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.