Andrena nigra

Justification:
Andrena nigra is a bee species known from approximately 50 observations from California, United States, and Baja California Norte, Mexico. Additional records of unverified quality come from Arizona, Texas, Oklahoma, Georgia, and New Hampshire. Using all verified records of the species, the extent of occurrence is 125,791 km2. This species has not been observed since 1976, although there has not likely been sufficient recent search effort to detect it. It is unclear if the species persists throughout its range. Within the range of the species, effects from ongoing climate change and severe drought have been observed, as well as impacts from urbanization and exposure to pesticides. These threats may be acting on the species at local levels. More research is needed about the range extent, population trends, habitat and ecology, and threats to this species. As such, it is assessed as Data Deficient for now.

Andrena nigra has been frequently collected from plant genus Phacelia (Boraginaceae), indicating potential dietary specialization, although there are not enough records of this bee to explore its dietary breadth more thoroughly (LaBerge and Bouseman 1977). It has been recorded from the shrublands of the Mojave basin and range, southern California hills, and the central California foothills. The species is also often recorded from urban and suburban areas. This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests from this species have not been described. Nest cells from other members of this genus are located at the ends of the lateral burrows, which are typically lined with a waxy Dufour’s gland secretion (J. H. Cane 1981) that serves to both isolate the provision from pathogens in the surrounding soil and to regulate water uptake from the soil atmosphere (James H. Cane and Love 2021). Females provision each cell with a ball of pollen moistened with nectar before laying a single egg (Michener 2007). Records of this species come from March to June, with most records from April (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats to this species have not been identified. However, since 2000, the Southwest US has seen the worst drought in 1200 years (A. P. Williams, Cook, and Smerdon 2022). Drought can reduce the abundance of flowering plants on a landscape scale, and also reduce pollen and nectar quality (Wilson Rankin, Barney, and Lozano 2020). Drought conditions have been shown to reduce the diversity and abundance of native bees (Hung et al. 2021). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena nigra 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 (N. M. Williams et al. 2010). This species may be oligolectic, 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 U.S. 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 better understand 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.

There may be some confusion between Andrena nigra Provancher 1895, and Andrena nigrae Robertson 1905 in museum specimens. Andrena nigra appears to be a species that occurs primarily in the western United States, and Andrena nigrae appears to occur mostly in the eastern United States.