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What is causing bee populations around the world to decline, and what can we do to prevent future declines? Hint: there is a reason for hope and actions you can take to help.
However, how these products protect bee health and conservation is often questionable or even deceptive. Two biologists, Scott MacIvor and Laurence Packer, coined the term "bee-washing" in 2015 to describe these deceptive advertising practices that use unsupported bee- friendly claims or that promote misinformation about bee biology. Often, these claims focus on preventing honey bee decline but can also include erroneous claims regarding wild bee conservation.
Figure 1. Land use changes have resulted in habitat loss for wild bees. Left: A tall grass prairie with abundant wildflowers (Image: © Cassi Saari). Right: A monoculture corn field that is unsuitable habitat for bees (Image: © Richard Hurd)
If you have worked through the other modules in this program, you will have a strong background in bee biology and an ability to dispel many bee-related misconceptions. But you may still be wondering what you can do to help limit bee decline. This module will briefly cover the drivers of bee decline and what steps we can take to limit or even prevent future declines. After completing this module, students will be able to describe the major causes of bee decline and actions they can take to help.
There is not a single cause of bee decline. Instead, bees face a combination of many interacting threats, which reduce survival and reproductive success.
Bees need access to adequate floral resources and nesting sites for successful reproduction. The conversion of flower-rich habitats to monoculture farmland and urbanized environments reduces flower availability (Figure 1). Monoculture farmland can replace rich floral resources with wind pollinated crops and reduce the length of time during which there are flowers in bloom to just a few weeks. Habitat loss can have a particularly negative impact on specialized bees, which may lose access to the plant species they depend on for food. Clear-cutting forests and soil disturbance associated with land development also reduce the number of available nesting sites for cavity and ground nesting species.
Insecticides can lead to both lethal and sublethal effects in bees. While agricultural insecticides do not target bees specifically, it can be difficult to treat crops while limiting bee exposure. Certain insecticides persist in the environment, where wild plants can absorb them from the soil, potentially contaminating floral resources. Bees also risk environmental exposure from commercial and residential insecticides, some of which are explicitly marketed to kill ground and carpenter bees.
Other types of pesticides may also be negatively impacting bee populations. Herbicides reduce floral resource availability and floral diversity by aiding in the creation of large monocultures. Fungicides may also negatively affect bee populations; however, this is still an area of active research.
Many nonnative bee species have been introduced intentionally as agricultural pollinators and unintentionally through cargo shipments. These species are often free from natural enemies in their new range, introduce novel parasites and diseases, and outcompete native species. For example, the introduced species Osmia cornifrons can outcompetes native O. lignaria in the eastern United States, contributing to steep pop- ulation declines in the native species. A 2020 study by LeCroy et al. showed that while native species are declining, populations of O. cornifrons and the related invasive species, Osmia taurus, remain stable or are even increasing.
Figure 2. Osmia cornifrons was introduced to the United States as a spring orchard pollinator (Image: © Beatriz Moisset)
Another side effect of the introduction of nonnative species is the accidental introduction of parasites and diseases, placing highly susceptible wild bee populations at risk. Even today, we cannot fully mitigate the risk of spreading disease associated with transporting bees, even mason bees. It is challenging to avoid pathogen spread, but companies transporting or selling bees must exercise extreme caution to limit the spread of disease.
Warming temperatures and shifting weather patterns may reduce the availability of suitable habitat, cause disparities between bloom and bee emergence (see Life Cycle, Reproduction, and Development), and reduce foraging and nesting activity.
Wild bees face a multitude of threats, but there is hope! While corporations and the government are responsible for improving their practices and regulations to limit the impact of agriculture and development on bee populations, change at this level is often slow. However, there are actions you can take today to help maintain local bee populations.
You can increase local floral diversity in many ways. Perhaps the simplest option is to mow the lawn less often, every two weeks instead of every week. Lawns that are cut less often have a greater number of dandelions and clovers. While many people consider these species weeds, they are a valuable floral resource for many bee species.
Another option to increase local floral diversity is to plant a pollinator garden (Figure 3). When designing a pollinator garden, plant a variety of native species which bloom across the spring and summer and provide nesting sites (see next section). Do not replace native habitat with a pollinator garden; instead, build your garden in an otherwise unsuitable area for bees, such as areas with turf grass or nonnative weeds. For more information on pollinator gardens, see Activity: Design a Pollinator Garden in this module and the Xerces Society's guides (https://xerces.org/pollinator- conservation/yards-and-gardens).
Provide areas of bare ground for ground nesters near your garden, and avoid using thick layers of wood mulch, which can prevent nesting. For cavity nesters, provide stalks of hollow grass, branches of shrubs with hollow or pithy stems, and decaying tree branches and logs (Figure 4). Many perennial plant stems make great nesting material. Instead of disposing of all of your trimmed stems in the garbage or compost pile them up near your garden for bees to nest in.
You can also build or purchase bee hotels that provide nesting sites. If you decide to build or buy an artificial nesting structure, make sure your bee house has cavities of various sizes, which offer more nesting options for different species. Bamboo or drilled blocks of wood, without paper straw inserts, are difficult to clean, can harbor pathogens, and should be replaced after a season or two or avoided altogether. If you decide to purchase a mason bee hotel, look for nests built with reeds, grooved wood, cardboard tubes, or paper straws. It is not necessary to purchase mason bees for your nests, instead prioritize your local wild bees by providing a diverse selection of nesting materials. Remember, whether you purchase a bee hotel or build your own it must be maintained to limit the risk of parasite and disease spread.
Guidance on building and caring for a bee hotel: https://colinpurrington.com/2019/05/guide-to- diy-mason-bee-houses/
Guidance on what types of bee hotels to avoid: https://colinpurrington.com/2019/05/horrors-of- mass-produced-bee-houses/
Additional resources:
Free Resources for Educators
Residential pesticides can be harmful to bees. Avoiding insecticide and herbicide applications in your garden and yard will help protect bees from the direct and indirect effects of pesticides. Before reaching for a pesticide know that there are many alternatives available. If you have a question about reducing your pesticide use, your county extension agent may be able to guide you.
Protecting pollinators is a community effort. Raise awareness about bee diversity and decline and help dispel the common misconceptions surrounding bees. Get involved by telling friends and neighbors about the ways they can help support local pollinator health. Build a pollinator garden or make your yard more pollinator-friendly by mowing less, using fewer pesticides, and planting native species. Volunteer with organizations focused on land preservation and restoration. Create or participate in local or national pollinator protection initiatives and advocate for pollinator safe agricultural practices. Participate in citizen science projects like iNaturalist or The Great Sunflower Project. Even if you start small by sharing your knowledge of bee biology with friends and family, any action you take helps support pollinator health.
For more ways to get involved and to learn more about what you can do to help prevent pollinator loss, visit the Xerces Society's "Get Involved" page: https://xerces.org/get-involved.
Figure 4. Native bees benefit from varied habitats with many nesting opportunities, ample floral resources, and which are protected from contamination by pesticides (Figure: USDA NRCS).
The main threat facing bees is not Colony Collapse Disorder but a combination of several environmental and anthropogenic threats. Honey bees face fewer threats and lower extinction risk than native species.
Introduced species - A species which, as a result of human activity, is living outside of its native range.
Invasive species - An introduced species which causes harm to the local ecosystem, economy, or human health.
Habitat loss is one of the greatest threats facing bee populations. Building a pollinator garden creates a habitat for wild pollinators in your community.
When designing a garden, remember that pollinators need 1) floral resources, 2) nesting sites, and 3) building materials. In this activity, you will design a pollinator garden somewhere familiar to you, for example, your yard, a local park, or the school grounds.
Think about the area that you plan to build your garden. Consider what plants are already present and sun exposure. Choose a site that doesn’t already have native plants and will get enough sunlight for your plants.
1. Draw a map showing the location of your garden. Label any buildings, existing gardens, pavement, and natural areas.
When designing your garden, incorporate various plant types, including flowering trees, shrubs, perennials, annuals, and grasses. Plants should be densely planted and layered so that they receive the right amount of sunlight. Generally, it is best to plant shorter plants near the edges. Consider providing bare ground for ground nesting bees, old logs and branches, plants with hollow stems, a bee hotel, and other nesting resources (e.g., a small mud puddle for mason bees). Place nesting material where the morning sun will warm the bee nests.
2. Draw the layout of your garden. Where will you place plants of each type (tall vs. short plants, grass vs shrubs, etc.)?
3. Where will you place nesting habitat? Describe what this nesting habitat will look like.
The Xerces Society maintains a list of different pollinator-friendly native plant species for each region of the United States (https://xerces.org/pollinator-conservation/pollinator-friendly-plant-lists). Pollinator gardens benefit from a diverse group of plants that bloom throughout the year, from early spring through the summer. The plants you select can also provide nesting habitats for bees. Plants with hollow or pithy stems are great for small cavity nesting bees.
4. Use the Xerces Society guides to pick native plants for your garden. Make sure you choose plants that bloom at various times during the year and are all different sizes.
Now that you have a pollinator garden, you’ll have to perform some basic maintenance to keep it in good condition. Maintaining a pollinator garden is pretty simple. Pull any non-native weeds or unwanted plants which start to grow. Leave any plant material that collects in the fall. While it may seem dead, it provides shelter and a nesting habitat. Much of it will break down during winter, and what is left can be cleaned up in early summer. Don’t use pesticides in your garden. Finally, maintain your nesting habitat to limit disease.
5. Briefly describe how you plan to care for your garden. For example, think about how often you will weed and water. Do some plants need more water than others? What types of plant debris will you clean up, and what will you leave? How will you continue to maintain healthy nesting habitat?
Drivers of Bee Decline and What Can You Do Module PDF
Drivers of Bee Decline and What Can You Do Activity PDF
Goulson, D., Nicholls, E., Botias, C., & Rotheray, E. L. (2015). Bee declines driven by combined stress from parasites, pesticides, and lack of flowers. Science, 347(6229). https://doi.org/10.1126/science.1255957
LeCroy, K. A., Savoy-Burke, G., Carr, D. E., Delaney, D. A., & Roulston, T. H. (2020). Decline of six native mason bee species following the arrival of an exotic congener. Scientific Reports, 10(1), 1–9. https://doi.org/10.1038/s41598-020-75566-9
Lerman, S. B., Contosta, A. R., Milam, J., & Bang, C. (2018). To mow or to mow less: Lawn mowing frequency affects bee abundance and diversity in suburban yards. Biological Conservation, 221(December 2017), 160–174. https://doi.org/10.1016/j.biocon.2018.01.025
van Dyke, M., Boys, K., Parker, R., Wesley, R., & Danforth, B. (2020). Creating a pollinator garden for native specialist bees of New York and the Northeast.