In a new study published today in the journal Scientific Reports, a duo of researchers at the University of Maryland found that the median lifespan of caged worker honeybees has been declining in the United States since the 1970s, from an average of 34.3 days to 17.7 days.
Colony turnover is an accepted factor in the beekeeping business, as bee colonies naturally age and die off.
But over the past decade, U.S. beekeepers have reported high loss rates, which has meant having to replace more colonies to keep operations viable.
In an effort to understand why, researchers have focused on environmental stressors, diseases, parasites, pesticide exposure and nutrition.
“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 lead author Anthony Nearman, a Ph.D. student in the Department of Entomology at the University of Maryland.
“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 honeybees.”
Nearman and his colleague, University of Maryland’s Dr. Dennis van Engelsdorp, first noticed the decline in lifespan while conducting a study on standardized protocols for rearing adult bees in the lab.
Replicating earlier studies, they collected bee pupae from honeybee hives when the pupae were within 24 hours of emerging from the wax cells they are reared in.
The collected bees finished growing in an incubator and were then kept as adults in special cages.
The authors then evaluated the effect of supplementing the caged bees’ sugar water diet with plain water to better mimic natural conditions.
They noticed that regardless of diet, the median lifespan of the caged bees was half that of caged bees in similar experiments in the 1970s.
This prompted a deeper review of published studies over the past 50 years.
“When I plotted the lifespans over time, I realized, wow, there’s actually this huge time effect going on,” Nearman said.
“Standardized protocols for rearing honeybees 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.”
Although a lab environment is very different from a colony, historical records of lab-kept bees suggest a similar lifespan to colony bees, and scientists generally assume that isolated factors that reduce lifespan in one environment will also reduce it in another.
Previous studies had also shown that in the real world, shorter honeybee lifespans corresponded to less foraging time and lower honey production.
This is the first study to connect those factors to colony turnover rates.
When the team modeled the effect of a 50% reduction in lifespan on a beekeeping operation, where lost colonies are replaced annually, the resulting loss rates were around 33%.
This is very similar to the average overwinter and annual loss rates of 30% and 40% reported by beekeepers over the past 14 years.
“Modeled colony lifespans allowed us to estimate colony loss rates in a beekeeping operation where lost colonies are replaced annually,” the researchers said.
“Resulting loss rates were reflective of what beekeepers’ experience today, which suggests the average lifespan of individual bees plays an important role in colony success.”
A. Nearman & D. van Engelsdorp. 2022. Water provisioning increases caged worker bee lifespan and caged worker bees are living half as long as observed 50 years ago. Sci Rep 12, 18660; doi: 10.1038/s41598-022-21401-2
This article was first published by Sci-News on 14 November 2022. Lead Image: Bee longevity, like any phenotypic expression, is the result of both environmental exposure and the bees’ genome. Image credit: Martin Tajmr.
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