Attractant spray enhances nesting preference and reduces macroparasite infestation of Osmia cornuta

Mason bees (Osmia. spp) can provide an alternative for crop pollination management in addition to the Western honeybees (Apis mellifera). Targeted evidence-based guidelines can improve cost-effective management of mason bees. Here, I test the effect of an attractant spray developed in the USA for improving the nesting preference for artificial trap nests of mason bees in Belgium. More specifically, this study investigates the effect of the attractant spray on the nesting preference and nesting performance of the European orchard bee (O. cornuta), as well as its effect on the infestation of nest-associated macroparasites. The number of sealed nesting cavities was twice as high in the trap nests that were treated with the attractant spray. Nesting performance expressed as number of brood cells per cavity, successful cocoon formation, adult emergence, proportion of female bees in the offspring and the number of dead larvae was not different between the treated and the untreated nests. Overall infestation of macroparasites, and infestation of drosophilid flies in particular, were both twice as high in untreated nests. This study provides evidence that the attractant spray improves nesting preference and reduces macroparasite infestation in O. cornuta. The use of this attractant can provide growers and stakeholders with an effective management strategy to prevent infestation by macroparasites and promote efficient bee breeding