Honey Hydrogen Peroxide as a Form of Social Immunity in Honey Bees (Apis mellifera) Open Access

Abstract

Social immunity involves cooperative mechanisms to defend against threats to colony health. For honey bees, this defense is critical given their deficit in immunity genes. I propose that honey hydrogen peroxide (H2O2) is a biochemical social immune factor that bees regulate to promote colony health and defend against pathogens. First, I tested in vitro whether experimentally adjusted concentrations of honey H2O2 affected the fitness of adult small hive beetle Aethina tumida (SHB). Results showed that pest survival was highest in the absence of honey H2O2 and was inhibited by higher concentrations. Second, I examined whether honey H2O2 content is spatially regulated in a healthy colony by measuring H2O2 content in samples from storage versus brood frames. I found that H2O2 concentrations were higher in brood frames suggesting that its defense role out weighs potential oxidative damage to brood. Third, I conducted a field study to examine whether supplemental feeding altered honey H2O2 content compared to nectar-fed controls. Results showed that high fructose corn syrup reduced honey H2O2 content while sucrose feeds increased H2O2 relative to control revealing that routine beekeeping feeds can modify the natural oxidant characteristics of colony honey. Fourth, I examined potential mechanisms by which supplemental feeding may alter honey H2O2, including feed concentration, induction of glucose oxidase (GO) activity by bee caste, and the statistical interaction between feed type and caste. I found that feed concentration did not alter H2O2 while bee caste GO induction was highest in receiver bees, and there was no statistical interaction between feed type and caste. Finally, I present two field studies in which colonies were infected with SHB and honey H2O2 content measured during infestation. The results showed positive, but not statistically significant, trends between colony infestation and honey H2O2. When supplemental feeding was a covariate, the infection-driven increase in H2O2 was reduced in fed versus unfed bees. This work is consistent with the hypothesis that honey H2O2 is a form of social immunity, which may be negatively impacted by supplemental feeding, a common beekeeping practice.

Table of Contents

Table of Contents

Introduction .........................................................................................................1

Chapter 1: Small hive beetle survival ....................................................................8

Methods..........................................................................................................9

Results...........................................................................................................10

Discussion......................................................................................................11

Chapter 2: Variation of honey H2O2 within the colony level...................................13

Methods.........................................................................................................13

Results...........................................................................................................14

Discussion.......................................................................................................14

Chapter 3: Effects of supplemental feeding on honey H2O2 ...................................16

Methods..........................................................................................................17

Results...........................................................................................................19

Discussion.......................................................................................................20

Chapter 4: Mechanistic drivers of the relationship between feeding and H2O2.......22

Methods..........................................................................................................23

Results ...........................................................................................................26

Discussion.......................................................................................................29

Chapter 5: Small hive beetle experimental infection...............................................34

Methods..........................................................................................................34

Results............................................................................................................36

Discussion.......................................................................................................38

References ............................................................................................................40

List of Figures .......................................................................................................45

About this Honors Thesis

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School	Emory College
Department	Biology
Degree	BS
Submission	Honors Thesis
Language	English
Research Field	Agriculture, Animal Pathology Biology, Entomology
Keyword	honey small hive beetle hydrogen peroxide social immunity honey bees antibacterial defense honeybee
Committee Chair / Thesis Advisor	Brosi, Berry J, Emory University
Committee Members	Beck, Christopher, Emory University De Roode, Jacobus, Emory University

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