|SLATER, GARETT - North Dakota State University|
|BOWSHER, JULIA - North Dakota State University|
Submitted to: Proceedings of the Royal Society B
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/27/2020
Publication Date: 5/27/2020
Citation: Slater, G.P., Yocum, G.D., Bowsher, J.H. 2020. Diet quantity influences caste determination in honey bees (Apis mellifera). Proceedings of the Royal Society. 287:20200614. https://doi.org/10.1098/rspb.2020.0614.
Interpretive Summary: Queen and worker honey bees have the same set of genes but develop into very different type of adults (castes) fulfilling different roles within the colony: the queen lays all of the eggs that the colony needs to provide for workers and future queens, whereas the workers are incapable of laying eggs and function to maintain the colony. Since the 1890’s it has been thought that the cause for this difference between queen and worker bees was the food they received during their immature stages, with queen-destined larvae receiving “royal jelly” and worker-destined larvae receiving “worker jelly.” Since that time, researchers have been looking for the substance within royal jelly that causes a larva to develop into a queen, but to date no such substance has been found. The Insect Genetics and Biochemistry Research Unit, Fargo, ND, in collaboration with researchers at the North Dakota State University, Department of Biology investigated a different mechanism of caste determination: whether it is the amount of food alone received during the larval stage and not some unknown substance that is responsible. Results from this study indicate that larvae receiving the largest amount of food developed into queens whereas larvae receiving the smallest amount of food turned into workers. Those larvae receiving an intermediate amount of food develop into adults with a mixture of queen and worker characteristics. This work not only suggests a significant change in the understanding of how queens and workers are determined, but it has commercial implications as well. For instance, trying to raise too many queens per colony runs the risk that the larvae would not receive enough food to fully develop into high quality queens.
Technical Abstract: In species that care for their young, provisioning has profound effects on offspring fitness. Provisioning is important in honeybees because nutritional cues determine whether a female becomes a reproductive queen or sterile worker. A qualitative difference between the larval diets of queens and workers is thought to drive this divergence; however, no single compound seems to be responsible. Diet quantity may have a role during honeybee caste determination yet has never been formally studied. Our goal was to determine the relative contributions of diet quantity and quality to queen development. Larvae were reared in vitro on nine diets varying in the amount of royal jelly and sugars, which were fed to larvae in eight different quantities. For the middle diet, an ad libitum quantity treatment was included. Once adults eclosed, the queenliness was determined using principal component analysis on seven morphological measurements. We found that larvae fed an ad libitum quantity of diet were indistinguishable from commercially reared queens, and that queenliness was independent of the proportion of protein and carbohydrate in the diet. Neither protein nor carbohydrate content had a significant influence on the first principle component 1 (PC1), which explained 64.4% of the difference between queens and workers. Instead, the total quantity of diet explained a significant amount of the variation in PC1. Large amounts of diet in the final instar were capable of inducing queen traits, contrary to the received wisdom that queen determination can only occur in the third instar. These results indicate that total diet quantity fed to larvae may regulate the difference between queen and worker castes in honeybees.