The agricultural belt of the USA is in the midst of an environmental disaster. Populations of honeybees (Apis mellifera) that pollinate food crops in the USA and Europe are being decimated and there is no clear single culprit. Until recently, parasites, pesticides and climate change were thought to be the contributors to the insects’ demise, but now another factor is becoming apparent: malnutrition. ‘Most of the research focuses on adult bee nutrition’, says Ying Wang from Arizona State University, USA. However, little was known about the effects that malnutrition in early life could have on the adults. Starvation early in life is often detrimental, but it can prepare non-social animals, such as other insects, birds and mammals, for occasions when food is scarce when older. However, social bee larvae rarely experience starvation; they are usually reared in a stable environment with a reliable food supply. Could honeybees capitalise on the experience of shortages as larvae to prepare for times of scarcity when adults?
Teaming up with Osman Kaftanoglu, Wang isolated some of the wax comb – where the larvae develop – from the nurse bees so that the 5th instar larvae went unfed for 10 h before allowing the nurses to resume feeding their charges. Then, after the larvae completed development and emerged as adults, Wang measured the bees’ physical condition, how keen they were to feed and how well the adults survived over a 3 day period, while Colin Brent measured their hormone levels.
Collating the results, Wang found that although the bees that had been starved as larvae were initially smaller than those that had not been starved, they gained weight faster and after 6 days they were the same size as the bees that were well nourished. And the bees that had been starved during development survived better than the bees that had been well fed. Most surprisingly, the adult bees that had been starved while young coped better when food was scarce than the bees that had been well fed: ‘They had higher glycogen stores, were less sensitive to sugar (meaning that they were seeking higher quality food) and they had higher juvenile hormone levels, which is a hormone that helps them to respond to stress’, says Wang. The bees that had experienced deprivation during development were better prepared to survive starvation in later life, contrary to Wang's expectations.
But Wang and her colleagues Gro Amdam, Jacob Campbell, Robert Page and Jon Harrison were curious to find out whether the metabolism of bees that had been starved was permanently changed by the experience, or whether they would respond metabolically when challenged by famine. Collecting more adult bees that had been starved as larvae and measuring their metabolic rate while they were deprived of food, Wang and Campbell saw that the bees were able to reduce their metabolic rate, in contrast to bees that had not been starved as larvae. And when Wang measured their blood glucose levels, the bees that had been starved as youngsters maintained higher glucose levels than their sisters that had been well fed when young. The team also realised that the bees that had experienced larval starvation were better able to switch from using sugars for fuel to other materials, such as fats and proteins. So, the bees that had experienced starvation as youngsters had modified their metabolic response and survive starvation better as adults. Wang concludes, ‘Our studies present the first evidence that social organisms can have the ability to predict and adapt to future stress. Using this mechanism, we may be able to increase bee resistance to different stressors in the near future’.
