Dominance of cropland reduces the pollen deposition from bumble bees

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

doi:10.1038/s41598-018-31826-3

Jens Schirmel, James E. Cresswell

Open Access

https://doi.org/10.1038/s41598-018-31826-3

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Abstract

Intensive agricultural landscapes can be hostile for bees due to a lack of floral and nesting resources, and due to management-related stress such as pesticide use and soil tillage. This threatens the pollination services that bees deliver to insect-pollinated crops. We studied the effects of farming intensity (organic vs. conventional, number of insecticide applications) and availability of semi-natural habitats at the field and landscape scale on pollinator visits and pollen delivery to pumpkin in Germany. We found that wild bumble bees were the key pollinators of pumpkin in terms of pollen delivery, despite fivefold higher visitation frequency of honey bees. Critically, we observed that the area of cropland had stronger effects on bees’ pollen deposition than the area of seminatural habitats. Specifically, a 10% increase of the proportion of cropland reduced pollen delivery by 7%. Pumpkin provides a striking example for a key role of wild pollinators in crop pollination even at high numerical dominance of honey bees. In addition, our findings suggest that habitat conversion to agricultural land is a driver of deteriorating pollination. This underlines the importance to maintain sufficient areas of non-crop habitats in agricultural landscapes.

Highlights

Pollination is an important ecosystem service, especially for pollinator-dependent crops such as pumpkin[1]
The abundance and diversity of wild bees are positively influenced by organic farming[22,23] and seminatural habitats at the local and landscape scale[24,25], which usually contain abundant and diverse flower resources i.a. owing to the absence of herbicides[26,27]
Pesticides are frequently found in wild bumble bees, whereby more pesticides were found in bumble bees foraging in agricultural landscapes than in urban landscapes[31]

Summary

Introduction

Pollination is an important ecosystem service, especially for pollinator-dependent crops such as pumpkin[1]. Most existing studies do not distinguish among possible drivers of crop pollination at the landscape scale, namely the availability of seminatural habitats for nesting and alternative floral resources on the one hand, and potential negative drivers such as high proportions of cropland or the intensity of insecticide use in the surrounding landscape on the other[8,10]. We addressed this gap of knowledge by studying pollinator activity and pollen delivery to pumpkin across replicated landscapes. The proportion of cropland and insecticide intensity in the landscape reduce the number of pollinator visits and thereby pollen delivery (landscape effects)

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Conclusion