Towards targeted management of mason bees for tree fruit pollination

Solitary bees are receiving increasing attention as potential crop pollinators. Widespread implementation of pollination management with solitary bees is hampered by a lack of evidence-based guidelines. This study investigated whether different nesting material types – paper straws and wooden grooved boards – are preferred by the European orchard bee (Osmia cornuta). In addition, the influence of nesting material, landscape complexity and timing throughout the nest-construction period of O. cornuta on bee nesting success and infestation of macroparasites was studied. Based on plant−pollinator network data, key plant species were identified to support mason bees. O. cornuta prefers to nest in paper straws compared to wooden grooved boards. Paper straws reduced kleptoparasitic mite infestation. Number of brood cells, successful cocoon development and the sex-ratio decreased throughout the bees’ nest-construction period. The sex-ratio increased with increasing landscape complexity. In addition, the infestation rate of kleptoparasitic mites and kleptoparasitic drosophilid flies increased with time throughout the nest-construction period. O. cornuta forages intensively on tree fruit crops like pear, apple and cherry. Key floral resources before tree fruit flowering are willows and other Prunus species. After fruit tree flowering the possible key floral resources are more diverse. These findings present relevant evidence to aid successful implementation of mason bees for crop pollination via: i)utilizing a nesting material like paper straws or similar (e.g. bamboo) that is preferred by bees and reduces macroparasites, ii) enclosing the nests after tree fruit flowering to reduce macroparasite infestation, and, iii) providing diverse floral resources to support bee nesting success.