Relationships between wild bee abundance and fruit set of Camellia oleifera Abel

Abstract

Camellia oleifera Abel. is an economically important plant for edible oils. To investigate the importance of wild bee abundance at different canopy and spatial scale for fruit set of Camellia oleifera, we evaluated the relationship of bee abundance with fruit set using yellow pan trap, with additional focus on distance and wild bee abundance counts at a farm in China for 2 years. We found that yellow traps collected 95% more individual bees than the second-best (pink) trap colour. Looking across canopy positions, the number of wild bees (including Colletes gigas, Andrena camellia, Andrena striata, Andrena hunanensis and Andrena chekiangensis) varied significantly in each year. The fruit set also varied significantly based on canopy position. In 2018, there was with an average fruit set of 34.13% in the lower canopy, 54.30% in the middle canopy and 47.41% in the upper canopy. In 2019, fruit set was 29.67% in the lower canopy, 54.15% in the middle canopy and 47.36% in the upper canopy. Comparing inter-annual changes, only the fruit set and number of bees in the low canopy showed significant differences between 2018 and 2019. Fruit set and wild bee abundance were positively correlated in all canopy layers in each year, and there was an interactive effect between canopy and bee abundance on fruit set. Across 205 trees, growth indicators, crown size and tree height, increased significantly from 2018 to 2019, but the fruit set did not increase with the significant increase in the number of flowers. From the spatial perspective, wild bee abundance and fruit set were positively correlated, but fruit set was negatively correlated with distance from a large bee nesting aggregation nearby. Among the variables investigated, bee abundance seems to have the strongest influence on fruit set in C. oleifera.