I really don't know about a biological clock related to season and
the lengthening of daylight hours, but I do know that the literature
is full of discussion of the success of bees brood rearing on various
pollens and supplements.
 
Henry Pirker wrote an article years back "Steering Factor Humidity"
that decribed the correlation of brood rearing and humidity in bee
houses in Northern Alberta.  He tinkered with humidity and
temperature and could control brood rearing at will. (I am only
familiar with the mechanisms that we see here in country where we
have 10 months of winter and two months of poor skiing.  It is
currently minus 17 Celcius here -- and this is quite a heat wave
compared to the last three weeks).
 
Interior temperature and humidity of the winter cluster is a factor,
and this is related to whether the bees are calm or stimulated, as
well as the environment.  In the fall, temperatures decline
progressively over time, as do daylight hours and sun angle. One
irritant that may cause some restlessness and warming in the hive
over time is the buildup of feces in the bees.  Aging of the
population may also be a factor causing more activity, since older
bees normally want to go outside.
 
If bees are properly prepared for winter, in late fall, older bees
have generally left, and the bees are sitting on a lot of honey which
buries the pollen they need for brood rearing.  They will even bring
up honey from below and fill the upper box.  Consequently, they have
little pollen available, but as winter progresses, they uncover this
pollen and are able to rear brood.
 
We notice in the summer that pollen income is a large factor in the
amount, quality, and duration of brood rearing, and the decline in
brood rearing in the fall is related to the decline in successful
foraging for pollen and reduction in bee activity. Cool days after an
early frost result in cutting back compared to years where frost is
late and days are warmer.
 
Hive populations are a factor, and once peaked in summer, mature
hives reduce brood production compared to splits in the same yard.
In late winter, poulations are reduced due to attrition, so small
populations may be a factor.  Additionally, other factors being
equal, empty (light) hives are more active than full (heavy)
ones.
 
In Alberta we seldom see more than 3 or 4 frames of brood before the
spring pollen begins in earnest, and this is sometimes pretty spotty.
 Thin syrup or a honey flow are very important too, since they supply
ready food and moisture.  There seems to be a concensus that sucrose
is stimulative compared to honey as a feed, and nectar contains
mostly sucrose.
 
To sum, I believe that the major factors are in roughly declining
order of importance: Pollen, humidity, population, nectar income.
 
As far as a biological clock?  I don't know.
 
 
 
 
 
Regards
 
Allen
 
W. Allen Dick, Beekeeper                                         VE6CFK
RR#1, Swalwell, Alberta  Canada T0M 1Y0
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Honey. Bees, & Art <http://www.internode.net/~allend/>