Parasite hideouts: Preserving native cavity-nesting Hymenoptera through pollinator hotel management

As many pollinator populations around the world decline due to habitat loss, improving management practices for native pollinators becomes a priority. Pollinators are essential to healthy ecosystems and play irreplaceable roles in the global food system. Pollinator hotels can provide a safe, protected space suited for many different species, and can also be used as educational tools. However, these structures also often contain parasites attracted to the nests within, which can multiply without maintenance. Pollinator hotels are usually filled with nesting cavities in a variety of materials including cardboard, reeds, bamboo, and native plant stems. This study sought to determine whether any materials are more or less prone to parasitic infestation and whether introducing emergence boxes for overwintering bees could offer a solution. We first conducted a family-level biodiversity survey to examine the parasite populations in pollinator hotels. Second, we conducted a controlled study of parasite burden in three material types. Third, we investigated emergence boxes as a tool to facilitate cleaning and maintenance of pollinator hotels with the overall goal of reducing parasitic infestation. We found that cardboard tubes had far higher rates of parasitism than other materials across multiple families of parasites. Elimination of cardboard nest tubes, coupled with regular maintenance, may help protect against parasitism. We also found emergence boxes to be a safe and effective way to house overwintering bees while maintenance is performed; in emergence boxes, very few new parasite holes appeared, and bees and wasps rarely constructed new nests. These results provide guidance for researchers and educators constructing pollinator hotels to select nest materials that safeguard pollinators and implement evidence-based maintenance practices that support pollinators across a wide variety of ecosystems.