Influence of Protein Surplus and Deficit on Worker Bees and Their
Colonies
Heather Mattila (PhD Student, Environmental Biology) and Gard Otis
My first two years of graduate work have concentrated on the influence
of protein availability on the ability of honey bees to overwinter.
Brood rearing ceases in colonies in late fall and the workers produced
at this time are long-lived "winter" bees that cluster within the
colony from late fall to spring. Winter bees are characterised by
hypertrophied fat bodies and hypopharyngeal glands, which are two major
locations of internal protein storage. Aside from internal worker
reserves, protein is also stored externally as pollen in the honey
comb. Over the winter, bees utilise these resources to provide protein
for the nutrition of developing larvae. A colony must begin rearing
young replacement bees in late winter in order to build colony strength
for the spring, long before adequate pollen foraging conditions exist.
When fall or spring pollen supply is limited, protein-starved colonies
will have to compromise the quality and/or quantity of the workers that
are produced for and by the overwintering population. Previous studies
have demonstrated that protein status plays an important role in the
ability of colonies to overwinter, but the influence of protein
availability on the development of the overwintering population and the
spring population that it produces remains poorly understood.
In my first field season, I examined the trade-offs made in the
production of spring workers by overwintered colonies that were
pollen-stressed (low pollen) or pollen-rich (high pollen) prior to
spring foraging. I estimated both the quantity (area of sealed brood)
and the quality (weight, size, asymmetry, total protein content,
longevity and nursing behaviour) of workers reared by these colonies in
the spring, as well as honey production in the following summer.
Colonies that had pollen supplements in early
spring produced two to four times more brood than control and pollen
restricted colonies, respectively, and only supplemented colonies
reared brood in significant amounts before natural pollen foraging
began (Figure 1). Although treatment did not affect weight, size or
asymmetry of workers, worker longevity was significantly affected:
workers reared in pollen-rich colonies lived an average of 15 days
longer than workers reared in pollen-stressed colonies. The survival
curves (Figure 2) show that, in general, a greater proportion of bees
reared under high pollen conditions were present in the observation
hive than bees from control or low pollen colonies. Longevity increased
even when workers experienced a common environment as an adult, which
means that differences were due to rearing conditions alone. Colonies
were unable to maintain worker quality at the expense of quantity, or
vice versa, but instead experienced a reduction in both. The earlier
and increased rate of rearing also translated into higher honey yields
by mid-summer, when pollen-rich colonies produced two times more honey
than pollen-stressed colonies. There was no difference in the
early behaviour of the bees, but the data suggest that workers from
pollen-rich colonies spend more time performing in-hive duties before
moving to outside tasks such as foraging. I am currently exploring
these possible differences in age-related behaviour.
The research that I am presently conducting is focused on establishing
a comprehensive understanding of the effect of pollen availability on
the size and timing of development of winter and spring populations by
following worker survivorship in pollen-manipulated colonies. This
study also includes quality and quantity comparisons for the
fall-produced winter population. I am conducting a complementary fall
study with marked workers in observation hives to determine the effects
of fall pollen availability on nursing and foraging, two critical tasks
that workers perform.