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Why are queen honey bees failing faster?

Beekeepers in the United States and Canada are now losing 25 to 40 percent of their honey bee colonies annually. A major cause of colony collapse is queen bee failure, which occurs when queen bees lose their ability to maintain the worker bee population. 

A team of researchers led by North Carolina State University set out to investigate why queen bees are failing faster than they did in the past. The experts found that when sperm viability is low, the expression of a protective immune protein is high.

According to study co-author Professor David Tarpy, the research has important implications for beekeepers and the farmers who rely on honey bees to pollinate their crops.

“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,” said Professor Tarpy.

Study lead author Alison McAfee explained that to have a healthy hive, honey bees depend on a healthy queen – the only female bee in a colony that can reproduce.

Early in life, the queen mates with many males and stores a lifetime supply of sperm in an abdominal organ called a spermatheca. 

As the sperm die out over time, the queen is unable to produce as many fertilized eggs and the colony’s population enters into a state of decline.

“Queens have the potential to live for five years, but these days, half the time queens (in managed honey bee colonies) are replaced within their first six months because they are failing,” said McAfee. “If a beekeeper is really lucky, a queen might live two years. Beekeepers need answers about why their queens are failing.”

“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.”

The researchers discovered that queen bees that were failing faster had significantly fewer sperm. Compared to those that were reproductively thriving, the failed queens tended to have higher levels of two specific viruses – sacbrood virus and black queen cell virus.

“The high levels of these viruses and poor sperm viability made us interested in seeing if there was a trade-off happening in the honey bee queen,” explained McAfee. 

“There’s a classical hypothesis in reproductive biology that you can’t do everything well, so there’s a trade-off between immunity and being able to reproduce. It’s been found in quite a few other organisms, including insects, that there are such trade-offs.”

The experts used mass spectrometry to compare the spermatheca of the healthy and failed queens. The analysis identified 2,000 different proteins, some of which were linked to sperm viability.

According to McAfee, one of the most important proteins linked to sperm viability was lysozyme, an enzyme that is part of the bees’ immune systems.

“The queens with the highest sperm viability had the lowest abundance of lysozyme, indicating that they weren’t investing resources in this kind of immune response,” said McAfee. “That supports this idea that there’s a trade-off between the queens being able to fight off infections and being able to maintain their stored sperm.”

Professor Tarpy said the research could help researchers find the cause of queen failure, which may ultimately help identify bad queens before beekeepers use them.

However, the exact cause of queen failure still remains unclear. “The underlying mechanisms could be disease. They could be pesticides. They could be improper nutrition,” said Professor Tarpy. “We don’t know, so we are working our way backward to identify the causes.”

The study is published in the journal Communications Biology.

By Chrissy Sexton, Staff Writer

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