Andrena coracina

Justification:
Andrena coracina is a solitary bee species known from just 15 observations that occurs in the Mojave Basin of southern California and southern Nevada. Using all observations of the species, the extent of occurrence (EOO) is 18,823 km2. The species has not been recorded since 1998, although this is likely a reflection of limited search effort where it occurs. It is unclear if it persists throughout its known range. This species likely occurs in six locations, with two of them possibly impacted by mining expansion, one in Nevada and one in California. The Nevada location in proximity to the mine has also been altered by urbanization. All locations occur in an area that has been seriously impacted by a decades long drought, which likely limits the quality and quantity of forage required by this species. More information is needed to determine if this species is still extant throughout its known range, to describe the life history of the species, and to determine the degree to which threats like climate change and habitat degradation act on the species. Because the species is known from a small EOO, occurs in limited locations, and its habitat quality is projected to decline due to impacts from climate change and habitat degradation, it is assessed as Vulnerable.

There is limited habitat and ecology information available for this species. There are no associated floral records. Records come from the deserts and shrublands of the Mojave Basin. One recorded locality for this species is the immediate edge of urban Las Vegas. 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 (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). Records of this species come from March through May (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats to this species have not been studied. However, the range of this species is threatened by climate change and drought, as well as increased urbanization. Since 2000, the Southwest U.S. has seen the worst drought in 1200 years (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 (Minckley, Roulston, and Williams 2013; Hung et al. 2021). Two locations of this species are located in Clark County, which had the second largest county population growth in the United States in 2017 (Brean 2018). One of the most recent recorded localities (1998) is at the edge of a gravel quarry and rock dumping location in Las Vegas, NV. Although this facility was located there when the species was detected there, much of the surrounding area was undeveloped. It has since been built up with residential housing. Another recorded locality of the species, near Kramer Hills, California, appears to be at the edge of another small mine facility. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena coracina 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). 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. One locality of this species comes from the US Fish and Wildlife managed Desert National Wildlife Range, 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. Conservation efforts should focus on investigation of dietary breadth and nesting substrate required for this species, and protecting host plant populations and suitable nest sides. Mining and quarrying should be limited in areas where this species occurs. 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.