Most species of wild bees are in decline in Europe, according to an analysis covering the last century

Is the study of good quality? Are the conclusions supported by sound data?

“This is a very high-quality piece of work, based on a very solid database. It brings together more than four million records, reviewed and validated by taxonomists and national experts. It spans a century (1921–2020) and covers 88 per cent of the bee and hoverfly species known in Europe, giving it a geographical and taxonomic scope that previous studies have lacked. Furthermore, the authors use occupancy models, which partly account for variations in sampling effort over time. They also test the robustness of their results with numerous sensitivity analyses. All of this makes the study and its methodology very robust".

How does this study fit in with existing evidence?

’The study confirms something that has long been suspected: that populations of many pollinator species are declining, and that this decline does not affect all species equally. Until now, most of the evidence came from a few countries in north-western Europe, such as the United Kingdom, Belgium and the Netherlands. This study shows that the pattern extends across the continent, although there are some regional differences. Patterns consistent with global warming are also evident. Bee species adapted to warmer climates are faring better than those from colder climates, such as many bumblebees. In the Alpine region, species that are expanding their range predominate, which is consistent with the colonisation of higher altitudes as temperatures rise.”

What is the current status of wild bees in Europe according to the study?

“The picture painted by the article is not particularly encouraging. Most of the bee species analysed have seen a decline in their range. In all regions, except the Alpine region, species in decline outnumber those on the rise. At a European level, the average range of bees has fallen by around 0.4 per cent per year, which equates to nearly a third over the course of a century. The good news is that no widespread extinctions have been observed on a continental scale; although specific populations may be affected, the vast majority of species have relatively recent records. This means there is still scope to reverse the trend if action is taken in time. It is a positive message that I think is also worth emphasising.”

Are there any significant limitations that need to be taken into account?

“The main limitation is the same as that faced by many of these studies that use existing databases, namely the geographical bias in the data, which is restricted to Europe and, within Europe, to specific areas. For example, the north-west of the continent, particularly the Atlantic region, is much better sampled than the south and east. Some regions could not even be analysed due to a lack of data. Furthermore, data from the first half of the 20th century are scarce and derive from opportunistic sampling, rather than systematic monitoring, and may reflect more limited taxonomic knowledge. For this reason, it was only possible to estimate trends for around 40 per cent of the species, which tend to be the most common ones.”

What are the implications?

“There are many implications. The decline of so many pollinator species may affect the reproduction of many wild plants in the area, as well as the production of crops that depend on pollination—such as many fruits and vegetables—which have been shown to require these wild pollinators despite sometimes being supported by honeybee hives. Furthermore, the replacement of vulnerable species by a few more resilient ones alters not only the species composition but also the range of functions these species can perform, which could lead to a decline in pollination services, even if the total number of species changes little. The results may help to update the IUCN Red Lists, particularly for species classified as ‘Least Concern’ or with insufficient data. They also reinforce the need for systematic monitoring programmes and policies for habitat protection and restoration.”

Is the study of good quality? Are the conclusions supported by sound data?

“Yes, the study is of good quality, very interesting, and the conclusions are supported by sound data. They have worked with a large number of records of pollinators, bees and hoverflies (hoverflies), and their methodology is sound, which supports their conclusions.”

How does this work fit in with the existing evidence?

“The study aligns with the widespread concern amongst experts and international organisations (such as the European Union or the FAO, for example) regarding the increasing decline of insects and, in particular, pollinators (especially bees) and its implications for biodiversity, the stability of terrestrial ecosystems, agriculture, global food supplies and, consequently, for us.”

What is the current status of wild bees in Europe according to the study?

“According to this study, the persistence of bee and hoverfly species at European level is relatively high, with species richness largely stable across all biogeographical regions, except for slight declines in the Atlantic and Continental regions, and recent increases in the Alpine region, although most bee species and approximately half of the hoverfly species experienced a decline in their range, with their characteristics having no influence, except for a slight negative trend in cold-adapted bees and more pronounced declines in parasitic species and food specialists.”

Are there any significant limitations that need to be taken into account?

“As this is a study covering the whole of Europe and the major biogeographical regions, the analysis does not go down to a medium or small scale, which homogenises different territories within the same region, as is the case, for example, on the Iberian Peninsula, which is bioclimatically and biogeographically very diverse, with more distinguishing factors than the authors consider to exist in the regions it is grouped with, and which therefore influence species richness. In fact, on the Iberian Peninsula, the high number of endemic bee species—as the authors point out—whose populations are in decline is not made clear; nor is it entirely clear why the study concludes that species richness in the Alpine region has recently increased, as this is a highly sensitive area with a large number of threatened species.

The final sentence of the press release should be clarified: what the authors of the study conclude is that most species persist at the European level and that regional species richness has varied only slightly; however, many specific species, particularly bees, have suffered substantial declines in their presence and population sizes, which is highly significant for their conservation"

What are the implications?

“The need for further studies in more restricted regions that complement and take into account local climatic variations—which influence regional distribution and diversity—using smaller-scale approaches, as well as the immediate implementation of the necessary and appropriate conservation measures.”