Written by Lindsie M. McCabe & Theresa L. Pitts-Singer, USDA ARS Pollinating Insects Research Unit, Utah. May 5, 2022.
How can blue orchard bees help with pollination in cold springs?
The blue orchard bee (BOB: Osmia lignaria) is an effective solo or co-pollinator of orchard crops. This U.S. native, solitary, cavity-nesting bee is a proven pollinator of spring-blooming rosaceous crops including tart cherry, apple, and almond. Unlike honey bees, BOBs have only one generation per year and are adults for just four to six weeks annually. This foraging period can be manipulated to occur at any time between February and May using standardized management practices; thus, they can be made available to pollinate whenever bloom is expected to occur.
BOB adults overwinter in their cocoons and are eager to chews out as soon as warm temperatures arrive in the spring, which makes them particularly well-suited for early-blooming and/or high elevation orchard crops. BOBs forage in cool temperatures even when skies are overcast; honey bees can also fly at cool temperatures as long as there is sufficient sunlight. BOBs collect and carry pollen dry underneath their abdomen in coarse hairs (collectively referred to as ‘scopae’), and that pollen can easily transfer between flowers when the bees wiggle around floral structures to collect both pollen and nectar. Honey bee workers carry their pollen in tightly-packed pollen baskets (called corbiculae) and visit flowers for either pollen or nectar, meaning that they are less likely than BOBs to contact all the floral structures. BOBs zoom about the orchard among tree rows, while honey bees tend to more methodically visit flowers on one tree at a time.
“As early spring bees, BOBs are better adapted for flying under poor weather conditions than most other bees. BOBs forage and pollinate under overcast skies and at temperatures as low as 54°F (12C), when other bees are barely active. During good weather, BOBs also begin foraging earlier in the morning and end later in the afternoon.”
How to Manage the Blue Orchard Bee as Orchard Pollinator
-Jordi Bosch and William Kemp 2001
Highlights: BOBs in Washington cherries and pears (2019-2021)
Previous work in almonds has shown that nut set is increased when using BOBs and honey bees as co-pollinators. Therefore, we sought to determine if the use of BOBs + honey bees would enhance fruit set in Washington sweet cherries and pears. Indeed, the addition of blue orchard bees increased fruit set, but not harvested yield. Specifically, in 2019, 2020, and 2021, fruit set in cherry increased by 15% when BOBs were added compared to where honey bees were the only pollinators. In 2019 and 2021, pear fruit set increased by 5.5% with BOBs added. Furthermore, in 2 of the 3 years, the BOBs reproduced well in cherry orchards, often with the return of female bees as new progeny being >50% of the number of released females (Mattawa). BOB reproduction in pears was zero in where we worked in Dryden and Peshastin and low (20-50% female return as offspring) in a Yakima orchard. Nonetheless, the presence of BOBs still increased pear fruit set. Whether BOBs are similar to honey bees in their reluctance to visit pear flowers is not clear, and more work is needed to understand whether the crop itself, orchard management (e.g., pest/disease control applications), or microclimates cause blue orchard bees to fail to nest in pear orchards.
Blue orchard bees and honey bees work well together
We believe that co-deployment of BOBs plus honey bees could be done so that only half as many honey bees are needed per acre. A unique way to facilitate such a deployment is the use of a Hivetop Incubator (HTI). This patented invention creates a space atop an honey bee hive that houses BOB cocoons. Heat flows through the HTI’s screened bottom so that warmed BOBs chew out of their cocoons. BOBs exit HTIs through a small hole, fly away to mate and nest, and pollinate the crop. We added HTIs to hives along the edge of a WA cherry orchard, throughout which we provided BOB nesting materials. We found no negative effects on the honey bee colonies with HTIs added. The effects on BOBs were very positive. BOBs in hive-heated HTIs emerged 6× faster than bees in unheated HTIs. BOBs also nested evenly throughout the orchard and were not concentrated at the edge with HTIs. A honey beekeeper interested in the working with both bee species (possibly by partnering with a BOB manager/supplier) could benefit from this highly deployment effective tool.
Setups with each Hivetop Incubator (HTI)
Blue Orchard Bee (Osmia lignaria): Commercial Pollinator for Orchards. Theresa Pitts-Singer, Research Entomologist, USDA. Utah State Extension.
YouTube Video series on Utah State Extension Station
Why Blue Orchard Bees? https://youtu.be/-qbxbJ_d5pM
Playlist for management: https://www.youtube.com/playlist?list=PLMnDQoXFVBEbJ-uHZFxDMNsGHGdBw8jJt
Webinars/video from ICP Project on almond pollination and use of solitary bees
For commercially available bees and more BOB information, visit https://www.orchardbee.org/about-oba.
Lindsie M. McCabe, Ph.D.
USDA ARS Pollinating Insects Research Unit
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