Andrena chalybaea

Justification:
Andrena chalybaea is a solitary bee that occurs in central California, from the foothills of the Coast Range east to the Sierra Nevada foothills. Using all known records, the extent of occurrence (EOO) is 46,128 km2 and the area of occurrence (AOO) is 92 km2. The species has not been observed since 2011, and is known from few observations overall. The species is known from 20 localities, which may each be considered individual locations if threats act independently on each locality. It is a narrow dietary specialist, using only pollen from Taraxia ovata (Onagraceae), the distribution of which does not extend much beyond the bee’s known range. Across the range of the species, impacts from habitat degradation, loss, and fragmentation, and climate change and drought have been observed, potentially impacting the distribution and availability of the host plant. Because this species has not been recently observed, is known from limited locations and a small AOO, and faces threats across its range due to habitat degradation and loss, it faces some risk of extinction. Because the number of estimated locations does not meet criteria B2a, it is assessed as Near Threatened for now. NatureServe Specific Text: For Rank Calculator: 1. Element occurrences (using separation distance of 5,000 m): 20 (C) 1. Estimated Number of Element Occurrences Comments: There are limited element occurrences overall, and none since 2011. 2. Population size: Unknown 3. Viability/Ecological integrity (choose one) 1. Number of occurrences with good viability/ecological integrity: Unknown 2. Percent of area occupied (For Species with Known AOO): N/A 4. Environmental Specificity: B. Narrow. Specialist or community with key requirements common. 1. Environmental specificity comments: This species is a dietary specialist, using pollen from the plant species Taraxia ovata, which likely restricts its distribution and phenology. 5. Intrinsic Vulnerability: B. Moderately vulnerable 1. Intrinsic vulnerability comments: Andrena have been reported to have low reproductive output because of the short adult life span, and a low rate of brood cell provisioning (reviewed in Danforth et al. 2019). 6. Trend 1. Short Term Trend: Unknown 2. Comments: Abundance estimates and population trends are not known for this species. 3. Long Term Trend: Unknown 4. Comments: Abundance estimates and population trends are not known for this species. For Biotics Global Element Characterization: 1. Habitat Forest Edge, Shrubland/chaparral, Grassland/Herbaceous Literature References: Brown, Mark J. F., and Robert J. Paxton. 2009. “The Conservation of Bees: A Global Perspective.” Apidologie 40 (3): 410–16. Cane, James H., and Byron G. Love. 2021. “Hygroscopic Larval Provisions of Bees Absorb Soil Water Vapor and Release Liquefied Nutrients.” Apidologie 52 (6): 1002–16. Cane, J. H. 1981. “Dufour’s Gland Secretion in the Cell Linings of Bees (Hymenoptera: Apoidea).” Journal of Chemical Ecology 7 (2): 403–10. Chesshire, Paige R., Erica E. Fischer, Nicolas J. Dowdy, Terry L. Griswold, Alice C. Hughes, Michael C. Orr, John S. Ascher, et al. 2023. “Completeness Analysis for over 3000 United States Bee Species Identifies Persistent Data Gap.” Ecography, February. https://doi.org/10.1111/ecog.06584. Connor, Edward F., John Hafernik, Jacqueline Levy, Vicki Lee Moore, and Jancy K. Rickman. 2002. “Insect Conservation in an Urban Biodiversity Hotspot: The San Francisco Bay Area.” Journal of Insect Conservation 6 (4): 247–59. Danforth, Bryan N., Robert L. Minckley, John L. Neff, and Frances Fawcett. 2019. The Solitary Bees: Biology, Evolution, Conservation. Princeton University Press. Davis, Frank W., Peter A. Stine, and David M. Stoms. 1994. “Distribution and Conservation Status of Coastal Sage Scrub in Southwestern California.” Journal of Vegetation Science: Official Organ of the International Association for Vegetation Science 5 (5): 743–56. Grab, Heather, Michael G. Branstetter, Nolan Amon, Katherine R. Urban-Mead, Mia G. Park, Jason Gibbs, Eleanor J. Blitzer, Katja Poveda, Greg Loeb, and Bryan N. Danforth. 2019. “Agriculturally Dominated Landscapes Reduce Bee Phylogenetic Diversity and Pollination Services.” Science 363 (6424): 282–84. Michener, Charles Duncan. 2007. The Bees of the World. Vol. 1. JHU Press. Packer, Laurence, Amro Zayed, Jennifer C. Grixti, Luisa Ruz, Robin E. Owen, Felipe Vivallo, and Haroldo Toro. 2005. “Conservation Genetics of Potentially Endangered Mutualisms: Reduced Levels of Genetic Variation in Specialist versus Generalist Bees.” Conservation Biology: The Journal of the Society for Conservation Biology 19 (1): 195–202. Potts, Simon G., Jacobus C. Biesmeijer, Claire Kremen, Peter Neumann, Oliver Schweiger, and William E. Kunin. 2010. “Global Pollinator Declines: Trends, Impacts and Drivers.” Trends in Ecology & Evolution 25 (6): 345–53. Raven, Peter H., and David L. Wagner. 2021. “Agricultural Intensification and Climate Change Are Rapidly Decreasing Insect Biodiversity.” Proceedings of the National Academy of Sciences of the United States of America 118 (2). https://doi.org/10.1073/pnas.2002548117. Riordan, Erin C., and Philip W. Rundel. 2013. “The Future of California Sage Scrub in an Era of Increasing Urbanization and Global Climate Change.” Fremontia 41:2–7. Roberts, Stuart, Simon Potts, Koos Biesmeijer, Michael Kuhlmann, William Kunin, and Ralf Ohlemüller. 2011. “Assessing Continental-Scale Risks for Generalist and Specialist Pollinating Bee Species under Climate Change.” BioRisk : Biodiversity & Ecosystem Risk Assessment 6 (December):1–18. Rousseau, Josée S., S. Hollis Woodard, Sarina Jepsen, Brianne Du Clos, Alison Johnston, Bryan N. Danforth, and Amanda D. Rodewald. 2024. “Advancing Bee Conservation in the US: Gaps and Opportunities in Data Collection and Reporting.” Frontiers in Ecology and Evolution 12. https://doi.org/10.3389/fevo.2024.1346795. Thorp, Robbin W. 1969. Systematics and Ecology of Bees of the Subgenus Diandrena (Hymenoptera: Andrenidae). cir.nii.ac.jp. Williams, A. Park, B. I. Cook, and S. E. Smerdon. 2022. “Rapid Intensification of the Emerging Southwestern North American Megadrought in 2020–2021.” Nature Climate Change 12 (3): 232–34. Williams, N. M., Elizabeth E. Crone, T’ai H. Roulston, Robert L. Minckley, Laurence Packer, and Simon G. Potts. 2010. “Ecological and Life-History Traits Predict Bee Species Responses to Environmental Disturbances.” Biological Conservation 143 (10): 2280–91. Wojcik, Victoria A., Lora A. Morandin, Laurie Davies Adams, and Kelly E. Rourke. 2018. “Floral Resource Competition Between Honey Bees and Wild Bees: Is There Clear Evidence and Can We Guide Management and Conservation?” Environmental Entomology 47 (4): 822–33.

Andrena chalybaea is a dietary specialist that uses pollen from the plant Taraxia ovata (formerly Camissonia ovata: Onagraceae). The host plant of this species occurs in grassy, coastal hillsides, from San Luis Obispo north to Shelter Cove. The species has been recorded in grasslands, shrublands, and evergreen forest edges. This species nests underground like all other Andrena (Danforth et al. 2019), with nest entrances surrounded by a tumulus. Females plug the nest entrance with soil when they are away from the nest and when they are done provisioning the nest for the day (Thorp 1969). Nests consist of a short, vertical burrow, with a short lateral shaft and a terminal nest cell (Thorp 1969), which are lined with a waxy Dufour’s gland secretion (Cane 1981) that serves to both isolate the provision from pathogens in the surrounding soil and to regulate water uptake from the soil atmosphere (Cane and Love 2021). Females provision each cell with a ball of pollen moistened with nectar on which they lay a single egg (Michener 2007). This species overwinters as an adult (Thorp 1969). A mark-recapture study of this species found no marked individuals at flower patches just 25 meters from the marking site, indicating short flight distances (Thorp 1969). Records of this species come from February to late April (Chesshire et al. 2023; Thorp 1969). Adults are assumed to emerge annually (Danforth et al. 2019). Parasitism by Nomada spp. has been observed in this species, but does not likely present a risk to the species.

This species occurs in California coastal sage scrub habitat, one of California's most threatened vegetation types, which is globally imperiled (NatureServe 2024). This habitat is highly threatened by modification, fragmentation, and loss due to urban and suburban growth. Nearly half of California’s residents live in the coastal California counties where this habitat occurs, which is less than 10% of the state’s land area (Riordan and Rundel 2013). Less than 20% of this habitat remains (Davis, Stine, and Stoms 1994), and the existing fragments are considered some of most valuable real estate in California. This contributes to considerable development pressure on remaining fragments, and their high real estate value makes their conservation costly. The center of this species range, the California Bay Area, has seen considerable pressure from urbanization in the last several decades. It is estimated that over 40% of developed land is composed of pavement and structures (Connor et al. 2002), which precludes bee nesting. The host plant of this species was described as common in the San Francisco Bay Area, but due to urbanization it has become more restricted in its distribution (Thorp 1969). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena chalybaea is a ground nesting species, and nests may be harmed by certain agricultural practices such as tilling, which can kill bees nesting close to the surface (Williams et al. 2010). This species is a narrow dietary specialist, which has been linked to higher risk of extinction due to reduced host plant availability, especially under climate change scenarios (Roberts et al. 2011) and reduced effective population sizes (Packer et al. 2005). Additionally, Andrena have been reported to have low reproductive output because of the short adult life span, and a low rate of brood cell provisioning (reviewed in Danforth et al. 2019). Other threats to bees generally include habitat loss or modification, climate change, pesticide use, exposure to pathogens from managed bee species, and competition with honey bees (Brown and Paxton 2009; Potts et al. 2010; Wojcik et al. 2018; Grab et al. 2019; Raven and Wagner 2021).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from National Park Service and United States Forest Service land, but this does not confer any specific protections to the species. Further research is needed to determine the overall size of the population and to identify trends and existing threats. Specific conservation needs for this species have not been identified. Due to the importance of supporting wild bee populations for pollination services, general conservation practices are recommended including, restoring, creating, and preserving natural high-quality habitats to include suitable forage and nesting sites; limiting pesticide use on or near suitable habitat, particularly during the adult bee’s flight period; promoting farming and urban practices that increase pollinator-friendly plants in margin space; minimizing exposure of wild bees to diseases transferred from managed bees; and lastly, avoiding honey bee introduction to high-quality native bee habitat.

Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range. More information is needed about the population status, range limits, habitat, and ecology of this species.

(a. any taxonomic concerns about the validity of the species? b. any taxonomic revisions underway that would require a species reassessment.