The identity of crop pollinators helps target conservation for improved ecosystem services

Abstract

Insect pollinated mass flowering crops are becoming more widespread and there is a need to understand which insects are primarily responsible for the pollination of these crops so conservation measures can be appropriately targeted in the face of pollinator declines. This study used field surveys in conjunction with cage manipulations to identify the relative contributions of different pollinator taxa to the pollination of two widespread flowering crops, field beans and oilseed rape. Flower visiting pollinator communities observed in the field were distinct for each crop; while field beans were visited primarily by a few bumblebee species, multiple pollinator taxa visited oilseed, and the composition of this pollinator community was highly variable spatially and temporally. Neither pollinator community, however, appears to be meeting the demands of crops in our study regions. Cage manipulations showed that multiple taxa can effectively pollinate both oilseed and field beans, but bumblebees are particularly effective bean pollinators. Combining field observations and cage manipulations demonstrated that the pollination demands of these two mass flowering crops are highly contrasting, one would benefit from management to increase the abundance of some key taxa, whilst for the other, boosting overall pollinator abundance and diversity would be more appropriate. Our findings highlight the need for crop specific mitigation strategies that are targeted at conserving specific pollinator taxa (or group of taxa) that are both active and capable of crop pollination in order to reduce pollination deficits and meet the demands of future crop production.

Keywords: Bumblebees; Crop pollination; Crop pollinators; Ecosystem service; Field beans; Oilseed rape; Pollinator conservation.

Fig. 1

Visits/flower/minute shown by some potentially important pollinator taxa legitimately visiting field beans across eight field sites in Berkshire, UK. Mean ± S.E.M.

Fig. 2

Visits/flower/minute shown by some potentially important pollinator taxa visiting oilseed rape across eight field sites in Yorkshire, UK. Mean ± S.E.M.

Fig. 3

Pods per node on field beans following visitation by four different pollinators at three visitation rates per flower (1 = [], 2 = [], 4 = [] visits). Pods per node following pollinator exclusion and hand pollination also shown, Mean ± S.E.M. Treatments with different letters are significantly different according to a linear mixed effects model.

Fig. 4

Seeds per pod of oilseed rape following pollination by four different pollinators at two visitation rates per flower ([] = 1, [] = 3 visits). Seed numbers following pollinator exclusion and hand pollination also shown, Mean ± S.E.M. Treatments with different letters are significantly different according to a linear mixed effects model.