Most wild bee species analysed in a new European study, and about half of hoverfly species, have declined in geographic occupancy over the past century, according to research published in PNAS on October 19. Led by Spain’s Doñana Biological Station, part of CSIC, the work identifies conservation risks that apparently stable regional species totals can conceal.
The researchers examined more than four million validated records from 1921 to 2020, covering about 88% of Europe’s known bee and hoverfly species. According to the CSIC account distributed by SINC, statistical models assessed changes in species richness and geographic occupancy, alongside ecological characteristics and conservation status. Occupancy describes presence across sites, rather than a direct count of individual insects.
The study found losses in species richness in the Atlantic and Continental regions for both groups, while bees showed recent increases in the Alpine region. Lead author Carlos Martínez-Núñez said that unchanged species totals can mask substantial shifts within communities. Species can remain present somewhere in Europe while disappearing from parts of their former range.
Ainhoa Magrach of the Basque Centre for Climate Change told Science Media Centre Spain that the models partly correct for changing sampling effort. However, northwestern Europe has much better coverage than the south and east, and early records are sparse. Trends could be estimated for only about 40% of species, generally the more common ones, despite the database’s wider coverage.
The CSIC researchers warn that shrinking distributions could weaken pollination supporting ecosystems and crops. They identify habitat loss, fewer floral resources and pesticides associated with intensive farming as pressures, with climate change a growing threat. Magrach said the replacement of sensitive species by more resilient ones could diminish pollination functions even when the total number of species changes little.
Researcher Ignasi Bartomeus said in the CSIC account that limited continental extinctions so far leave room to reverse the declines. The team recommends conserving natural habitats, diversifying agricultural landscapes, maintaining flowers throughout the year and reducing pesticide use. The findings can guide future monitoring and conservation, while further research examines why species and regions differ.
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