Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/13/2007
Publication Date: 1/4/2008
Citation: Schmid, M.R., Brockmann, A., Perk, C.W., Stanley, D.W., Tautz, J. 2008. Adult honey bees (Apis mellifera L.) abandon hemocytic, but not phenoloxidase-based immunity. Journal of Insect Physiology. 54:215-221. Interpretive Summary: Honey bee Colony Collapse Disorder is exerting tremendous impact on honey bee colonies. This is a devastating, yet poorly understood, crisis for commercial beekeepers and crop growers who depend on honey bees to pollinate their crops. The problem, however, may be related to an unknown disease or perhaps to impaired honey bee immunity to diseases. One approach to understanding the problem is to more thoroughly research honey bee immunology. With this goal, we are investigating the capacity for immunity in adult honey bees. In this paper we report on changes in honey bee blood cells, the cells that protect honey bees from infection. We show for the first time that adult queens, workers and drones naturally lose their hemocytes. This work with entirely healthy colonies indicates that loss of hemocytes is a normal aspect of honey bee immunology and not a feature of Colony Collapse Disorder. This new research will be directly useful to scientists who are working to understand honey bee immunology in detail. New knowledge on honey bee immunology potentially will benefit a wide range of agricultural producers by providing more insight into honey bees, their diseases and Colony Collapse Disorder.
Technical Abstract: Hemocytes and the (prophenol-) phenoloxidase system constitute the immediate innate immune system in insects. These components of overall insect innate immunity are present at any post-embryonic life stage without previous infection. Differences between individuals and species in these immune parameters can reflect differences in infection risk, life expectancy, and biological function. In honeybees which show a age-related division of labor within the worker caste, previous studies demonstrated that foragers show a strongly reduced number of hemoctyes compared to the younger nurse bees. This loss of immune competence has been regarded advantageous with respect to an already high mortality rate due to foraging and to redistribution of energy costs at the colony level. On the idea that abandoning hemocytes in all adults would be a reasonably direct regulatory mechanism, we posed the hypothesis that abandoning hemocytic immunity is not restricted to worker honey bees. We tested our hypotheses by performing a comprehensive analysis of hemocyte number and phenoloxidase (PO) activity levels in immunologically naive workers, queens and drones. We found that in all three adult phenotypes hemocyte number is dramatically reduced in early adult life. In contrast, we found the dynamics of PO activity levels have caste and sex-specific characteristics. In workers, PO activity reached a plateau within the first week of adult life, and in queens enzyme levels continuously increased with age and reached levels twice as high as those found in workers. PO activity levels did not change with age in drones. These data support our hypothesis, from which we infer that the previously reported reduction of hemocyte in foragers is not worker specific but represents a general phenomenon occurring in all honey bee adult phenotypes.