. In the worker larvae, in contrast, linearity of the growth ratio breaks after the second instar, resulting in larval molting at lower weights than expected by Dyar's rule. We therefore suggest that workers' development is abnormally shortened, either by parental manipulation or by adopting a different growth plan in response to the queen's signal.