Striking research from a pair of entomologists at the University of Maryland suggests the lifespan of honey bees kept in controlled laboratory conditions is 50% shorter than what was seen in the 1970s. The researchers hypothesize genetic changes in bees may be responsible for the shorter lifespans.
Studying the lifespan of honey bees can be challenging. In real-world conditions the lifespan of a worker bee can vary depending on the dynamics of its specific colony. Our general understanding of bee longevity stem from several key studies conducted in the 1950s, with scientists tagging bees before returning them to wild colonies for observation.
Around 50 years ago scientists began to conduct more controlled bee studies, tracking lifespans in caged laboratory environments. While these experiments don't correlate with real-world experiences they can serve as valuable standardized insights into bee lifespans, not confounded by other environmental variables.
The new research began when entomologists Anthony Nearman and Dennis van Engelsdorp were conducting a study looking at how sugar in water affected the lifespan of caged bees. The researchers noticed the median lifespan of bees in their studies was half of what was reported in similar studies from the 1970s.
The researchers replicated all the protocols from older studies. Bee pupae was collected from hives before they emerged and then kept in similar caged conditions as adults. But their modern bees were only living a median of 17.7 days compared to the 34.3 day lifespan reported in the older studies.
“When I plotted the lifespans over time, I realized, wow, there’s actually this huge time effect going on,” said Nearman. “Standardized protocols for rearing honey bees in the lab weren’t really formalized until the 2000s, so you would think that lifespans would be longer or unchanged, because we’re getting better at this, right? Instead, we saw a doubling of mortality rate.”
The researchers do indicate there is a recent body of study indicating bee lifespans have decreased over the past few decades. However, that research has primarily focused on real-world conditions, encompassing environmental stressors such as disease and pesticide exposure. This new research is the first to eliminate all those variables and suggest there could be a decline in honey bee lifespan independent of environmental factors.
“We're isolating bees from the colony life just before they emerge as adults, so whatever is reducing their lifespan is happening before that point,” said Nearman. “This introduces the idea of a genetic component. If this hypothesis is right, it also points to a possible solution. If we can isolate some genetic factors, then maybe we can breed for longer-lived honey bees.”
University of Sussex biologist Dave Goulson called this new study "fascinating" but points out a number of caveats making its conclusions far from definitive. He suggests comparing current experiments to historical data from up to 50 years ago is difficult as there is no guarantee lab conditions are similar between such disparate eras. Goulson also speculates its possible pesticides have infiltrated the pollen being fed to larvae, affecting the bees' lifespan from this early point.
Nevertheless, Goulson does indicate these results need to be taken seriously because if they are correct, "something really worrying is going on." He notes similar examples of natural selection favoring shorter lifespans may be occurring in other species.
"Artificial (by beekeepers) or natural selection may favor bees with shorter lifespans," Goulson writes in The Conversation. "Scientists are seeing this happen in other species. For example, cod now mature earlier and when they are smaller in size because overfishing means fish rarely survive long enough to grow large. Perhaps stressors in the modern world, such as pesticides and disease, mean honey bees rarely survive for a long time. So their evolution might favor a live-fast-die-young lifestyle."
Nearman and van Engelsdorp are very aware their hypothesis honey bees are experiencing shorter lifespans due to genetic changes is still incredibly speculative. It's even possible that beekeepers have inadvertently simply favored colonies with shorter lifespans due to a perception of better health.
So the next step for the researchers is to widen their scope and look at honey bee lifespans in different geographical regions. If they still detect consistent patterns of decreased longitivtiy then genetic studies can attempt to home in on what exactly is going on.
The new study was published in Scientific Reports.
Source: University of Maryland
