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

Sonja C Pfister,James E Cresswell,Philipp W Eckerter,Martin H Entling,Jens Schirmel

doi:10.1098/rsos.170102

Sonja C Pfister, James E Cresswell + Show 3 more

Open Access

https://doi.org/10.1098/rsos.170102

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Abstract

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.

Highlights

Pollination is a valuable ecosystem service, especially for crops requiring animal pollination such as pumpkin [1,2]
Our main measure of crop yield is the proportion of fruit set, but we investigated fruit mass because Hokkaido pumpkins are sold for human consumption
We found bumblebees to be the most effective pollinators per flower visit of Hokkaido pumpkins in Germany, and crop yield is most sensitive to declines in bumblebee visits

Summary

Introduction

Pollination is a valuable ecosystem service, especially for crops requiring animal pollination such as pumpkin [1,2]. Pollination services from wild insects are important, even in the presence of honeybees Apis mellifera, because they ensure and enhance pollination through spatial and temporal complementarity, behavioural interactions and higher effectiveness [3,4,5]. Wild bees can be more effective pollinators than honeybees and can increase the fruit set of a wide variety of important cash crops such as almond, spring rape, strawberry, watermelon, cucumber and squash.

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