According to new research by University of Maryland entomologists, the lifespans of honey bees living in laboratory environments have decreased by about 50% over the last 50 years. It is hinting at possible causes for the industry’s troubling trends.
The study is the first to show an overall decline in honey bee lifespan that may be unrelated to environmental stressors. It was published today in the journal Scientific Reports. The findings suggest that genetics may be influencing issues such as increased colony loss and decreased honey production.
As bee colonies age and die off naturally, colony turnover is an accepted factor in the beekeeping industry. However, because of the higher rates over the last decade, beekeepers in the United States must replace more colonies in order to remain profitable. To figure out why, scientists have looked into environmental stressors, diseases, parasites, pesticide exposure, and nutrition.
Scientists modelled the effect of today’s shorter lifespans on beehives independent of environmental factors. The results matched real-world observations of US beekeepers.
“We’re isolating bees from colony life just before they emerge as adults. So, whatever is reducing their lifespan is happening before that point,” said Anthony Nearman, the study’s lead author and a Ph.D. student in the Department of Entomology. “The concept of a genetic component is introduced here.” If this hypothesis is correct, it may also point to a solution. We may be able to breed for longer-lived honey bees if we can isolate some genetic factors.”
Nearman noticed the decrease in lifespan while working on a study of standardised protocols for rearing adult bees in the laboratory with entomology Associate Professor Dennis vanEngelsdorp. In order to replicate previous research, the researchers collected bee pupae from honey bee hives. Then the pupae were within 24 hours of emerging from the wax cells in which they are reared. The collected bees were grown in an incubator before being housed as adults in special cages.
Nearman was testing the effect of supplementing the caged bees’ sugar-water diet with plain water to better mimic natural conditions. He noticed that the median lifespan of his caged bees, regardless of diet, was half that of caged bees in similar experiments in the 1970s-17.7 days now versus 34.3 days then. This prompted a more thorough examination of published laboratory studies from the previous 50 years.
“Because standardised protocols for rearing honey bees in the lab were not really formalised until the 2000s. You’d think that lifespans would be longer or unchanged, because we’re getting better at this, right?” Nearman explained. “Instead, the mortality rate more than doubled.”
A laboratory environment is very different from a colony. But historical records of lab-kept bees suggest that they have a similar lifespan to colony bees. Scientists generally assume that isolated factors that reduce lifespan in one environment will also reduce it in another. Research had also shown that shorter honey bee lifespans corresponded to less foraging time and lower honey production in the real world. This is the first study to establish a link between those variables and colony turnover rates.
The researchers simulated the impact of a 50% decrease in lifespan on a beekeeping operation. There, lost colonies are replaced annually. The resulting loss rates were around 33%. This is very similar to the average overwinter and annual loss rates reported by beekeepers over the last 14 years of 30% and 40%.
Nearman and vanEngelsdorp speculated that their lab-kept bees may have been exposed to low-level viral contamination or pesticides during their larval stage. This happened when they are brooding in the hive and being fed by worker bees. However, no overt symptoms of those exposures have been observed in bees. A genetic component to longevity has been observed in other insects such as fruit flies.
The researchers’ next step will be to compare trends in honey bee lifespans across the United States and other countries. If they discover differences in longevity, they can isolate and compare potential contributing factors. This includes genetics, pesticide use, and virus presence in local bee stocks.
