Bees are critical for our food systems and, until recently, have been largely taken for granted as pollinators who dutifully enable our crops and food systems to thrive. However, recently world-wide decline in bee populations have led to interest in bees and insects more broadly.
Factors contributing to bee population declines
Insecticides and habitat loss have likely affected bee populations; however, reasons for bee population declines are probably far more complex than only these reasons.
Insecticides and pesticides
Insecticides and pesticides, particularly neonicotinoids, are toxic to bees, affecting their ability to forage, reproduce, and resist diseases.
Habitat loss and fragmentation
Urbanization, deforestation, and agricultural expansion destroy habitats, reducing foraging resources and nesting sites. Fragmentation isolates populations, decreasing genetic diversity.
Climate change
Climate change alters floral resource availability, disrupting bees’ food supply. Extreme weather events further harm bee populations and their habitats.
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Disease and parasites
Diseases and parasites, like the Varroa destructor mite and deformed wing virus, weaken bees and reduce survival rates. Global trade exacerbates their spread.
Agricultural practices
Monoculture farming limits foraging options and disrupts bees’ natural cycles. The lack of diverse floral resources affects bees’ health and nutrition.
Pollution
Pollution, including heavy metals and pesticides, contaminates plants and flowers, posing risks to foraging bees. Air pollution affects bees’ ability to navigate and locate flowers.
Genetic factors
Inbreeding and loss of genetic diversity reduce bees’ resilience to diseases and environmental changes, making populations more vulnerable.
Monitoring bee populations with spatial science
Scientists are now using spatial science to monitor bees and map their populations. Local community efforts are also underway to encourage bee population recovery.
Estimating bee populations
Bee populations are very difficult to estimate. While in some global regions researchers have some knowledge of populations, in less accessible countries or regions knowing population numbers is difficult.
One of the most comprehensive estimates for bee populations was published in late 2020. By using verified observations, published records, and quantitatively comparing the results to occurrence data from public databases, scientists were able to create a global map of bee populations.
Results were also modeled to estimate distributions of bee populations from known data sets.
Global distribution of bee species
There are 6,340 species of bees estimated in the map; areas such as in Asia and Africa were under-represented due to poor quality of observations. On the other hand, North America and Europe are relatively well represented in data.
Overall, only 12% of countries have over 95% of their area sampled, with 15% having less than 5%. Even though data bias may limit some of the results, researchers found that North American, southern South America, southern Europe, Anatolia, Iran, parts of East Asia, and southern Africa among the most rich places for bee species.
Geography factors that affect bee populations
Additionally, researchers wanted to know what drove bee population distributions.
It was found factors such as solar radiation, mean seasonality (that is reduced overall seasonality), evapotranspiration, and mean continentality had among the most significant impact on population richness.
Areas with high solar exposure and good plant growth but also a good amount of moisture were among the best regions for bees. Even though moisture is important, even desert and Mediterranean weather regions were found to be rich in bee populations. Factors such as growing days and lower wind also seem to enable richer populations.
While more work is needed, particularly in tropical regions which are likely to also be important zones for bees, the work does show the importance of varied ecological zones for bee populations, particularly in temperate and warmer regions.[1]
Native bee species in the United States
In the United States, there are about 4000 native bee species. The United States Geological Survey (USGS) provides a bee inventory program called the USGS Native Bee Inventory and Monitoring Program.
This is an effort by the USGS to provide surveys for bee populations as well as plants that bees depend on. While the program does provide local and larger regional surveys, it also helps to provide tools and learning resources to help researchers and volunteers to identify bees.[2]
Organizations helping to protect bees
Given the threat to and importance of bees, groups have begun to emerge to help protect them.
In particular, urban areas have witnessed some of the greatest declines in bee numbers. Organizations such as Urban Bees bring people together to conserve bees.
In the case of Urban Bees, the organization creates mapping services that indicate where beekeepers can be found as well as people willing to help support bee populations. This helps communities and individuals plan on local conservation efforts by zones for bees where bees could potentially better thrive, including areas that can support diverse populations in mostly urban settings.[3]
Methods used to study bee populations
Given the small sizes of bees, most studies have used relatively intensive survey methods to collect samples of bees. Today, common methods include using Blue Vane traps, which are small plastic devices that attract bees using passive collection, to sample bee populations.
Using such sampling methods, researchers have been conducting seasonal and annual bee population monitoring. From research, it is likely that habitat loss, land-use change, and pesticides have impacted bee communities; however, research has also shown that in areas unaffected by these factors bee populations have also shown similar declining numbers in recent years.
Potentially, climate change could also be having an effect on habitat. Researchers show that biodiversity in bees can vary greatly due to seasonal factors as well as variations from year-to-year.
The future of bee population research and conservation
More work is likely needed to know exactly why bee populations have been generally declining in most regions that have been sampled over the last ten years.[4]
Mapping efforts and sampling have improved our understanding of bee species diversity globally. Identifying the factors influencing bee population diversity is crucial for addressing their decline. We now do have a better sense of key factors that seem to influence bee population diversity, but more work will be needed to pinpoint reasons as to why bee numbers have declined rapidly in places.
Continued research will be essential to mitigate the potential threats to global food production posed by declining bee numbers.
References
[1] For more on mapping global bee populations and factors that drive populations, see: Orr, Michael C. et al. 2021. ‘Global Patterns and Drivers of Bee Distribution’. Current Biology 31(3): 451-458.e4. https://doi.org/10.1016/j.cub.2020.10.053
[2] For more on the USGS Native Bee Inventory and Monitoring Program, see: https://www.usgs.gov/centers/eesc/science/native-bee-inventory-and-monitoring-lab.
[3] For more on Urban Bees, see: https://www.urbanbees.co.uk/.
[4] For more on bee population monitoring and population change during recent surveys, see: Turley, Nash E., David J. Biddinger, Neelendra K. Joshi, and Margarita M. López‐Uribe. 2022. ‘Six Years of Wild Bee Monitoring Shows Changes in Biodiversity within and across Years and Declines in Abundance’. Ecology and Evolution 12(8). https://onlinelibrary.wiley.com/doi/10.1002/ece3.9190 (October 9, 2022).
