Solitary Bees as Vital Bioindicators: A Comprehensive Review of the Diversity, Decline, and Conservation Imperatives of the Halictidae Family

Abstract

Pollination, a keystone ecological process sustaining most flowering plant communities, is indispensable to human survival, with over 500 cultivated plant species relying on insect pollinators. Solitary bees (Hymenoptera: Apoidea) are critical contributors to this service, requiring specialized foraging, nesting, and habitat resources. Plant diversity strongly correlates with pollinator community composition, underscoring the ecological interdependence of these groups. Within solitary bees, the family Halictidae (~4500 species) plays a disproportionately significant role in global pollination networks. Halictids exhibit remarkable diversity in social organization—ranging from solitary to communal, semi-social, and primitively eusocial behaviors—shaped by floral resource availability, geographic distribution, and climatic factors. The subfamily Halictinae represents the group's greatest diversity, with the tribe Halictini comprising 53.3% of described species. Key pollinator genera such as Lasioglossum (e.g., Lasioglossum marginatum, Lasioglossum leucozonium) dominate temperate ecosystems. However, population declines in solitary bees have severely disrupted pollination services across wild and cultivated plant systems, exacerbating global concerns over insect biodiversity loss and biomass reduction. These declines threaten foundational ecosystem services, necessitating urgent research to refine species diversity estimates, identify habitat conservation priorities, and implement evidence-based protective policies. This review highlights the need for standardized methodologies to accurately assess global bee diversity and proposes targeted strategies to mitigate conservation challenges for Halictidae and other solitary bee taxa.