Honeybees are living half as long as they were 50 years ago

Honeybees kept under laboratory conditions in the US only live half as long as they did in the 1970s, suggesting that genetics could be contributing to colony losses, and not just environmental factors such as pesticides and sources of food.

Five decades ago, the median lifespan for a worker western honeybee (Apis mellifera) that spent its adult life in a controlled environment was 34.3 days. Now, the median is 17.7 days, according to research by Anthony Nearman and Dennis vanEngelsdorp at the University of Maryland.

The work began as an experiment looking at the effects of feeding plain water to lab-kept bees as a supplement, on top of their normal diet of sugar water. But through examining the scientific literature on similar studies over time, Nearman observed a downward trend in lifespan from the 1970s to now – which was reflected by the lifespan of the team’s caged bees. Paradoxically, mortality rates were found to have doubled since protocols for lab-rearing honeybees were formalised in the 2000s.

The change implies that solutions to the reduced life of colonies in the field, a problem increasingly encountered by beekeepers, may be found in the bees themselves.

“For the most part, honeybees are livestock, so beekeepers and breeders often selectively breed from colonies with desirable traits like disease resistance,” says Nearman.

“In this case, it may be possible that selecting for the outcome of disease resistance was an inadvertent selection for reduced lifespan among individual bees,” he says. “Shorter-lived bees would reduce the probability of spreading disease, so colonies with shorter lived bees would appear healthier.”

Despite the risk of trade-offs, the findings raise the possibility that if genetic factors influencing lifespan can be isolated, longer-lived honey bees could be specially bred.

Experimental honeybees are collected from hives as pupae within 24 hours of emerging from their wax cells, meaning that early exposure to pathogens or pesticides as larvae can’t be ruled out as a factor. However, the bees used in the current study showed no overt symptoms of such exposure, says Nearman.

Researchers started to document increasing rates of colony loss around 2006, after a phenomenon known as colony collapse disorder started killing huge amounts of colonies in the US. The disorder tailed off around 2008, but colony loss rates have remained higher than what beekeepers deem economically viable and the reasons why are uncertain.

The team’s modelling work demonstrated that a 50 per cent reduction in individual bee lifespan would result in an annual colony loss rate of 33 per cent — a figure that fits well with overwinter and annual loss rates of 30 and 40 per cent that have been reported by beekeepers.

Further research will look at lifespan trends across different parts of the US and around the world, in an attempt to compare the relative impact of genetic and environmental factors.

“This creative study highlights the importance of worker honeybee longevity in determining the overall health of a honeybee colony,” says Gene Robinson at the University of Illinois Urbana-Champaign.

“It does not identify the causative factors underlying the alarming decline in lifespan observed over the past 50 years, but provides a useful framework for considering how the well-known environmental stressors of pathogens, parasites, pesticides and poor nutrition interact with bee genetics to control lifespan,” he says. “As such, it makes an important contribution to our understanding of bee health.”