In a paper published this week, a team of British researchers found that four bumblebee species they studied appear to have come under increasing stress from climate change over the past century. Stress appeared higher in the second half of the century, they found, tracking rising global temperatures and more frequent extreme weather.
To arrive at their results, the scientists measured the wings of thousands of bumblebee specimens collected over more than 100 years and housed in a network of natural history museums. Using digital cameras and special software, they looked for subtle asymmetries in the structure of the wing – a signal of environmental stressors that could affect bee growth and reproduction. They then compared their findings with historical climate data to find out if harsh weather conditions had made life harder for the insects.
According to the researchers, the warmer and more humid the weather, the more likely the bees were to develop unbalanced wings.
The findings suggest bees could face increasing threats as weather conditions deteriorate and global governments struggle to curb the carbon emissions that fuel climate change. The prospect of a further drop in bee numbers is a major concern as insects play a key role in pollinating wildflowers and crops, including food staples such as tomatoes, potatoes and vegetables. peppers.
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“This should reinforce the message that human contributions to high rates of climate change can affect wildlife in different ways, and we are putting these organisms at risk – which, in the case of bees, are crucial pollinating insects,” said Richard Gill, scientist at Imperial College London and co-author of the research paper, said. “They are incredible creatures that provide so many ecosystem services that we take for granted and essentially get for free.”
The study could also give researchers important tools to predict when and where bumblebees are most at risk, and help them make decisions about how best to protect them.
“The bottom line is really that there is a way to measure bumblebee stress, at least in a comparative way,” Richard Comont, scientific director of the Bumblebee Conservation Trust, a British conservation group, told The Post. “This opens up the possibility of comparing populations, and potentially different species, to decide on which to focus conservation efforts in the future.” Comont did not participate in the study.
Gill added: “This is essential for predictive modeling in the future, for targeting conservation efforts and for understanding which species are most at risk, and subsequently which plants and crops they pollinate are also at risk.”
Bumblebee populations have plummeted in the United States and Europe as the Earth has warmed. Research from 2020 found that the number of insect-populated areas dropped by 46% in North America and 17% in Europe. Places with steep declines also experienced dramatic climate changes, including higher temperatures and more intense heat waves.
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Gill’s team chose to examine the wing shape of bumblebees because a body of previous research has shown that other organisms – not just bees but also butterflies, lizards and rodents – can grow asymmetrically when under environmental stress. The phenomenon is called “fluctuating asymmetry,” and it has been observed in some animals when exposed to temperature changes, pesticides, infections, and other hazards.
The wings of bees in particular were useful to researchers because they could examine museum specimens without damaging them.
The team started by taking pictures of the bumblebees – more than 6,000 – with cameras fitted with macro lenses that allowed them to zoom in close without losing focus. Then they used software to tag the photographs with numbered coordinates that allowed them to accurately measure small but significant differences in the shape of the wings. For the year each specimen was collected, the team researched the average temperature and total rainfall, then compared the data.
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“That way, we could see if climatic conditions can contribute to the level of wing asymmetry,” Gill said.
“This showed that years that experienced relatively high temperatures had higher wing asymmetry, but this was particularly evident when there was also relatively high precipitation for such warm years,” he said. . In warmer, wetter years, he said, “bees showed the greatest wing asymmetry, which is an indicator of high stress during development.”
Gill said the team’s work showed how scientists could tap into museum collections to understand what’s driving population declines.
“They hold secrets,” he said, “which, when unlocked, can provide us with a great deal of information.”