Cattle Country: Grazing practices can increase bee abundances- methods for maintaining bee populations

Written by Michael Killewald and Jason Gibbs for the National Center for Livestock and the Environment (NCLE), University of Manitoba. It was originally published in Cattle Country in June 2024.

Insect populations across the globe are facing steep declines. Habitat loss by conversion of perennial pasture land to annual crop land, pesticides, and climate change have been identified as major drivers of these declines. This is problematic because insects provide many important roles to the environment, many of which often go unnoticed. Ecological functions such as pollination, decomposition, and pest regulation in particular help to support agricultural production as they directly increase crop yield and quality. Many insects pollinate crops, and bees are one of the most efficient pollinators because they must collect pollen to feed their young. Many common flowering crops are visited by bees, such as clovers, alfalfa, canola, flax, soybeans, and more. Although honey bees often are credited with pollination, other pollinators such as native bees are equal contributors and often superior to honey bees. Manitoba has a rich diversity of native bees. Recent research led by Dr. Jason Gibbs at the University of Manitoba has documented nearly 400 different bee species in the province and over 20,000 species have been identified worldwide. These native species face different threats than the non-native honey bee, which are primarily affected by the parasitic varroa mite. There is no doubt that bee populations in Manitoba need our attention, but how can we support them? Can livestock grazing practices be a part of the solution?

What do bees need?

Food, water, and shelter are among the basic requirements for animal survival, and bees are much the same. Pollen, nectar, and a suitable nest are the main requirements for bees. In addition, safety from predators and parasites is important. Land conversion has been the most damaging threat to pollinators, although any action that removes flowers (e.g. herbicides or mowing) can limit bees access to food. Destruction of nests often occurs by tilling or removing trees and shrubs. Most species of bees nest in the ground, but some nest in stems or logs.

Pasture land can support bee populations

Although large scale field crops are not very hospitable to bees, pastures can provide great habitat for bees. Research from Alberta has shown that canola fields with more pastures nearby contained four times more bumble bees and other bees than fields with fewer pastures in the surrounding landscape. Pastures often contain flowers that bloom from spring until fall and bees can use these as a food source. Additionally, pastures often contain a variety of shelter resources that bees can use to build their nests. Forested areas within pastures provide bees with nests both inside small holes in trees and places of undisturbed soil where ground-nesting bees can reside.

Research has shown that increasing the proportion of native, warm-season grasses can increase native bee abundance in pastures. Supplementing pastures with wildflowers may also benefit bees. Bees may be sensitive to the amount and type of grazing. Cows, sheep, and bison will all graze differently, and the extent of their grazing will affect how bees respond. Moderate levels of grazing are likely to be neutral or even beneficial for bees, particularly if flowers are not being removed.

Bee research at the University of Manitoba

PhD candidate Michael Killewald, working with Drs. Jason Gibbs and Alejandro Costamagna (University of Manitoba), conducted a multi-year sampling effort in pastures in southwestern Manitoba. The researchers found that many of the flowers identified from pastures are native prairie plants, such as: goldenrods, gumweed, purple prairie clover, blazing star, wild bergamot, and various sunflowers. These plants are attractive to a wide variety of species, including many specialist native bees, which restrict their diet to one or more of these plants. When Killewald collected bees on these pastures, he found that goldenrod, alfalfa, and sunflowers, all edible to cattle, were the most attractive to bees. Plants such as gumweed and bee balm were also highly attractive to bees, but are generally not consumed by cattle. According to this research, these are all plants that should be supported to conserve bee populations. Gumweed was the single most attractive plant to bees on grazed pastures—likely due to its abundance, as this was one of the most common blooming flowers encountered in the study. Other plants that could be included in pastures that are attractive to bees and are edible as forage include sunflowers and clovers.

Provide a home for bees

Bees are a diverse group of insects, and as such, different species require different nesting locations. Most species of bees tend to nest in the ground, so providing a small patch of sandy soil along a fence line gives a perfect location for bees to call home! A single scoop of sandy soil from a front-end loader placed along a fence line, or another location where it will not be disturbed, could be home to thousands of individual bees within a few years. Bees also find woodpecker holes or small stems to call home, but we can easily create “bee hotels” to recreate these conditions in managed ecosystems. Although pollinator-friendly nesting tubes are available for purchase, you likely have all the tools to create your own already! Simply take scrap pieces of wood, old pieces of firewood, or any piece of lumber, and drill holes of a variety of sizes and depths (3/16–½” wide and 2–6” long or 4–10mm wide 5–15 cm long). A variety of sizes is best so do not worry about making them perfect, the bees don’t mind. Place these in a location that is not flooded, and the bees will do the rest. Ideally, they are placed on a pole above the ground. Bees that nest inside these holes include the alfalfa leafcutter bee, a wild pollinator that has been commercially managed for alfalfa production using similar methods described above. Any effort, regardless of how small, will have a positive impact on increasing bee populations and ensuring the sustainability of both wild Canadian bee species and their associated pollination services.

For more information on bee research at the University of Manitoba and how you can help to enhance bee populations on your farm please contact Dr. Jason Gibbs or Michael Killewald.