Hi all
One of the questions that has occupied me for the past few decades is why do queens sometimes get superseded and sometimes not. Also, do the workers initiate the process or is it the queen. As most of us know, Colin Butler died this January. In my opinion, he was closest to understanding this question than anyone. He wrote

The suggestion that queen supersedure is initiated by the worker bees
of a colony becoming aware that their queen is laying unfertilised eggs on
account of near exhaustion of her store of sperm (SNELGROVE, 1946) is
clearly invalid, as a number of cases have occurred at Rothamsted in
which both naturally mated and instrumentally inseminated queens have
become partial or complete drone-layers (i.e. come to lay unfertilised, drone 
producing eggs in worker cells). Despite this the bees of their colonies
made no attempts to rear new queens. In fact, as MACKENSEN (1951)
showed, it is possible by treating queens with carbon dioxide to cause
them to lay eggs without insemination, and such queens appear to be fully
capable of inhibiting the workers of their colonies from attempting to rear
further queens.

BUTLER (1954 b) showed that a substance which the worker bees obtain
by licking the body their queen is fully capable of inhibiting them from
rearing further queens. He further demonstrated that the larger the
number of worker bees the greater the amount of this queen substance
necessary to inhibit them from queen rearing. In Experiment I a queen
which had actually been superseded by her bees, but still remained alive,
was shown to be capable of inhibiting queen rearing in small colonies but
not in large ones. It seems fairly certain, therefore, that she had been
superseded because her production of queen substance was insufficient
to inhibit queen rearing in her own colony. It is, likely, therefore, that a
shortage of queen substance is the only immediate cause of queen supersedure,
and that disease and injury produce their effects, if any, by reducing
the ability of a queen to produce sufficient queen substance.

Butler, C. G. (1957). The process of queen supersedure in colonies of honeybees (Apis mellifera Linn.). Insectes sociaux, 4(3), 211-223.

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