Sensitivity of commercial pumpkin yield to potential decline among different groups of pollinating bees

The yield of animal-pollinated crops is threatened by bee declines, but its precise sensitivity is poorly known. We therefore determined the yield dependence of Hokkaido pumpkin in Germany on insect pollination by quantifying: (i) the relationship between pollen receipt and fruit set and (ii) the cumulative pollen deposition of each pollinator group. We found that approximately 2500 pollen grains per flower were needed to maximize fruit set. At the measured rates of flower visitation, we estimated that bumblebees (21 visits/flower lifetime, 864 grains/visit) or honeybees (123 visits, 260 grains) could individually achieve maximum crop yield, whereas halictid bees are ineffective (11 visits, 16 grains). The pollinator fauna was capable of delivering 20 times the necessary amount of pollen. We therefore estimate that pumpkin yield was not pollination-limited in our study region and that it is currently fairly resilient to single declines of honeybees or wild bumblebees.

依赖动物传粉的作物产量正面临蜂类种群衰减的威胁，但其精确的敏感性仍鲜为人知。为此，我们通过量化两项指标，明确了德国境内北海道南瓜的产量对昆虫传粉的依赖程度：(i) 花粉接收量与坐果率之间的关联；(ii) 各类传粉者的累积花粉沉积量。
研究发现，每朵花需接收约2500粒花粉方可实现坐果率最大化。基于实测的访花速率，我们估算得出：熊蜂(Bumblebees)（每朵花生命周期内21次访花，单次访花可携带864粒花粉）或蜜蜂(Honeybees)（单花生命周期内123次访花，单次访花可携带260粒花粉）均可单独实现作物产量最大化，而隧蜂科蜂类(Halictid bees)则无此增效作用（单花生命周期内11次访花，单次访花仅16粒花粉）。
传粉者群落所能提供的花粉总量可达所需阈值的20倍。因此我们估算，在本研究区域内，南瓜产量并未受到传粉限制，且当前即便仅出现蜜蜂或野生熊蜂单一种群的衰减，该作物仍具备较强的抗风险韧性。