In this blog post, Yunhui Liu and team discuss their latest research into the importance of honeybees and wild bees for apple pollination, as well as whether the contribution of wild bees is influenced by increasing numbers of honeybees.
Animal pollination is crucial for sustainable crop production and food security. Although there is a growing reliance on pollinators in crop production, global reports indicate a decline in pollinator diversity. Consequently, honeybees (Apis mellifera) are increasingly utilized in commercial crop production. This raises questions regarding the efficiency of introduced honeybees compared to wild bees, and whether their introduction into cropping systems affects the pollination contributions of wild bees.
To address these questions in the context of apple production, Yunhui Liu and colleagues examined wild bees, honeybees, apple quantity (fruit set), and quality (fruit weight, seed number) across 52 Fuji apple orchards in three major apple producing regions in China.
Both honeybees and wild bees contribute to apple quantity and quantity
Both honeybees and wild bees contributed substantially to apple production or quality across all three production areas in China. On average, with bee pollination, fruit set was 61.80%, fresh weight was 229.11g, and seed number was 6.29 across all three production areas. This resulted in a 995.74% increase in fruit set, a 25.64% increase in fresh weight, and a 63.80% increase in seed number, compared to the exclusion treatment.
Maximum pollination contribution was found at intermediate bee density
A hump-shaped relationship between overall bee activity density with pollination contribution to fruitset(PCfruitset), apple weight (PCweight), showed the best pollination contribution at medium level of overall bee activity density (see graph, below).
Similarly, the activity of wild bee and honeybee showed significant effects on PCfruitset, with the highest values of PCfruitset found at medium level of both honeybee activity density and wild bee activity density. Meanwhile, the maximum PCfruitset was achieved with overall ca 16 bees, ca 12 honeybees, but only 8 wild bees, showing that only relatively few wild bees are needed, compared to honeybees.
Interaction between honeybees and wild bees impacts apple pollination contribution
A significant effect of honeybee-wild bee interaction on the PCfruitset and PCweight were found. When wild bee activity or species richness is low, introducing more honeybee individuals related to increasing PCfruitset and PCweight. However, when wild bee activity density or wild bee species richness is high, introducing more honeybees declined PCfruitset and PCweight (see graph, below).
Pollination contributions were always highest when honeybee activity density was at a relatively low level. When the honeybee activity density was low, either high wild bee activity density and species richness was associated with higher pollination contribution than low wild bee activity density or species richness. Particularly, PCfruitset, which is documenting the pollination success, is reaching highest levels only with intermediate honeybee activity density levels. This result indicated that high levels of wild bee density and intermediate levels of honeybee density might be best for maximum fruit set.
Conclusion
Both honeybees and wild bees contribute to apple pollination and production, but wild bees evidenced much higher pollination efficiency than honeybees. Introducing high density of honeybee colonies appeared to enhance competition with wild bees, decreasing their contribution to pollination. Consequently, an effective pollination service management requires a carefully assessment on the number of honeybee colonies before possible introduction of hives for apple production, in particular when wild bee diversity and density are high. Conserving wild bee diversity is of priority to harness pollination services in apple production, given their high diversity and pollination efficiency.
Read the full article, “Honeybees interfere with wild bees in apple pollination in China” in Journal of Applied Ecology.
