Abstract
Concerns over the availability of honeybees (Apis mellifera L.) to meet pollination demands have elicited interest in alternative pollinators to mitigate pressures on the commercial beekeeping industry. The blue orchard bee, Osmia lignaria (Say), is a commercially available native bee that can be employed as a copollinator with, or alternative pollinator to, honeybees in orchards. To date, their successful implementation in agriculture has been limited by poor recovery of bee progeny for use during the next spring. This lack of reproductive success may be tied to an inadequate diversity and abundance of alternative floral resources during the foraging period. Managed, supplementary wildflower plantings may promote O. lignaria reproduction in California almond orchards. Three wildflower plantings were installed and maintained along orchard edges to supplement bee forage. Plantings were seeded with native wildflower species that overlapped with and extended beyond almond bloom. We measured bee visitation to planted wildflowers, bee reproduction, and progeny outcomes across orchard blocks at variable distances from wildflower plantings during 2015 and 2016. Pollen provision composition was also determined to confirm O. lignaria wildflower pollen use. Osmia lignaria were frequently observed visiting wildflower plantings during, and after, almond bloom. Most O. lignaria nesting occurred at orchard edges. The greatest recovery of progeny occurred along the orchard edges having the closest proximity (80 m) to managed wildflower plantings versus edges farther away. After almond bloom, O. lignaria nesting closest to the wildflower plantings collected 72% of their pollen from Phacelia spp., which supplied 96% of the managed floral area. Phacelia spp. pollen collection declined with distance from the plantings, but still reached 17% 800 m into the orchard. This study highlights the importance of landscape context and proximity to supplementary floral resources in promoting the propagation of solitary bees as alternative managed pollinators in commercial agriculture.
Highlights
The California almond (Prunus dulcis Mill.) industry relies heavily on the availability of honeybees (Apis mellifera L.; Hymenoptera: Apidae) to meet the pollination demands of their orchards (Traynor, 2017)
From the 2016 analysis of O. lignaria pollen provisions, we confirmed that nesting females collected pollen from the wildflower plantings from up to 800 m away
Most nest completion occurred at orchard edges, and significantly, more cells were recovered from A1 over A2, which is likely a consequence of closer proximity to wildflower plantings
Summary
The California almond (Prunus dulcis Mill.) industry relies heavily on the availability of honeybees (Apis mellifera L.; Hymenoptera: Apidae) to meet the pollination demands of their orchards (Traynor, 2017) These demands have grown in recent years as the amount of almond-bearing acreage exceeds 470,000 ha (CDFA, 2019), requiring over two million honeybee hives annually during bloom (Goodrich & Goodhue, 2016), and accounting for 73% of the U.S honeybee population (as of January 2017; Goodrich, 2018). Almond blossoms are only available to foraging bees for 2–3 weeks of the year, which does not fully accommodate the 4–6-week life span of foraging O. lignaria This limits the foraging period of O. lignaria in commercial orchards, where intense chemical control of weeds and other vegetation prevents pollinator access to supplementary floral resources that may extend their reproductive season and improve their overall nutrition. Visitation to wildflower plantings, rates of bee reproduction, progeny outcomes, and pollen composition of representative provision masses were compared across six discrete distances (or “zones”) from the maintained wildflower plantings to verify the use of alternative floral resources
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