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RESEARCH PRODUCT

Bees increase oilseed rape yield under real field conditions

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prod 2018-210 EA GESTAD INRA; International audience; Oilseed rape (OSR, Brassica napus L.) is a common crop found in many European agricultural landscapes. It ispollinated by a wide variety of insects, but the reported contribution of pollinators to yield varies widely betweenstudies (from 0 to 50%). Moreover, such a contribution has seldom been estimated at the field scale in realfarming conditions. We analysed OSR yields in response to insect pollination; over four years, at two differentscales: farm fields and individual plants. We used both empirical and experimental approaches along a gradientof pollinator diversity and abundance. The empirical approach was based on farm surveys (151 fields) while theexperimental approach used various pollination exclusion methods (570 plants in 101 fields) to estimate therelative contributions of insect, wind, and self-pollination. The OSR yields were positively correlated to total beeabundance and bee genera diversity, through improved fruiting success and plant seed mass (after adjusting forplant biomass). Hoverfly diversity and abundance, and bumblebee abundance did not have any effect. The mainOSR pollinators in our study were honeybees (Apis mellifera) and wild bees (Lasioglossum spp.). Yields wereincreased, on average, by up to 37.5% (27.7% – 47.5%) at field scale when bee genera diversity increased from asingle genus to more than 10 genera (pan-trap data). Insect pollination contributed about 30% of plant yield.Self-pollination and wind pollination accounted for the remaining 70%, with self-pollination being the majorcontributor. Our study demonstrates that pollinator diversity and abundance, at least at very high levels, have amajor effect on OSR yields. This suggests that establishing a monetary value for pollination services in OSRfarming systems could be used to balance the cost of managing semi-natural habitats or meadows to maintainbees and other pollinators.