California almond growers have always relied heavily on honeybee hive rentals to pollinate their orchards. Responsible for 80% of global almond production, these growers are highly dependent on obtaining healthy honeybee colonies from contracted commercial beekeepers.
With a record 1 million almond-bearing acres forecasted for this year’s harvest, meeting the growing pollination demands of the industry may become increasingly more difficult for migratory beekeepers. On average, they have sustained annual losses of one-third of their hives each winter and struggle to mitigate challenges associated with mite pressure, pathogen transmission, pesticide exposure, and nutritional limitation.
Since its inception in 2012, researchers associated with the Integrated Crop Pollination (ICP) project, funded by a five-year USDA Specialty Crop Research Initiative grant, have been working towards identifying management practices that can provide improved support for almond pollination in California. In particular, they are investigating the use of an alternative bee, the blue orchard bee (BOB), to assist honeybees with meeting the intense the pollination demands during almond bloom.
The BOB is a commercially available cavity-nesting bee that preferentially forages on spring-blooming orchard crops. Unlike honey bees, BOBs are not social and do not live in a hive or make honey. They are a solitary species, in which each female mates and forages for provisions for her offspring alone.
They have one generation per year, and are free-flying adults for only a few weeks of that year. Most of their life is spent as adults in individual cocoons. This is also known as diapause, which is essentially an insect hibernation.
BOBs’ Pros and Cons
BOBs are a popular pollination choice for many orchard producers and have been implemented successfully in almond, apple, cherry, and pear orchards. Part of what makes them appealing for so many cropping systems is their activity can be carefully timed to align with bloom by manipulating standardized storage incubation practices.
ICP researchers think BOBs could offset potential shortages of hives in meeting future pollination needs. In fact, previous research has shown when BOBs co-pollinate orchards with honeybees, growers see significantly improved almond fruit set, and sometimes, nut yield.
Unfortunately, the biggest challenge in relying on BOBs as pollinators is their limited supply. Sustainable in-orchard reproduction of BOBs in commercial orchards for use during the following year is not always achieved, and limited by BOB dispersal away from the orchard upon their initial release. Most BOBs available for distribution at this time are captured from the wild, which may have repercussions on native populations and their contributed ecosystem service to unmanaged environments.
Additionally, trapping bees is labor-intensive, and management practices for the processing and cleaning of cocoons to eradicate pests and disease is expensive. Thus, current retail costs of BOBs for commercial pollination greatly exceeds costs associated with hiring traditionally relied- upon honeybee colonies.
In-orchard propagation of BOBs offer the best solution to the supply problem, and previous work of some members of the ICP team have refined best management practices for the distribution of nesting sites and points of release for orchard pollination. Researchers have also developed a chemical attractant that is applied to bee nesting tunnels and results in increased nesting at those sites. Nonetheless, without further improvements in methods to maximize BOB in-orchard reproduction, their use for agricultural pollination will remain economically inviable.
More Flowers Needed
ICP researchers have proposed that the short bloom period of almonds and the lack of floral resources beyond bloom has been a driving factor in limiting the success of BOB reproduction in commercial almonds. Over the course of the 2015 and 2016 almond blooms, in collaboration with Wonderful Orchards, ICP researchers from the University of California, Davis and the USDA-ARS Logan Bee Lab planted three one-acre fields of native wildflowers adjacent to commercially managed orchards in central California.
Flowers were selected based on their known bloom window overlapping with that of almond orchards. Over the course of the almond pollination seasons, the ICP team evaluated the effect that the wildflower plots had on overall BOB reproduction, as well as wild and managed bee visitation to both almond orchards and the flower plots themselves. They also examined the pollen composition of the provisions that female bees provide to their developing offspring to better understand how BOBs use to floral plots to provide resources for their developing larvae.
Published and preliminary results from these studies are encouraging and provide a great deal of support for the planting of alternative resources to benefit nesting BOBs and also foraging honey bees. In 2013 and 2014 studies, when no flower plots were added near orchards, retention of managed BOB populations in some orchards was poor. Without any floral enhancements, female reproduction of bees for use the following year was limited to 30% to 40% of the number of bees initially released.
In 2016, 80% of bees were recovered for the next year, which was likely due to increased female reproduction resulting from an extended foraging window. An analysis of bee visitation to orchards and wildflower plots revealed that floral enhancements provided improved support for wild pollinator communities, and do not detract from insect visitation to almond blossoms by offering competing floral resources.
Finally, female bee provisioning of nests heavily relied upon the availability of wildflower pollen. Even when the wildflower plot was a half-mile from nesting BOBs, females were using wildflower pollen and nectar to make their larval provisions.
These findings may have dramatic implications for the future success on implementing BOB-facilitated pollination in commercial production efforts and cutting growers’ pollination costs.