When the bumble bee, Bombus terrestris, was reared under controlled conditi
ons in the laboratory for many generations, queens with a wet weight of 1 g
or more were no longer produced after several generations. At present it i
s unknown what causes the disappearance of these heavier queens. In this pa
per three possible explanations are given: (1) inbreeding, (2) altered ener
gy allocation strategy such that more but lighter queens are produced, (3)
a gradual build-up of a deficiency of scarce nutrients. No proof was found
for a negative effect of inbreeding on the weight of queens, and colonies d
id not produce more queens. This suggests that the disappearance of heavy q
ueens is caused by a deficiency of scarce nutrients.