Managed Bumblebees Outperform Honeybees in Increasing Peach Fruit Set in China: Different Limiting Processes with Different Pollinators

Peach Prunus persica (L.) Batsch is self-compatible and largely self-fertile, but under greenhouse conditions pollinators must be introduced to achieve good fruit set and quality. Because little work has been done to assess the effectiveness of different pollinators on peach trees under greenhouse conditions, we studied ‘Okubo’ peach in greenhouse tunnels near Beijing between 2012 and 2014. We measured pollen deposition, pollen-tube growth rates, ovary development, and initial fruit set after the flowers were visited by either of two managed pollinators: bumblebees, Bombus patagiatus Nylander, and honeybees, Apis mellifera L. The results show that B. patagiatus is more effective than A. mellifera as a pollinator of peach in greenhouses because of differences in two processes. First, B. patagiatus deposits more pollen grains on peach stigmas than A. mellifera, both during a single visit and during a whole day of open pollination. Second, there are differences in the fertilization performance of the pollen deposited. Half of the flowers visited by B. patagiatus are fertilized 9–11 days after bee visits, while for flowers visited by A. mellifera, half are fertilized 13–15 days after bee visits. Consequently, fruit development is also accelerated by bumblebees, showing that the different pollinators have not only different pollination efficiency, but also influence the subsequent time course of fertilization and fruit set. Flowers visited by B. patagiatus show faster ovary growth and ultimately these flowers produce more fruit. Our work shows that pollinators may influence fruit production beyond the amount of pollen delivered. We show that managed indigenous bumblebees significantly outperform introduced honeybees in increasing peach initial fruit set under greenhouse conditions.

桃（Prunus persica (L.) Batsch）为自交亲和且基本自育的物种，但在温室栽培环境中，必须引入传粉者才能实现良好的坐果效果与果实品质。鉴于目前针对温室环境下不同传粉者对桃树的传粉有效性研究较少，本研究于2012至2014年间在北京周边的温室大棚中以‘大久保’桃（‘Okubo’）为试材开展试验。我们分别测定了两种人工饲养传粉者——拟黄熊蜂（Bombus patagiatus Nylander）与西方蜜蜂（Apis mellifera L.）访花后的花粉沉积量、花粉管生长速率、子房发育情况以及初始坐果率。结果表明，在温室桃树栽培中，拟黄熊蜂的传粉效果优于西方蜜蜂，这一差异源于两个过程：其一，无论是单次访花还是全天开放授粉，拟黄熊蜂在桃花柱头上沉积的花粉粒数量均多于西方蜜蜂；其二，二者沉积花粉的受精性能存在差异。拟黄熊蜂访花的花朵中，有半数在访花后9~11天完成受精，而西方蜜蜂访花的花朵则需13~15天才能达到半数受精。因此，熊蜂访花可加速果实发育，这表明不同传粉者不仅传粉效率存在差异，还会对后续的受精进程与坐果时间进程产生影响。拟黄熊蜂访花的花朵子房生长更快，最终坐果量也更高。本研究证实，传粉者对果实产量的影响不仅限于花粉投递量；我们发现，在温室环境下，本土人工饲养熊蜂在提升桃树初始坐果率方面的效果显著优于引入的西方蜜蜂。