Researchers have long been stumped as to how honey bee populations continue to fall, with queen bees' reproduction capability unable to keep up. But a new study might help explain why.

A team from North Carolina State University in the US and the University of British Columbia in Canada published their work in the journal Communications Biology. Researchers detail their discoveries as to why queen bees fail, focusing on how low sperm viability leads to the expression of a protein - known to act against pathogens like viruses and bacteria - gets high.

Explaining Honey Bee Decline

This new research has significant implications for beekeepers and the farmers who still rely on honey bees to pollinate crops, according to David Tarpy, University Faculty Scholar and NC State Department of Entomology and Plant Pathology.

"Beekeepers have identified problem queens as a top management concern, but what's causing the problem is largely invisible. Queens go bad, and we don't know why," Tarpy said in a statement from NC State.

According to Alison McAfee, postdoc scientist at both NC State and UBC and lead author of the study, a healthy hive depends on having a healthy queen - the only female in the colony capable of reproduction. A queen honey bee reproduces with several male bees early in her life, later storing all collected sperm in an abdominal organ called the spermatheca. The storage and use of these sperms last for the queen's lifetime. When these sperms do not last long, it severely limits the queen's ability to produce fertilized eggs, leading to a decline in their population.

McAfee adds that queens generally live for up to five years. However recently, queens - mostly those managed colonies - are replaced within the first six months because they fail. 

"If a beekeeper is really lucky, a queen might live two years," the lead author added.

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Tracing Sperm Viability in Honey Bees

"The more we can find out about what is actually happening within these failed queens, the closer we can get to understanding why this queen failure is happening in the first place," McAfee adds.

To try and identify the problem, researchers discovered that queen bees failing to reproduce had much lower sperms compared to those that manage to continue reproducing, with a higher percentage of the sperms they have already died. Additionally, reproductively unhealthy queen bees were found to have more concentrations of viruses, specifically sacbrood and black queen cell virus. Researchers used a technique called fluorescent staining, showing which sperms were still alive and which were already dead.

McAfee explains that these two factors made them curious whether there was a trade-off happening instead, adding a classical reproductive biology hypothesis that there might be something in exchange for their deteriorating reproductive abilities. They used a mass spectrometer to better understand the insides of the spermatheca of the queen honey bees. Researchers found up to 2,000 different proteins, identifying which of them had something to do with sperm viability.

One of these proteins was lysozyme, a part of immune systems in animals, and that queens with high sperm viability had low lysozyme concentrations.


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