Andrena angustella

Justification:
Andrena angustella is a solitary bee that occurs on the west coast of the United States, with most records from the central and northern California coast. It ranges from Southern California, United States north to southern British Columbia, Canada. Using all known observations of the species, the extent of occurrence is 672,959 km2, but the species has not been observed anywhere in its range since 2005, with apparently four times as much search effort in the last decade as was required to detect it historically. It appears to be a dietary generalist, and has been recorded in grasslands, forests, shrublands, agricultural, and rural areas. Across the range of the species, threats from changed fire regime and increased fire severity, pesticide exposure, and urbanization have been observed. These may be acting on the species at local levels. Although this species is relatively widespread and occurs in many habitats, absence of recent records contribute to uncertainty about its extinction risk. As such it is assessed as Data Deficient for now.

Andrena angustella appears to be a dietary generalist, although there are limited associated floral records for this species (LaBerge 1985). The species has been recorded foraging from several plant families, including Asteraceae, Rosaceae, Fabaceae, Ranunculaceae, and others. It has been recorded from grassland, shrubland, evergreen forest, agricultural and urban 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 (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 June, with most records from April and May (LaBerge 1985; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena angustella 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, 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.