(ORDO NEWS) — The lifespan of laboratory-dwelling honey bees has shrunk by about 50% over the past 50 years, hinting at possible causes for worrying trends in beekeeping, according to a new study by University of Maryland entomologists.
The study, published today in Scientific Reports, is the first to show an overall reduction in honey bee lifespan that is potentially independent of environmental stressors. The results suggest that genetics may be contributing to problems such as increased colony loss and decreased honey production.
Colony turnover is a recognized factor in beekeeping as bee colonies naturally age and die. But the stronger numbers of the last decade mean that American beekeepers have to replace more colonies to keep production viable.
In an attempt to understand the reasons for this, researchers have focused on environmental stressors, disease, parasites, pesticide exposure, and nutrition.
However, when scientists modeled the impact of today’s shorter bee lifespan on hives regardless of environmental factors, the results matched real-life observations by American beekeepers.
“We isolate the bees from colony life just before they become adults, so anything that shortens their lifespan happens before that point,” said Anthony Nearman, PhD student in the Department of Entomology and lead author of the study.
“This suggests a genetic component. If this hypothesis is correct, it also points to a possible solution. If we can isolate some of the genetic factors, then perhaps we can selectively increase the lifespan of honey bees.”
Nearman noticed the shortened lifespan when he and Associate Professor of Entomology Dennis vanEngelsdorp conducted a study of standardized protocols for rearing adult bees in the lab.
Repeating previous studies, the scientists collected bee pupae from honey bee hives when the pupae were within 24 hours of emerging from the wax cells in which they were reared. The collected bees completed their growth in an incubator and then were kept as adults in special cages.
Nearman was evaluating the effect of supplementing the sugar-water diet of caged bees with plain water to better mimic natural conditions when he noticed that, regardless of diet, the average lifespan of caged bees was half that of bees in similar experiments in the 1970s – 17.7 days versus 34.3 days now.
This prompted a deeper review of published laboratory research over the past 50 years.
“Standardized protocols for growing honey bees in the lab weren’t formalized until the 2000s, so you’d think lifespans would be longer or not change because we’re getting better at it, right?” Nearman said. “Instead, we saw a doubling of the death rate.”
Although a laboratory environment is very different from a colony, historical records of bees kept in a laboratory show similar lifespans to bee colonies, and scientists generally assume that isolated factors that shorten lifespan in one environment will shorten it in another.
Previous research has also shown that, in the real world, a shorter lifespan for honey bees corresponds to less foraging time and less honey production. This is the first study to link these factors to the rate of colony turnover.
When the team modeled the impact of a 50% reduction in lifespan on a bee farm where lost colonies are replaced annually, they found that the loss rate was about 33%. This is very similar to the average winter and yearly losses of 30% and 40% respectively, reported by beekeepers over the past 14 years.
Nearman and vanEngelsdorp noted that the bees kept in the lab may have been exposed to some sort of low-level virus infection or pesticide exposure during their larval stage, when they hatch in the hive and the worker bees feed them.
But the bees showed no obvious symptoms of such exposure, and the genetic component of longevity has been found in other insects, such as fruit flies.
The researchers’ next step will be to compare trends in honeybee lifespan in the US and other countries. If they find differences in longevity, they can isolate and compare potential contributing factors, such as genetics, pesticide use, and the presence of viruses in local bee herds.
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