Landscape complexity benefits bumble bee visitation in faba bean (Vicia faba minor L.) but crop productivity is not pollinator-dependent

Ola Lundin,Chloé A Raderschall

doi:10.1016/j.agee.2021.107417

Ola Lundin, Chloé A Raderschall

Open Access

https://doi.org/10.1016/j.agee.2021.107417

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Abstract

Faba bean (Vicia faba minor L.) is partially dependent on insects for pollination, but the degree of pollinator-dependency and whether crop productivity is limited by insufficient insect pollination remain unknown. We monitored insect pollinators and their foraging behaviors (i. e., legitimate flower visitation, nectar robbing and extra-floral nectary visitation) in a total of 20 faba bean fields of a single cultivar (Tiffany) 2018–2019. Focal fields were situated along a gradient of landscape complexity. In each field, a pollination experiment was established, where plants were either bagged to exclude pollination by insects or remained open for pollinator visits. In addition, all flowers on half of the bagged and open-pollinated plants were pollinated by hand to measure the degree of pollen limitation. We found that bumble bee abundance was higher, and legitimate flower visitor abundance tended to be higher, in complex landscapes with more semi-natural habitat, indicating that the faba bean pollination potential is higher in complex landscapes. The pollination experiment showed that the number of beans per pod was lower in bagged plants compared with other treatments in one of the years, but the lower number of beans per pod was compensated for by a higher individual bean weight, such that there was no pollinator-dependency or effect of hand pollination on total bean mass per plant. We conclude that to be able to characterize the value of insect pollination services in faba bean we need an improved understanding of how pollinator-dependency varies across modern cultivars, and how environmental conditions can increase or, as in our case, cancel this pollinator-dependency.

Highlights

Animal pollination, mainly performed by bees, benefits over 75% of the world’s most common crops and is a key ecosystem service sup porting the nutritional needs and wellbeing of people globally (Klein et al, 2007; IPBES, 2016; Dainese et al, 2019)
Legitimate flower visitor and nectar robber abundance tended to be positively related to proportion of semi-natural habitat (SNH) (Fig. 3c, d, Table 1), whereas extra-floral nectaries (EFN) visitor abundance was not related to proportion of SNH, field size, crop bloom or year (Tables 1 and 2)
The proportion of legitimate flower visitors, nectar robbers of EFN visitors was not related to proportion of SNH, field size, crop bloom or year (Tables 1 and 2)

Summary

Introduction

Mainly performed by bees, benefits over 75% of the world’s most common crops and is a key ecosystem service sup porting the nutritional needs and wellbeing of people globally (Klein et al, 2007; IPBES, 2016; Dainese et al, 2019). Long-tongued species of bumble bees are declining in Europe (Dupont et al, 2011; Bommarco et al, 2012), probably largely as a result of loss of SNH rich in Fabaceae plants, which long-tongued bumble bee species are specialized in gathering pollen from (Goulson et al, 2005). These trends suggest that pollen limitation, due to insufficient insect pollination, is increasingly limiting crop yields, especially for crops benefitting from visits by long-tongued bumble bees, but this is poorly documented. An important caveat of such a correlative approach is that alternative hidden drivers of crop production that correlate with bee abundance, such as pest control due to shared environmental drivers (Lundin et al, in press), cannot be excluded from being responsible for the relationships observed (Petersen and Nault, 2014)

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