Bumblebees Increasingly Stressed by Climate Change Over Past 100 Years, Study Finds

A bumblebee collects pollen from lavender flowers
A bumblebee collects pollen from folgate lavender flowers at Scottish Lavender Oils at Tarhill Farm, Kinross on July 20, 2022. Jane Barlow / PA Images via Getty Images
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Bumblebees are larger than honeybees and, while they collect and store nectar from flowers to consume themselves, they do not convert nectar into honey like honeybees. Bumblebees are essential pollinators for many wildflowers and agricultural crops like sunflowers, cranberries, blueberries and tomatoes.

Two contemporaneous papers examining bumblebee populations in the UK were recently published by scientists from the Natural History Museum and Imperial College London.

In one of the studies, conducted by a network of museums in the UK, scientists linked signs of stress in bumblebee wings to the progressively hotter and wetter conditions of our changing climate, stated a press release from The Natural History Museum, London.

The findings, “Signatures of increasing environmental stress in bumblebee wings over the past century: Insights from museum specimens,” were published in the Journal of Animal Ecology.

Recently, insect pollinators such as bumblebees have faced sharp population declines due to the higher temperatures associated with climate change, the excessive use of toxic agricultural chemicals, intensive farming and lack of crop rotation.

Using ancient DNA techniques usually used for studying ancient humans and wooly mammoths on insects for the first time, the researchers sequenced the genomes of bumblebees going back more than a century in order to demonstrate past stressors for bees.

The study can also be useful in forecasting potential future causes of stress, as well as possible prospective population declines, the press release said.

The researchers took specimens of four UK bumblebee species going as far back as 1900 and examined their body shapes using digital images. The researchers found asymmetry in the shapes of the bumblebees’ wings to be indicative of stress. Stark differences in the shape of each wing meant that the bees had been exposed to stressors during their development.

The researchers found that the lowest evidence of stress for the bees occurred around 1925, but that the bees’ stress levels increased as the century went on. They also found evidence of a persistent higher level of stress for the bees in the second half of the century.

“By using a proxy of stress visible on the bee’s external anatomy and caused by stress during development just days or weeks before, we can look to more accurately track factors placing populations under pressure through historic space and time,” said study author Aoife Cantwell-Jones from the Department of Life Sciences at Imperial College London in the press release.

When the researchers looked at the yearly rainfall and mean temperature during each collection year, they found that in years that were wetter and hotter, the asymmetry of the bees’ wings was more distinct.

“With hotter and wetter conditions predicted to place bumblebees under higher stress, the fact these conditions will become more frequent under climate change means bumblebees may be in for a rough time over the 21st century,” said senior author of the study Dr. Richard Gill from the Department of Life Sciences at Imperial College London, according to the press release.

In a concurrent study, scientists from the Natural History Museum and the Earlham Institute used more than 100 bumblebee specimens from the museum going back more than 130 years in order to sequence their genomes.

The findings of the second study, “First large-scale quantification study of DNA preservation in insects from natural history collections using genome-wide sequencing,” were published in the journal Methods in Ecology & Evolution.

In this study, the scientists used one bee leg from each of the bee specimens to measure the amount of DNA that had been preserved in order to find out how stress may cause loss of genetic diversity.

The researchers will use the information to examine how the genomes of bees have evolved in order to learn whether populations of bees have acclimated to changing environmental conditions.

“Our goal is to better understand responses to specific environmental factors and learn from the past to predict the future. We hope to be able to forecast where and when bumblebees will be most at risk and target effective conservation action,” said Dr. Andres Arce of the University of Suffolk, who contributed to both papers, as The Guardian reported.

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