Worldwide importance of insect pollination in apple orchards: A review

Apple (Malus domestica) is one of the most important fruit crops globally. Apple trees depend greatly on insect pollination to achieve high yields and obtain fruits of acceptable marketable quality. Since insects, such as bees and hoverflies, are most important pollinators in apple orchards, a comprehensive understanding of their occurrence and activity is vital to ensure pollination services in this agroecosystem. Here, we review and synthesize the published research on the contribution of insects to apple pollination. In our review, we focused on the following five questions: i) Are there gaps in data availability across geographical regions and research topics? ii) What is the importance of insect pollination at determining yield and fruit quality in apple orchards? iii) What is the relative contribution of wild insects to apple pollination compared to honeybees? iv) What is the influence of landscape context (matrix) on regulating apple pollination? and v) How does agricultural management affect apple pollination?. Results showed that the information is limited for certain large apple producing countries, like China or Brazil. This finding stresses the need for further research in less studied regions. There were also gaps across research topics, highlighting the need for more experimental and empirical studies, particularly on the effect of local management practices on apple pollination. Substantial evidence from qualitative analyses supports the fact that insect pollination is essential for ensuring both yields and fruit quality in apple orchards across different regions. Besides, a significant proportion of studies showed that wild pollinators are abundant in apple orchards and they are frequently more effective pollinators than honeybees. Current available findings suggest a critical role of diverse semi-natural habitats surrounding apple orchards to sustain healthy pollinator communities, while the effect of local management was less consistent.