UNDERSTANDING HONEY BEE COLONY MORBIDITY AND MORTALITY THROUGH PHYSIOLOGY AND LIFESPAN

Abstract

Managed honey bee colonies (Apis mellifera) are a critical component of our agroecosystem. As such, we need to understand and address risk factors that contribute to colony loss. Fundamental to this understanding is a need to detail the connection between individual bee’s physiology, life histories, and colony fitness. In this dissertation I first present an in-depth review of honey bee physiologies important for colony success (Chapter 1); I then examine standard methods for rearing honey bees in a laboratory setting and the importance of individual bee lifespan on colony loss (Chapter 2); followed by identification of honey bee physiologies that relate to chronological age as a means of measuring colony demographics and health (Chapter 3); and then apply potential age- and disease-related physiology measures to determine associations with overwinter colony loss and known and unknown risk factor exposure (Chapter 4). Research indicates honey bee colony loss is largely driven by poor nutrition, pesticide exposure, and parasites and the viruses they vector. Management practices and techniques to mitigate the effects of these risk factors decrease loss rates but do not prevent all of them. New knowledge, therefore, is needed to address the gap in knowledge between risk exposure and colony mortality. As a honey bee colony is a complex interaction between multiple groups of individual bees, collective physiological changes among these groups hold promise for understanding why some colonies die while other do not when exposed to the same risk factors. In one experiment (Chapter 2), I demonstrate the importance of access to water on honey bee lifespan. In a literature review informed by the data obtained from these experiments, I discovered that the median lifespan of laboratory specimen has decreased by half over the past 50 years and that this change is predictive of overwinter loss rates reported by beekeepers since 2006. If the age of individual bees can affect the lifespan of a colony, I posited that physiological measures predictive of individual bee age could be useful to ascertain the demographics of a colony’s population, which would in turn be a measure of colony health. To test this hypothesis, I built upon previous physiology studies and examined age-linked cohorts of bees through the fall transition to overwinter. In doing so I derived a set of easily identifiable physiological measures either predictive of individual bee age or a possible unidentified disease state. I then applied these measures to a retrospective cohort study, where I was able to determine that changes in the prevalence among several physiologies were associated with overwinter mortality and known risk factor exposure. These methodologies and results show promise for the use of physiological measures as a potential pragmatic tool to predict colony survivorship, to diagnose past known and unknown risk factor exposures, and to further advance fundamental knowledge of the role demographics play in societal health.