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In the United States, beekeepers faced unprecedented challenges last year, suffering a loss of over 55 percent of managed honey bee colonies— the highest rate recorded since the Apiary Inspectors of America began tracking these figures in 2011. A new study spearheaded by scientists at the University of Vermont, in collaboration with international partners, presents an innovative method for assessing hygienic behavior in honey bees, which may facilitate the breeding of more resilient colonies against diseases in the future.
“Beekeepers are losing bees at a rate that is simply unsustainable,” remarks Samantha Alger, director of the Vermont Bee Lab at UVM and the lead author of the research. “Back in the 1980s, annual colony losses were around 10-12 percent, but now the numbers have escalated to 30-50 percent. Such losses would be catastrophic for livestock farmers.”
Although honey bee populations can appear relatively stable due to the capacity of beekeepers to breed new bees, this process demands significant time, financial resources, and poses risks for native pollinators. Pathogens that affect managed honey bees can spill over into wild bee populations. Alger’s laboratory collaborates with beekeepers to cultivate strong, disease-resistant honey bee colonies, which can be marketed to both amateur and professional apiarists. A key aspect of their work involves helping beekeepers identify hygienic behavior, enabling bees to detect and eliminate unhealthy brood.
“It is much more beneficial for beekeepers to have bees with natural abilities to manage their health issues independently, rather than relying solely on chemical treatments, which can adversely affect the colonies,” Alger explains. “The challenge now is for beekeepers to accurately identify colonies that demonstrate robust hygienic traits. The UBeeO method offers a cutting-edge approach to test for this trait.”
Alger and her colleagues have evaluated a screening tool created by scientists at the University of North Carolina at Greensboro. This tool tests colonies for hygienic behavior by simulating the pheromones emitted by ill or deceased bees. Their research revealed that the UBeeO method can detect colonies that are resistant to various pests and pathogens, including Vairimorpha (more commonly known as Nosema) and different fungal infections, such as chalkbrood. Their findings were published in Frontiers in Bee Science on April 2.
“UBeeO has proven effective in identifying colonies better equipped to withstand Varroa mites, but it had not previously been employed to assess other pests or pathogens,” Alger notes. “Our latest findings indicate that this new assay can also pinpoint colonies resistant to these additional threats.”
Mechanism of Action
Visualize a thriving honey bee colony. Within the hive’s frames, a queen bee lays eggs into hexagon-shaped cells. As the eggs hatch, nurse bees nurture the larvae, sealing the cells with wax to protect them during development. Upon detecting that a bee is sick or deceased, nurse bees will uncork the cell and dispose of the pupa to ensure the health of the hive. This crucial action is known as hygienic behavior, heavily influenced by pheromones.
“Prior studies have identified death pheromones—compounds associated with deceased bees,” remarks Kaira Wagoner, a research scientist at UNC Greensboro and a co-author of the study. “E.O. Wilson was among the first to highlight this phenomenon, noting that oleic acid is released from dead ants. The same principle applies to bees, and these signals likely become stronger as the unhealthy brood decays within its cell. The cues from unhealthy brood are different and potentially more subtle compared to those of dead bees.”
Traditionally, hygienic behavior assessments for bees have revolved around measuring their response to dead brood. One well-known method, the freeze brood assay, involves applying liquid nitrogen to capped cells and observing whether bees will remove the dead pupae over 24 hours. In contrast, the UBeeO test takes a different approach.
“Instead of using liquid nitrogen to kill the developing larvae or pupae, we employ a blend of synthetic pheromones that replicate the chemicals released by sick or dying brood,” Alger clarifies. “This way, rather than assessing the bees’ capacity to detect dead brood, we’re evaluating their ability to recognize diseased brood, making this test more relevant to real-world scenarios.”
Wagoner, who co-developed the UBeeO tool during her doctoral research after isolating chemical compounds related to the odors of unhealthy brood, co-founded Optera, named for the honey bee order Hymenoptera, to offer UBeeO to beekeepers in the field. The technology became publicly available in 2024.
“This technology is in its infancy,” Wagoner observes. “We’ve tested it across more than ten different countries, and breeding programs have already been initiated in at least five locations, with much more data expected to emerge.”
Strength of the Investigation
The study evaluates UBeeO tests conducted in three geographical areas—Vermont, North Carolina, and Australia—to assess its effectiveness in identifying colonies resistant to pathogens. The UBeeO process involves spraying synthetic pheromones onto capped cells and monitoring nurse bees’ inspection behaviors for a two-hour window. The percentage of disturbed cells determines the UBeeO score. The team discovered that higher UBeeO scores correlate with reduced disease loads and specific thresholds for resistance against common honey bee pathogens.
“From our Australian data, we found that only a 13 percent response on the UBeeO test is needed for significant resistance to chalkbrood. In contrast, for resistance to Varroa mites, colonies need a response of approximately 55 to 60 percent,” explains Wagoner. “The bees’ responsiveness is influenced by the virulence of the disease affecting the brood. Chalkbrood is lethal to brood; hence, bees don’t need to be as vigilant in identifying it.”
Addressing Varroa mite infestations is more complex. These parasitic mites, which have been a threat to U.S. bee populations for about forty years, are known vectors of disease. They reproduce by laying eggs inside capped cells and feed off developing bees. If nurse bees fail to uncover an issue, Varroa mites may be released into the hive when a young honey bee emerges, underscoring the importance of hygienic behavior. By uncapping cells, bees can disrupt the mites’ life cycle.
The research also indicated that the UBeeO test could effectively identify colonies resistant to Vairimorpha, a disease impacting adult bees rather than the developing brood. This insight has sparked new inquiries into how hygienic behaviors function to mitigate Vairimorpha levels in honey bee populations.
“Understanding the mechanisms involved with Vairimorpha is somewhat enigmatic,” states Alger. “There may be additional actions taken by hygienic colonies that we have yet to discover.”
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