Importance of Honey Bees as Pollinators

Worldwide Importance of Honey Bees as Pollinators

• The western honeybee ( Apis mellifera) is the most common pollinator of crops globally, but its role in natural habitats is less understood
• A global dataset of 80 plant-pollinator interaction networks and pollinator effectiveness measures from 34 plant species were used to evaluate the importance of A. mellifera in natural habitats.
• A. mellifera visits an average of 13% of flowers across all networks, varying from 0% to 85%.
• In 5% of plant species, A. mellifera is the only documented visitor.
• While A. mellifera visitation is common, 33% of networks and 49% of plant species showed no A. mellifera visits, highlighting reliance on other pollinators.
• A. mellifera visitation is more frequent in warmer, less variable climates and on mainland rather than island sites. Native and introduced ranges did not differ in visitation rates.
• In terms of pollination effectiveness per visit, A. mellifera doesn't differ significantly from other non-A. mellifera pollinators, but it is less effective than the best non-A. mellifera pollinator.
• Understanding A. mellifera's role in natural habitats is important for ecosystem services, conservation efforts, and for potential population shifts/decline.

Methods

• Database for network synthesis: Two approaches were used:
  • A literature search using keywords related to pollination networks, and
  • Downloading existing pollination network data from online databases.
• Data criteria: Networks were from largely unmanaged habitats, included at least five plant species, and a broad range of pollinators. Networks originating from distinct locations (<50 km apart) were considered separate. Data from multiple years of the same study site were pooled.
• Visitation frequency: Mean and median proportion of floral visits by A. mellifera were calculated for all networks and across plant species in 41 networks with A. mellifera records. Plant species with fewer than 10 visits were not excluded.
• Environmental correlates: A zero-inflated multiple beta regression model was built to link A. mellifera visitation to environmental variables. Bioclimatic data (temperature, precipitation), elevation, land type (mainland vs. island) and latitude/longitude were used.
• Pollination effectiveness: Literature searches found 32 studies describing A. mellifera pollination effectiveness. Where detailed data were unavailable, data from figures were extracted. The average effectiveness of A. mellifera visits was compared to the average performance and best performing pollinator.

Results

• Frequency and patterns: A. mellifera, globally, visited 88.89% of networks in its native range, and 61.29% in its introduced range. The average Apis mellifera visitation rate across all networks was 12.64 %.
• Environmental correlates: A. mellifera visits increased with higher overall temperature, isothermality, less temperature variation and less seasonality. Mainland networks had higher visitation compared to island networks. Native/introduced status of A. mellifera didn't significantly influence visitation rates.
• Pollination effectiveness: A. mellifera's single-visit pollination effectiveness was similar to other non-A. mellifera pollinators, but was generally less effective than the most effective non-A. mellifera pollinator. The effectiveness of A. mellifera did not differ between non-agricultural and agricultural plants.