Date of Award
Spring 2024
Rights
Access is available to all users
Document Type
Thesis
Degree Name
Master of Science (MS) in Biology
Department
Biology
Abstract
Western honey bees (Apis mellifera) are important pollinators yet are threatened by a combination of factors such as poor nutrition, pathogens, parasites, and pesticide use. Bees encounter numerous pesticides while foraging (e.g. imidacloprid, a neonicotinoid insecticide) or in the hive colony (e.g. Tau-fluvalinate, a miticide commonly used to treat Varroa mite parasites). Similar to most organisms, the gut microbiome is important for bee health, metabolism, and behavior, however it is not well known how environmental factors like pesticides impact their gut bacterial symbionts. I hypothesized that 1) pesticide concentrations in bees are correlated with gut bacterial community structure, and 2) strain variation in growth response to pesticides exists within and among bacterial taxa. In this two-part study, I approached my hypotheses by combining field observations quantifying pesticides in bees and their gut bacterial communities (using LC-MS and 16S rRNA gene amplicon sequencing on Illumina MiSeq, respectively) in Chapter 1, and laboratory assays quantifying strain variation in the effects of pesticides on bacterial growth in Chapter 2. Field sampling of 20 hives across six sites in eastern Washington revealed that gut microbiome beta diversity and community evenness was significantly correlated with the concentration of imidacloprid (ng/g) detected in bees, but not with the other tested pesticides (Tau-fluvalinate, Cypermethrin). Thus, imidacloprid was the focus of laboratory assays in Chapter 2, where I tested isolates from core taxa, Lactobacillus mellis (n=25 strains), Bifidobacterium asteroides (n=15), and Snodgrassella alvi (n=10), against a range of imidacloprid concentrations (0-152.5 μg/mL) and measured OD600 over 24 hours. Most strains had significant growth reduction as imidacloprid concentration increased, but I identified significant phenotypic strain variation in the degree of growth reduction, with Bifidobacterium asteroides isolates having the largest strain variation. My strain variation results suggest that honey bee gut microbiomes, and likely other environmental and host-associated microbiomes, are more complex than may appear based on species-level taxonomy alone, and that environmental factors, such as pesticide exposure, may shape this “cryptic diversity.”
Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial-No Derivative Works 4.0 International License.
Recommended Citation
Mitchell, Macee R., "Field and laboratory evaluation of the interactions between pesticides and the gut microbiome in Honey Bees (Apis mellifera)" (2024). EWU Masters Thesis Collection. 940.
https://dc.ewu.edu/theses/940
