Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Dr. Graham J. Thompson

Abstract

The use of probiotics, particularly strains of lactobacilli, presents a promising strategy for addressing key threats to Apis mellifera, such as Varroa mites and Paenibacillus larvae. Lactobacilli are part of the honey bee hindgut microbiota, and some probiotic strains have been shown to enhance host immunity and buffer against pathogens. In addition, certain Lactobacillus strains can inhibit P. larvae growth, potentially preventing outbreaks. There is also some evidence that lactobacilli increase resistance against Varroa mites through immune system modulation or hive environment alteration. The objectives of this thesis were to: (1) review the complex interactions between P. larvae and other microorganisms within the bee gut microbiota; (2) perform an empirical study delivering probiotics to honey bee colonies across diverse landscapes. The field study revealed that oral administration of LX3 via protein patties significantly reduces mite infestations relative to a no-LX3 patty control across all environments, whereas topical spray applications do not yield the same success. This approach could serve as an environmentally friendly, sustainable method to improve bee health, crucial for maintaining ecological balance and supporting global agriculture.

Summary for Lay Audience

Honey bees, vital pollinators in the agricultural sector, are increasingly threatened by pests and pathogens, specifically Varroa mites, which are the number one cause of overwinter failure in Canadian beekeeping, and Paenibacillus larvae, the pathogenic bacterium that causes American foulbrood (AFB) disease. Beekeepers use increasingly sophisticated pest management strategies but with diminishing returns. There is therefore a sector-wide need for innovation in honey bee pest control and pathogen management. One approach, which I will refer to as microbial therapeutics, is to supply large numbers of bees within colonies a dose of living beneficial bacteria ('probiotics') that can potentially bolster the bee's immune and defense mechanisms. In this thesis I explore this idea in two ways. First, I present a review and deep synthesis of the literature to offer support and explore the limitations of using microbial therapeutics to control AFB. I conclude that there is a need to shift away from managing AFB strictly with antibiotics, and create a more sustainable approach, involving the integration of the entire microbial ecology associated with honey bees. Second, I conducted an empirical study that puts these ideas to the test. Specifically, I tested whether the supplementation of hives with lactobacilli, either orally through a patty or topically through a spray, in three different environments – agricultural, forage-rich and urban – could reduce their susceptibility to Varroa and P. larvae under the varied conditions that beekeepers might face. I found that the oral administration three-strain lactobacilli consortium (LX3) via the BioPatty helps to keep Varroa mite infestations low within treated colonies. It is noteworthy that the continuous use of a vehicle patty, which is common practice in commercial apiaries, increases Varroa mite infestations.

In total, my thesis highlights that carefully selected and thoroughly researched probiotic bacteria have the potential to mitigate honey bee pathogens. Their application can contribute to sustainable integrated pest management in the beekeeping industry. My research therefore contributes to pure and applied aspects of bee biology and suggests a new direction for managing bee health. Rather than targeting a single pathogen, we must address the entire microbial environment of bees, including all harmful microbes, to ensure a sustainable future for honey bees, the beekeeping industry, and crop pollination.

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