Rueppell, O., Kaftanouglu, O., & Page
Jr., R.E. 2009. Honey bee (Apis mellifera) workers
live longer in small than in large colonies.
National Institutes of Health 44(6-7):
447–452.
In their 2009 study of European honey bees (Apis mellifera), Rueppell et
al. perform a comparative experiment among four colonies determining the
longevity of each colony’s worker bees.
The two colonies designated as large colonies are expected to exhibit
shorter longevity than the small colonies.
Honey bees are eusocial insects, which causes an interdependency of
individuals within the colony. Because
of this high degree of integration, a colony can be viewed as single organism. However, Rueppell et al. focus on the
individual worker bees and their roles within their respective colonies. They hypothesize that with higher numbers, worker
bees from larger colonies are more apt to perform more dangerous tasks to
collect food and are therefore more prone to earlier deaths. The loss of an individual worker bee in a
large colony is much less significant compared to a smaller colony based solely
on population ratios. For these reasons,
the expectation of higher longevity for worker bees in smaller compared to
larger colonies is a valid premise.
In order to test their
hypothesis, Rueppell et al. created four hives of European honey bees that
varied significantly in population size.
The experiments were conducted in Tempe, Arizona for three months from
May to July 2007. Two colonies had
approximately 4500 individuals, while the larger colonies had approximately
9000 individuals. These colonies were
allowed to persist in hives with glass walls in order to facilitate observation. For a control to the experiment, 400 and 800
worker bees were introduced to the small and large hives respectively along
with 796 tagged worker bees in each hive.
After introduction of the new worker bees, observations of hive
building, foraging, and longevity were recorded. Hive building was measured in square
centimeters of newly formed honey comb.
Pollen foraging was determined by the number of marked worker bees which
had pollen attached to their corbiculae (pollen baskets). Longevity was measured from the time of
worker bee introduction on the first day to each day thereafter. If a worker bee did not return to the hive,
they were presumed to have died.
Utilizing chi squared tests and
analysis of variance, Rueppell et al. were able to indicate that there was a
significant difference between the lifespans of worker bees in small colonies
compared to larger colonies. These
results were also graphically represented in survival (number of individuals)
over time (days of survival). [graph
included below] Small colony worker bees
were also able to collect more pollen, more efficiently than the larger colony
worker bees. Rueppell et al. were able
to confirm their hypothesis regarding comparative longevity in worker honey
bees. These results can be used to gain
further understanding of eusocial organisms and their roles with respect to
population size.
Graph: Longevity in honey bee workers cumulative survival
over age.
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