Phenomic analysis of the honey bee pathogen-web and its dynamics on colony productivity, health and social immunity behaviors

Abstract

Many pathogens and parasites have evolved to overwhelm and suppress their host’s immune system. Nevertheless, the interactive effects of these agents on colony productivity and wintering success have been relatively unexplored, particularly in large-scale phenomic studies. As a defense mechanism, honey bees have evolved remarkable social behaviors to defend against pathogen and parasite challenges, which reduce the impact of disease and improve colony health. To investigate the complex role of pathogens, parasites and social immunity behaviors in relation to colony productivity and outcomes, we extensively studied colonies at several locations across Canada for two years. In 2016 and 2017, colonies founded with 1-year-old queens of diverse genetic origin were evaluated, which represented a generalized subset of the Canadian bee population. During each experimental year (May through April), we collected phenotypic data and sampled colonies for pathogen analysis in a standardized manner. Measures included: colony size and productivity (colony weight, cluster size, honey production, and sealed brood population), social immunity traits (hygienic behavior, instantaneous mite population growth rate, and grooming behavior), as well as quantification of gut parasites (Nosema spp., and Lotmaria passim), viruses (DWV-A, DWV-B, BQCV and SBV) and external parasites (Varroa destructor). Our goal was to examine: 1) correlations between pathogens and colony phenotypes; 2) the dynamics of pathogens and parasites on colony phenotypes and productivity traits; and 3) the effects of social immunity behaviors on colony pathogen load. Our results show that colonies expressing high levels of some social immunity behaviors were associated with low levels of pathogens/parasites, including viruses, Nosema spp., and V. destructor. In addition, we determined that elevated viral and Nosema spp. levels were associated with low levels of colony productivity, and that five out of six pathogenic factors measured were negatively associated with colony size and weight in both fall and spring periods. Finally, this study also provides information about the incidence and abundance of pathogens, colony phenotypes, and further disentangles their inter-correlation, so as to better understand drivers of honey bee colony health and productivity.

Land use changes associated with declining honey bee health across temperate North America

“…Additionally, estimates of infection and infestation levels from Varroa mites, gut pathogens and viruses provided data on potential confounding factors known to be associated with honey bee health. Detailed information on colony location, management and assessment protocols can be found in Borba et al (2022), so we provide only a brief overview of the methods used below.…”

“…All measurements were performed at the NWP National Bee Diagnostic Centre in Beaverlodge, Alberta. For specific details on pathogen sampling, isolation methods and quantification techniques, see Borba et al (2022).…”

Higher prevalence of sacbrood virus in highbush blueberry pollination units

“…At each time point, adult bees were sampled from an open brood frame into a 50 mL conical tube, placed immediately on dry ice, and transported to the University of British Columbia laboratory where they were stored at -70°C until all samples were collected. Bees were also sampled into a urine vial (∼120 mL, with an average of 260 bees per sample), which was then filled with 70% ethanol for conducting mite counts by the alcohol wash method as previously described (Borba et al 2022). Samples for pathogen analysis were shipped on dry ice to York University (Toronto, ON, Canada), where they were centrally stored at -70°C and then shipped to National Bee Diagnostic Center (NBDC) in Beaverlodge, AB, Canada.…”

“…All viruses were detected and quantified using RT-qPCR following sample preparation methods as previously described (Borba et al 2022). Briefly, total RNA was extracted from the second pooled sample of 60 bees using a NucleoSpin®RNA kit (Macherey-Nagel Gmbh & Co.), cDNA was synthesized from 800 ng total RNA using the iScript cDNA synthesis kit (Bio-Rad Laboratories), and reactions were assembled with sSoAdvanced™ Universal SYBR® Green Supermix (Bio-Rad Laboratories).…”

“…Here, we conducted an experiment evaluating twelve pathogens, which are among those most commonly observed in honey bee colonies (Evans and Schwarz 2011, Borba et al 2022), in colonies at different proximities to highbush blueberry fields in British Columbia. Colonies were placed in or near highbush blueberry fields (“near” sites) or at least 500 m away from blueberry fields (“far” sites) and sampled over time, starting immediately before the highbush blueberry pollination period and ending approximately two weeks after the pollination period.…”