Andrena chlorosoma

Justification:
Andrena chlorosoma is a solitary bee species that occurs in California, United States, from the San Francisco Bay Area south to the Los Angeles Area, and east to the western Sierra Nevada mountains. Using all observations, the extent of occurrence is 99,629 km2. This species has not been observed since 2012, therefore the degree to which this species persists throughout its entire range is not well understood. Although this species is a dietary specialist, using pollen from just a subset of Asteraceae species, it has also been recorded foraging from introduced species. It occurs in shrublands, evergreen forests, and urban areas. The most recent observations of this species come from urban/suburban edges. This, combined with the use of introduced plant species for pollen, suggests that the species may tolerate some habitat disturbance. Across the range of the species, threats from climate change, drought, and exposure to pesticides have been observed. These threats may be acting on the species at local levels. More information is needed to assess the range limits, population trend, and the degree to which threats are acting on the species. Because the species is relatively widespread, occurs in several habitat types, and may tolerate some habitat disturbance, it is assessed as Least Concern for now.

Food habits comment: Andrena chlorosoma is a dietary specialist, and collects pollen from the plant family Asteraceae, specifically ligulate flowered Asteraceae members, including the genera Agoseris, Sonchus, Hypochaeris, Taraxacum, Layia, and Lasthenia, among others (Thorp 1969). The species has been recorded foraging for pollen mainly from mid- to late-morning (Thorp 1969). The species was originally hypothesized to specialize on Ranunculus (Ranunculaceae), but analysis of pollen on scopal loads suggests that this species is in fact an Asteraceae specialist (Thorp 1969). Nectaring on Ranunculus is common (Thorp 1969). Habitat comment: This species has been recorded in shrublands, evergreen forest, and urban areas. Reproduction comment: 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). Phenology comment: Records of this species come from March to May (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Threat comments: Specific threats to this species have not been identified. However, this species may be impacted by severe drought in some parts of its range. 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). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena chlorosoma 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 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. Protected/Managed area comment: Observations of this species are known from U.S. Forest Service and National Park Service land but this does not confer any specific protections to the species. Management comment: 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.

Research need comment: More information is needed about the population status, population trend, existing threats, range limits, habitat, and ecology of this species. Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range.

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