The utility and use of solitary bees for pollination in greenhouses and other covered growing systems: A review.

Globally, the area of protected cropping has grown exponentially in the past 25 years. Concomitantly, the number of greenhouse crop species has increased, and a substantial proportion of these rely on, or benefit from, bee pollination. Both in crops grown outside and under cover, diversity in pollinating species could create resilience in this important service. Here we review, for the first time, the utility and use of solitary bee species for crop pollination in protected cropping environments. An increasing number of bee species, including solitary bees, are managed for pollination of crops grown outside, and our review shows that there is no shortage of solitary species able to pollinate crops grown under protective covers. Despite this, only four solitary species are used on a small commercial scale, and only in orchard crops, while pollination in greenhouses worldwide is delivered by a few, often introduced, bumble bee species. We argue that there are two impediments to the use of solitary bees for pollination in protective cropping environments: (a) Bumble bees satisfy most current greenhouse requirements, and (b) There are intrinsic difficulties in relation to husbandry and reliable large-scale supply of solitary bees, in particular when they are required year-round. We explore the possibility to overcome the second impediment by selecting species with suitable life-history traits or by deploying multiple species.