The life expectancy of honey bees is 50% shorter than in the 1970s. As has been observed in laboratory samples, which would be potentially independent of environmental stressors and could have to do with some genetic reason.
The study published by Scientific Reports refers to the situation of these insects in the United States and points out that this decrease in longevity could explain the loss of colonies and the lower production of honey during the last decades in that country.
A team of entomologists from the University of Maryland focused on environmental stressors, diseases, parasites, pesticide exposure and nutrition to try to understand why this trend.
What did the study find?
The average lifespan of honey bees kept in a laboratory from the pupal stage has decreased from 34.4 days to 17.7 days in the last 50 years. As the bees in the study had not been exposed to any external environmental factors. This is believed to be the result of a genetic problem.
When the real-world effects of this reduced lifespan were modelled. It was found that it could result in colony mortality rates of around 33 per cent. This is similar to the 40 per cent annual mortality rate reported in the past 14 years by American beekeepers.
Other studies have linked the decreased lifespan of honey bees to reduced honey production and feeding times. Previous studies have focused on environmental factors, such as parasites, diseases, pesticides, and food availability.
However, the fact that scientists noted the shorter life span of bees who had never experienced this suggests that genetics play a role.
Nearman said: ‘We are isolating the bees from colony life just before they emerge as adults, so whatever is reducing their lifespan is happening before that point.’
‘This introduces the idea of a genetic component. If this hypothesis is correct, it also points to a possible solution.
‘If we can isolate some genetic factors, then maybe we can breed longer-lived honey bees. For the study, published today in Scientific Reports, Nearman and his colleagues attempted to replicate the standardized protocol for rearing adult bees, or Apis mellifera, in the laboratory.
Genetic factor of bees
The study shows an overall decline in honey bee lifespan potentially independent of environmental stressors or diet, ‘suggesting that genetics may be influencing broader trends observed in the beekeeping industry,’ the researchers noted.
The bees were isolated in a laboratory just before they emerged as adults, ‘so anything that reduces their lifespan is happening before that,’ said Anthony Nearman, the study’s lead author.
This circumstance introduces the idea of a genetic component. ‘If this hypothesis is correct, it also points to a possible solution. If we can isolate some genetic factors. We will be able to breed longer-lived honey bees,’ he added.
The researchers collected bee pupae from hives when they had 24 hours to emerge from the wax cells in which they were reared and finished growing in an incubator, after which they were kept as adults in special cages.
The half-life of bees in the laboratory was half that of similar experiments carried out in the 1970s. It currently stands at 17.7 days, compared to 34.3 50 years ago.
Although the environment of a laboratory is very different from that of a colony in nature. Historical records of bees kept in the laboratory suggest a similar lifespan to that of colonies. And scientists often assume that isolated factors that reduce the lifespan in an environment will also do so.
No symptoms of viral contamination
The authors considered whether laboratory bees might be experiencing some form of low-level viral contamination or pesticide exposure during their larval stage. When they are brooding in the hive and are being fed by worker bees.
But the animals did not show overt symptoms from those exposures. And it has been shown that there is a genetic component to longevity in other insects such as fruit flies.
The team will now compare the life trends of honey bees in the United States and in other countries. If differences in longevity are found. They can isolate and compare potential contributing factors. Such as genetics, pesticide use, and the presence of viruses in the populations of these animals.
Decline of bee populations
Declining honey bee numbers and health caused global concern due to the critical role of insects as important pollinators.
Bee health has been closely watched in recent years, as nutritional sources available to honey bees have decreased and pesticide contamination has increased.
In studies with animal models, the researchers found that combined exposure to pesticides and poor nutrition decreased the health of bees.
Reduced bee lifespan means reduced pollination. Bees and other pollinating insects are essential for a good harvest of 75 per cent of the crops we grow around the world. They also pollinate about 80 per cent of all wild plants.
Bees use sugar to fly and work inside the nest. But pesticides lower their sugar levels in the hemolymph (‘bee blood’) and therefore reduce their energy reserves.
When pesticides are combined with limited food supplies, bees lack the energy to function, causing survival rates to plummet.
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