According to a new study led by the University of Reading, warmer springs are causing bees in the UK to wake up earlier from hibernation, threatening the pollination of important crops such as apples or pears.
The experts found that, for each degree Celsius rise in temperature, wild bees emerge from their nests 6.5 days earlier on average. This could cause them to lose sync with the plants on which they depend and thus have less food to consume, meaning they may not have sufficient energy to pollinate crops effectively, or may even miss crop blossom completely.
“Rising temperatures are making life tougher for bees. Warmer conditions mean bees emerge from hibernation earlier, but there may not be enough food to provide energy for them when they start buzzing about,” said study lead author Chris Wyver, a doctoral student in Entomology at Reading.
“Matching wake-up dates with plant flowering is vital for newly emerged bees because they need to find pollen and nectar to increase their chances of survival and produce offspring. A mismatch means bees cannot pollinate effectively.”
“Less natural pollination could lead to farmers needing to use managed honeybees, meaning greater costs, which may be passed on to consumers. We could see even more expensive apples, pears, and vegetables in supermarkets as a result.”
By using over 350,000 individual recordings of bees emerging from hibernation, the researchers examined 88 different species of wild bees over a period of four decades in order to identify shifts in emergence dates, both over time and in relation to temperature changes.
The analysis revealed that, on average, the 88 species emerged four days earlier per decade, with some species emerging earlier than others (since different species of bees respond differently to changing temperatures). The results are published in the journal Nature Ecology & Evolution.
With winters projected to be one to 4.5 degrees Celsius warmer and up to 30 percent wetter by 2070, spring is likely to continue to start earlier and affect bees even more radically.
These shifts in bee emergence will have a major impact on plants that are heavily dependent on pollination, such as apple trees, which might not be ready to flower by the time bees emerge from hibernation.
To better understand how climate change affects the flowering of fruit trees and pollination by bees, the scientists have recently set up FruitWatch, a project encouraging people to report when fruit trees in their gardens and nearby parks start to flower.
Users’ submissions – of which over 6,500 have been received in two years – will help researchers build a larger and more reliable database documenting the impact of climate change on a variety of ecosystems.
Not all bees hibernate, but many do experience a period of reduced activity or dormancy during the colder months, which could be likened to hibernation.
In temperate climates, most species of bees are seasonal creatures that are most active during the warmer months of the year. As temperatures drop and food sources become scarce, many bees enter a kind of “winter rest.”
For example, honey bees do not hibernate in the traditional sense. Instead, they cluster together in their hives to stay warm, shivering their bodies to generate heat and feeding on the honey they collected during the warmer months. The queen is protected at the center of the cluster.
By contrast, bumblebees do experience a form of hibernation. The mated queens are usually the only members of the bumblebee colony to survive the winter, hibernating underground and emerging in spring to establish a new colony.
Many solitary bees, like mason bees and leafcutter bees, have a life cycle that involves a period of dormancy during the winter, but they spend this time as larvae or pupae in their nests, not active adults.
So while “hibernation” may not be the scientifically accurate term for all bee species, many bees do have adaptations to survive the winter in some form of dormant state.