Date of Graduation

8-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Entomology (PhD)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Szalanski, Allen L.

Committee Member

Joshi, Neelendra K.

Second Committee Member

Steinkraus, Donald C.

Third Committee Member

Lee, Jacquelyn A.

Keywords

Apis mellifera; Genetic Diversity; Honeybee; mtDNA; Pathology; Pollinator health

Abstract

The western honey bee, Apis mellifera L., is a globally important pollinator plagued by several harmful stressors impacting colony health and survival. At least eight A. mellifera subspecies were imported and continue to be the genetic ancestors of U.S. honey bee populations today. Successive genetic bottle-neck events have led to reduced genetic diversity in U.S. honey bees. First, the subset of subspecies imported into the U.S. represents only a third of A. mellifera subspecies. Next, the parasitic varroa mite reduced managed and feral populations. Third, ongoing breeding practices have selected for traits from a single genetic lineage and bred from a limited stock of queens. Due to these genetic bottle-neck events, and limited access to outside germplasm, interest has arisen concerning increasing genetic diversity in U.S. honey bee populations.

Analysis of the mitochondrial DNA (mtDNA) in honey bees has allowed for genetic studies to characterize the origin of honey bee populations. Research has focused on commercial colonies, finding a limited pool of haplotypes from the Eastern European honey bee lineage. Research concerning the genetic diversity in non-commercial honey bee populations has been largely neglected. We studied the genetic variation of managed and unmanaged honey bee populations in the U.S., sequencing a portion of the mtDNA cytochrome oxidase I and II intergenic region. Molecular diagnostics were utilized to detect for seven pathogen species. Additionally, molecular and taxonomic techniques were used to explore a common colony pest’s identity and vector potential.

Haplotype diversity occurred among regions and between management types: a total of 43 haplotypes within four genetic lineages, ‘C’ (67.4%), ‘A’ (16.3%), ‘M’ (12.9%), and ‘O’ (3.4%); were detected throughout our study. We detected 20 haplotypes in unmanaged Utah honey bee populations, the majority of which (48%) were from the A lineage, suggesting African descent honey bees are common and diverse in Utah. In Arkansas, 25 haplotypes were detected in hobbyist-kept and unmanaged honey bee populations. Six commonly detected C lineage haplotypes accounted for 88% of the samples; however, 17 haplotypes from four lineages were detected in the remaining samples. Together, these findings suggest that hundred-year-old genetic remnants of historical importations have survived in feral honey bee populations despite the arrival of harmful stressors.

This study is among the first to comprehensively explore genetic origin, management, and regionality as factors of pathogen infection in U.S. honey bee populations. Honey bee pathogens Nosema sp., Lotmaria passim, and Varroa destructor were detected in all lineages, regions, and management types. All three pathogens were least prevalent in the A lineage, potentially due to African honey bees’ hygienic behaviors. Additionally, managed colonies exhibited higher mite loads compared to unmanaged colonies.

This study identified cockroaches sampled from Arkansas honey bee colonies as Parcoblatta sp. Additionally, Hymenoptera DNA was detected within the guts of the samples, indicating they likely fed on deceased bees. Nosema ceranae and L. passim were not detected in our samples, signaling further studies are necessary to understand the wood roach’s potential role in spreading honey bee pathogens.

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