Abstract
Honey bees (Apis mellifera) are important pollinators of plants, including those that produce nut, fruit, and vegetable crops. Therefore, high annual losses of managed honey bee colonies in the United States and many other countries threaten global agriculture. Honey bee colony deaths have been associated with multiple abiotic and biotic factors, including pathogens, but the impact of virus infections on honey bee colony population size and survival are not well understood. To further investigate seasonal patterns of pathogen presence and abundance and the impact of viruses on honey bee colony health, commercially managed colonies involved in the 2016 California almond pollination event were monitored for one year. At each sample date, colony health and pathogen burden were assessed. Data from this 50-colony cohort study illustrate the dynamic nature of honey bee colony health and the temporal patterns of virus infection. Black queen cell virus, deformed wing virus, sacbrood virus, and the Lake Sinai viruses were the most readily detected viruses in honey bee samples obtained throughout the year. Analyses of virus prevalence and abundance revealed pathogen-specific trends including the overall increase in deformed wing virus abundance from summer to fall, while the levels of Lake Sinai virus 2 (LSV2) decreased over the same time period. Though virus prevalence and abundance varied in individual colonies, analyses of the overall trends reveal correlation with sample date. Total virus abundance increased from November 2015 (post-honey harvest) to the end of the almond pollination event in March 2016, which coincides with spring increase in colony population size. Peak total virus abundance occurred in late fall (August and October 2016), which correlated with the time period when the majority of colonies died. Honey bee colonies with larger populations harbored less LSV2 than weaker colonies with smaller populations, suggesting an inverse relationship between colony health and LSV2 abundance. Together, data from this and other longitudinal studies at the colony level are forming a better understanding of the impact of viruses on honey bee colony losses.
Highlights
Honey bees (Apis mellifera) are eusocial insects that live in colonies composed of sterile female worker bees (~ 35,000), hundreds of male bees, and a single reproductive female, the queen bee [1]
To further investigate seasonal patterns of pathogen presence and abundance and the impact of viruses on honey bee colony health, we collaborated with a Montana-based commercial beekeeping operation that transports approximately 1500 honey bee colonies to California for almond pollination
Live honey bees were obtained for pathogen-specific Polymerase Chain Reaction (PCR) analysis of the prevalence of 13 pathogens: 11 commonly occurring viruses (i.e., acute bee paralysis virus (ABPV), black queen cell virus (BQCV), chronic bee paralysis virus (CBPV), deformed wing virus (DWV), Israeli acute paralysis virus (IAPV), Kashmir bee virus (KBV), Lake Sinai virus 1 (LSV1), Lake Sinai virus 2 (LSV2), Lake Sinai virus 3 (LSV3), Lake Sinai virus 4 (LSV4), and sacbrood virus (SBV)), and two eukaryotic pathogens (the trypanosomatid Lotmaria passim, formerly known as Crithidia mellificae sf (C.m./L.p.), and the microsporidial pathogen Nosema ceranae) (Nos.) [14, 26, 53, 54, 85] (S1 Table)
Summary
Honey bees (Apis mellifera) are eusocial insects that live in colonies composed of sterile female worker bees (~ 35,000), hundreds of male bees (drones), and a single reproductive female, the queen bee [1]. Honey bees are important pollinators of plants that produce fruit, nut, and vegetable crops, as well as numerous native and wild plant species [2,3,4]. It is estimated that insect pollination, primarily carried out by honey bees, is integral for the production of agricultural crops valued at $14.6 billion dollars annually in the US [5], and $175 billion dollars worldwide [2]. The majority of commercially managed honey bee colonies in the US (80% or over 1.8 million colonies) are transported to California to pollinate almond trees that produce over 80% of the global almond crop [6,7,8,9]. Longitudinal, colony-level monitoring studies that encompass almond pollination are required to better understand the impact of pathogens on high annual honey bee colony deaths in the US
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