Hummingbirds, honeybees, and wild insect pollinators affect yield and berry quality of blueberries depending on cultivar and farm's spatial context

Abstract

The contribution of wild pollination service to global agriculture is increasingly recognized. Still, biotic pollination demand is mainly covered by managed species, whereas implementing ecological intensification practices to promote wild pollination service remain less common. In this study, we evaluated (i) the effect of wild and managed pollinators and the richness of pollinator functional groups (RPFG) on production quality (i.e., fruit size) and quantity (i.e., crop yield), of two southern highbush blueberry (Vaccinium corymbosum) cultivars, and (ii) how wild pollinator service and crop production correlate with farm’s land cover. We found that pollination service supply and the spatial context interact with the blueberry cultivar to determine yield and fruit size. The abundance of big-sized wild bees and hummingbirds positively affected fruit size and crop yield, but the relationship's significance was cultivar-dependent. In contrast, the increase in honeybees visitation rate was detrimental to the average fruit size of blueberries, but the effect was not generalizable between cultivars. The amount of forested area affected positively wild pollinator abundance and RPFG only in one cultivar, whereas grassland and hedgerow had adverse effects for pollinators in the other. Consistently, the relation between blueberry fruit size and the farm’s land cover was subordinate to the cultivar. That is, despite all significant relations had the same sign between cultivars, their coefficients were statistically different. Our results support the idea that wild pollinators contribute to producing higher yields and larger berries in blueberry crops. Moreover, we found that the retention of natural forest at a 200 m radius within the farm may increase pollination service supply. However, the significance of every effect was contingent on the blueberry cultivar. This cultivar-dependent response points out that a robust assessment of pollinator benefits not only should include multiple production metrics, but also must incorporate within-crop variation, particularly in systems where growers use a mosaic of cultivars with different pollination requirements.