Andrena chlorogaster

Justification:
Andrena chlorogaster is a dietary generalist bee species that occurs in various habitat types, including human-altered landscapes, in the Western United States. The species has most often been recorded in California, and may be most abundant there. Using all records of the species the extent of occurrence is 1,526,248 km2. Since 2013, the species has been recorded 12 times, in at least six localities. Across the range of the species, impacts from climate change, urbanization and exposure to pesticides have been recorded. These threats may be acting on the species at local levels. More information is needed to determine a population trend for this species, and the degree to which the threats are acting on the species. Because the species is widespread, occurs in several habitat types, and apparently tolerates human-altered landscapes, it is unlikely that the species is threatened with extinction at this time. As such, it is assessed as Least Concern for now.

Andrena chlorogaster is a dietary generalist species, foraging from numerous plant families. It has been observed foraging form species in the following plant families: Fabaceae, Salicaceae, Apiaceae, Rhamnaceae, Ranunculaceae, Ericaceae, and Asteraceae (Ribble 1968). Plant genera thought to be of particular importance to the bee include Lomatium, Salix, and Ceonothus (Ribble 1968). This bee has been observed foraging from the globally imperiled species Arctostaphylos hookeri ssp. hookeri and Lomatium insulare (Buchmann, Adams, and Howell, A, Weiss, M 2010). The bee has been observed in grassland, shrublands, evergreen and deciduous forests, agricultural areas, and urban areas. In one study of bee community phenology in several land use types, the species was almost exclusively recorded in human-altered locations (Leong et al. 2016). 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 February through July, with most observations from March through May (Ribble 1968; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). The presence of Stylops parasites and scutarid mites have been observed on specimens of this species (Ribble 1968).

Specific threats to this species have not been identified. However, it may be subject to increased impacts from drought and pesticide exposure based on the locations 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). This species may be impacted by agricultural intensification, including high exposure to pesticides where it occurs in California’s Central Valley. The Central Valley of California is one of the most intensively farmed regions in the U.S.(Katibah 1984). An estimated 71% of the Central California Valley ecoregion is devoted to agriculture (Soulard and Wilson 2015). This species may be impacted by high exposure to pesticides where it occurs in the Central Valley. This region has some of the nation’s highest pesticide inputs, which can be detected in non-target plant species, sometimes in insect-lethal concentrations, across all land use types (Halsch et al. 2020). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena chlorogaster 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. Observations of this species are known from Bureau of Land Management (BLM), United States Forest Service, United States Fish and Wildlife, and National Park 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. Although there are no taxonomic concerns about the validity of this species, Andrena chlorogaster and be indistinguishable from A. microchlora (Cane, Weber, and Love 2020), which may contribute to some degree of uncertainty with regard to data accuracy.