Wild bees provide important pollination services for crops and wild plants. While land use intensification has resulted in steep declines of wild bee diversity across agricultural landscapes, the creation of semi-natural habitats has been proposed as a countermeasure. However, the relative value of semi-natural and natural habitats in promoting wild bees has rarely been studied, especially for China that harbors the world's largest plantation forest area, characterized by intensively managed, mono-dominant stands of wind-pollinated tree species. We sampled wild bees in apple orchards to assess how their assemblages were influenced by semi-natural habitats in the surrounding landscape and the local flowering ground-cover. Bee abundance declined with increasing isolation from natural shrubland. In contrast, wild bee diversity and abundance were negatively linked to plantation forests. For the abundance of large bees, this effect was partly ameliorated by local flowering ground-cover. Maintaining or restoring wild bee assemblages in agricultural landscapes therefore requires careful evaluations of restoration measures such as forest planting. Availability of local flower resources and nearby natural shrubland appeared particularly important to enhance wild bees and their potential services in apple orchards.

Apple is one of the most widely cultivated fruit crops world‐wide, and apple yield benefits from pollination by insects. The global decline in wild pollinator populations raises concern about the adequacy of pollination services in apple production. Here, we present a global meta‐analysis of pollination in apple. We assembled from the literature a dataset comprising results of 48 studies across five continents on fruit set and seed set in apple with insect pollination, artificial pollination and pollinator exclusion, and analysed the effects of explanatory factors such as variety and continent. Fruit set was on average 41% lower with open pollination than with artificial pollination, while seed set was 20% lower. These pollination deficits varied across continents and cultivars. Pollination deficits for fruit set were greatest in Asia (63%) followed by Europe (30%), whereas pollination deficits for seed set were greatest in Asia (47%) and South America (40%). Important differences in pollination deficit were also identified between cultivars but these differences were confounded with continent effects. Fruit set and seed set were 71% and 62% higher, respectively, when insects had open access to flowers than when they were artificially excluded, while results varied among cultivars. Synthesis and applications. Globally, there are substantial contributions of pollinators to fruit set and seed set in apple, as well as considerable limitations in apple pollination services, particularly in Asia, Europe and South America. Several management strategies could be applied to reduce the pollination deficits in apple production: (1) conserving wild bees and enhancing their abundance and diversity, (2) using managed bees for pollination, (3) using varieties with low pollinator dependency and/or (4) artificial pollination. These strategies should be tailored to the regional situation, considering the potential of landscapes for restoring wild pollinators, the acceptability of cultivated varieties for available pollinators, the acceptance in the market of self‐compatible varieties and the costs of management, such as artificial pollination, pollinator conservation, beekeeping and planting self‐compatible varieties. Conservation of wild pollinators is preferred in regions with sufficient potential for wild pollinators as it contributes to biodiversity conservation and improves pollination in both crops and wild plants.

No abstract

The loss of flower-rich habitats and agricultural intensification have resulted in significant losses of wild bee diversity from agricultural landscapes that is increasingly threatening the pollination of zoochorous agricultural crops and agricultural sustainability. However, the links of different wild bee functional trait groups with habitat types and plant resources in agricultural landscapes remain poorly understood, thus impeding the formulation of effective policies for bee conservation. We therefore analyzed how bees representing different functional groups responded to variations in habitat type, vegetation composition and plant diversity. Natural shrubland sustained the highest diversity in bees overall, in large-sized bees, solitary bees and belowground-nesting bees, while each habitat harbored unique species. In half of the functional bee groups, species were negatively linked to tree coverage and herb coverage, respectively, while plant diversity was positively related to all functional groups except large-sized bees and aboveground-nesting bees. Overall bee abundance was positively related to abundance of plants in the Sympetalae, and negatively related to abundance of plants in the Archichlamydeae. Different bee functional groups showed distinct preferences for different plant communities. In order to conserve the diversity of wild bees across functional groups to optimize associated pollination services, a diverse habitat mosaic, and particularly plant species in Sympetalae need to be promoted in agricultural landscapes. Future studies should aim to enhance our understanding of plant-pollinator associations and specific food requirement of different wild bee species for their effective conservation.

Bees provide key pollination services for a wide range of crops. Accumulating evidence shows the effect of semi-natural habitats at the landscape level and local management practices on bee diversity in fields. However, most of the evidence is derived from studies in North America and Europe. Whether this paradigm is applicable in China, which is characterized by smallholder-dominated agricultural landscapes, has rarely been studied. In this study, we aimed to investigate how bee diversity affected apple production, and how landscape and local variables affected bee diversity and species composition on the Northern China Plain. The results showed that bees significantly increased apple fruit set compared to bagged controls. Wild bee diversity was positively related to apple seed numbers. Higher seed numbers reduced the proportion of deformed apples and thus increased fruit quality. Wild bee abundance was positively correlated with flowering ground cover, and both the abundance and species richness of wild bees were positively affected by the percentage of semi-natural habitats. We conclude that apple quality can benefit from ecological intensification comprising the augmentation of wild bees by semi-natural habitats and flowering ground cover. Future pollination management should therefore reduce the intensification level of management at both the local and landscape scales.