Simko, ElemirWood, Sarah2023-08-1720232023-112023-08-17November 2https://hdl.handle.net/10388/14898European foulbrood (EFB) is an economically important disease in honey bees (Apis mellifera L.), caused by the bacterium Melissococcus plutonius. Honey bee larval infection by M. plutonius during environmental or nutritional stress results in decreased colony strength, honey production and pollination services, and increased management and treatment costs. Previously, outbreaks of EFB have been self-limiting, following the influx of abundant food resources during the summer months and recovery of the adult nursing bee population. More recently, outbreaks of EFB have been reportedly refractory to traditional management practices despite abundant food resources. Moreover, an abundance of these outbreaks have been reported during and following blueberry pollination. While it has been well established that strains of M. plutonius vary dependent on geographical location, and that fungicide products are commonly used during blueberry bloom, it is unknown whether pathogenic isolates of M. plutonius and fungicides used during blueberry pollination are risk factors for honey bee larvae developing EFB during and after blueberry pollination. To investigate the correlation between outbreaks of EFB and blueberry pollination, in Chapter 2, we described three clinical outbreaks of EFB in western Canada and characterized clinical isolates of M. plutonius using multilocus sequence typing and an in vitro larval infection model. We identified two different sequence types (STs) of M. plutonius (ST19 and a novel ST36), and both STs resulted in a significant decrease in larval survival compared to non-infected controls. To further explore the relationship between blueberry pollination and EFB, in Chapter 3, we expanded our M. plutonius surveillance across North America and compared the genetic STs and larval pathogenicity of M. plutonius isolates from colonies with and without a history of blueberry pollination. Of the 30 M. plutonius isolates we collected, we identified four different STs (ST12, 19, 21, and 27) and demonstrated that larval infection with 29/30 isolates resulted in a significant decrease in larval survival. Based on this study, a history of blueberry pollination was not correlated with M. plutonius pathogenicity or ST. Considering the absence of relationship between M. plutonius strain type and blueberry pollination, in Chapter 4, we explored whether larval exposure to fungicide products used during blueberry pollination may predispose honey bee larvae to mortality from EFB. While individual and combinations of two and three fungicide products did not decrease larval survival from EFB, honey bee larvae that were infected with M. plutonius bacteria and subsequently exposed to four fungicide products simultaneously had a significant decrease in survival compared to infected controls. Taken together, our examination of the environmental and pathogen determinants of EFB revealed that colony exposure to the combinations of four fungicide products may be a potential driver of EFB during and after blueberry pollination; however, further verification of these findings using colony-level studies is necessary. Moreover, this research highlights the importance of collaboration amongst various stakeholders, including veterinarians, beekeepers, blueberry growers, bacteriologists, and agronomists, to support honey bee health during blueberry pollination and contribute to the ongoing investigation of the disease ecology of EFB.application/pdfenEuropean foulbroodhoney beesblueberriesThesis2023-08-17