Experimental quantification of insect pollination on sunflower yield, reconciling plant and field scale estimates

International audienceMost crops grown in Europe, including sunflower (Helianthus annulus L.), benefit from insect pollination. However, valuingthis benefit is not straightforward since estimates of the increase in sunflower yield vary from 18% to 100%. Most estimateshave, moreover, been performed at plant scale, a scale that is not relevant for farmers who calculate at the field scale. In thisfour-year study, we quantified the contribution of insect pollination to sunflower yield at field and plant scales in working farmfields distributed along a gradient of pollinator diversity and abundance. Pollinators were found to increase field yield up to 40%(i.e. 0.7 t/ha) and by 31.3% at plant scale; the magnitude of effect on yield being therefore similar at both scales. The pollinatorsincreased the yield by increasing the number of fertilized seeds per plant with no significant effect on the unit mass of the seedsalthough there was a trade-off between number of seeds and unit mass. Among pollinators, honeybees were the main taxonimpacting sunflower yield. Sunflower plant density was a strong determinant of yield, with higher numbers attracting increasednumbers of honeybees. Using pollinator and wind exclusion, we finally quantified the relative contributions of self-pollination(∼40%), insect pollination (∼35%) and wind pollination (∼20%). Our results show, to the best of our knowledge, the firstevidence of the key role of pollinators in sunflower production at field scale in real farming conditions, and underscore the needto maintain suitable conditions for pollinators in agricultural landscapes