AUTHOR=Morfin Nuria , Foster Leonard J. , Guzman-Novoa Ernesto , Van Westendorp Paul , Currie Robert W. , Higo Heather 

TITLE=Varroa destructor economic injury levels and pathogens associated with colony losses in Western Canada

JOURNAL=Frontiers in Bee Science

VOLUME=Volume 2 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/bee-science/articles/10.3389/frbee.2024.1355401

DOI=10.3389/frbee.2024.1355401

ISSN=2813-5911

ABSTRACT=Varroa destructor is considered the main factor associated with winter colony losses. To control this ectoparasite, beekeepers must implement Integrated Pest Management (IPM) strategies. An effective IPM strategy is based on timely monitoring of mite levels to treat the colonies when the mites reach an economic threshold, and before they grow to damaging levels (economic injury level). Additionally, concerns have been raised about the possible interaction between V. destructor and other stressors; stressors acting additively or synergistically may lead to high colony mortality. The aim of this study was to record V. destructor levels in colonies from five regions of British Columbia, Canada: Lower Mainland, Kootenay, Okanagan, Cariboo, and Peace, and analyze them for associations with colony strength and mortality, and with other pathogens that were identified using total RNA sequencing. The Kootenay and Lower Mainland regions had the highest V. destructor levels in the fall (3.38±0.65 and 2.51±0.57, respectively) followed by the Okanagan (1.54±0.36), Cariboo (1.31±0.39), and Peace (0.66±0.25) regions. The Peace region had a significantly lower proportion of dead colonies than the other regions. Varroa destructor levels in the fall significantly predicted odds of colony mortality in the spring. Colonies with ≥ 1% mite infestation in the fall (August) had a significantly higher mortality rate (p=0.005) compared to colonies with <1% mite levels. Therefore, treatment is recommended above that threshold. Also, deformed wing virus-B levels were 8.4 times higher than those of the deformed wing virus-A variant in all regions. Lastly, Malpighamoeba mellificae and Nosema (Vairimorpha) apis transcripts were identified, along with other pathogens that deserve further investigation, including Lake Sinai virus, and Apis mellifera solinvivirus 1. The dynamic nature of host-pathogen interactions requires frequent pathogen surveillance to determine the prevalence and levels of parasitic mites and associated infectious diseases, and their impact on bee health, not only in the regions of this study, but globally. Nevertheless, more studies are needed to determine the nature of the type of interaction between the identified pathogens and V. destructor and their possible impact on colony survival to provide beekeepers with accurate recommendations for mite and disease control.