Penn State Pollinator Webinar Series: Mason bee management for backyard and orchard pollination (Natalie Boyle)

Posted: July 7, 2020

Pollination by animals is essential for both agricultural and natural ecosystems. While honey bees provide the majority of managed pollination services, in this webinar the focus was on a different species of managed bees.

Dr. Natalie Boyle, an assistant research professor of entomology at Penn State University, discusses the biology and management of mason bees and their importance in the pollination of backyard and orchard habitats. Honey bees are a very popular and well-studied species - however, their lifestyle is not reflective of most bee life cycles. Of the 20,000 different bee species, over 70% are solitary. Female solitary bees must individually care for themselves and their offspring without any cooperation from other bees. Many solitary bee species live in natural above-ground tunnels, where females serially lay eggs into individual, partitioned cells. Mason bees exhibit this kind of life cycle which is distinct from the social lifestyle of honey bees. The name 'mason bee' comes from the fact that they collect clay and mud to build their nests.

Mason bees provide a variety of benefits to pollination services and landowners. As early fliers, they emerge in colder weather than other pollinators. These bees are also important in fruit, nut, and seed production because they specialize on agriculturally important tree fruit crops including pear, apple and cherry trees. Also, since these bees only live about 4-6 weeks they have a shorter foraging period, there are fewer opportunities for in-orchard pesticide exposure. Mason bees also provide economic benefits for orchardists because they are affordable and easy to maintain. These bees are also a wild pollinator that can be managed sustainably year after year. Unlike honey bees, there are no industry standards for caring for mason bees, which allows for creativity when choosing how to build and provide for your own population.

However, mason bees, like many other bee species, are still under threat. There are numerous challenges to bee health such as pesticides, parasites, pathogens, and climate change. These stressors may impact mason bees differently than honey bees because, as tunnel-nesting, short-lived adults, their life cycle is different. After adults emerge from their cell, the bees will mate and the female will seek out a nest and begin provisioning her offspring with pollen and nectar from flowers. They will often use tunnels already dug out by beetles, or available reeds or hollow stems to rear their young. After building a single cell, she will seal it with mud and begin forming the next cell. She will lay around 15 eggs in her lifetime. Inside the cell, the egg develops into a larva and will spend most of its time eating its provision mass of pollen and nectar, maturing into a pupa, and eventually an adult bee. Mason bees spend about 85% of their life cycle developing inside of their cell - for 10 ½ months - until the progeny undergo winter diapause and emerge as adults again the following spring.

In order to better support mason bees, Dr. Boyle suggests providing early spring-blooming flowers and trees such as redbud, Phacelia spp. wildflowers such as scorpionweed, maple trees, and oak trees. Having a large diversity of plants is better, as it provides bees with a diverse nutritional profile, and makes the local environment more attractive for them to nest at. Access to moist soil or mud is also essential for mason bees to build their cells, and is required for their reproduction. Landscape managers should also be thoughtful when considering pesticide use, as pesticides can have detrimental effects on bee performance and survival.

In addition to providing a favorable habitat, installing a bee hotel can also be very beneficial for mason bees. Bee hotels provide a premade habitat for cavity nesting bees and are readily available for purchase, or they can be homemade. They require active management, and special attention should be paid to their structure and design. Mason bees prefer a covered enclosure with 6" depth tunnels that are about ¼" in diameter. However, nest design and tunnel material may vary depending upon what bees nest in your area, so you can be creative in your design and try a few different things out to see what they like! No matter how you build your bee hotel, be sure that it is securely attached to a branch or post at an angle that maximizes sun exposure. If you are installing a bee hotel in your garden, it is best to catch your bees locally rather than purchasing them from trappers or other distributors. However, if you are using mason bees for commercial pollination, you will probably need to buy your bees, at least initially, to get the numbers required for your operation. When it comes time to release these bees it is best to wait until there is sufficient bloom. To avoid the threat of predators, Dr. Boyle suggests releasing mason bee adults and cocoons in a weatherproof, sealed container. You can easily make these yourself using readily available and inexpensive materials. Dr. Boyle recommends releasing bees in an enclosed 2" diameter, 8" across PVC pipe with a small exit hole drilled into one of the ends. This can easily be attached to a post or tree branch near the bee hotel. Once released they will begin mating, foraging, and reproducing. Once they have finished their reproductive cycle and laid all their eggs be sure to process and store your new bees over the winter until it is time to release them again the next season.

If you notice that your bees are not nesting, don't be alarmed. There are many reasons why bees may not be nesting in your area at a particular time. Every year brings its own challenges and it is best to be patient, especially when you have just started keeping mason bees. Try installing bee hotels in different locations or providing them with different flowering plants. The problem could also lie with the bees themselves. Getting bees from different suppliers or catching them yourself are great ways to get started learning more about the wild bees in your community. Keeping mason bees can be rewarding and sometimes challenging, so try not to get discouraged if nesting does not occur and work towards making the next season better than the last.

For more information about raising mason bees multiple resources will be linked below. Also, to learn even more about pollinator health be sure to sign up for the other webinars in this pollination series or look back on previous ones!

Written by Ashley Moak

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