Andrena astragali

Justification:
Andrena astragali is a widespread and locally common bee across most of the western United States The extent of occurrence for this species is 2,516,223 km2, and it is regularly encountered where its host plants grow. The species is a narrow pollen specialist that visits only members of the plant genus Toxicoscordion (Melanthiaceae) for pollen. Although its dietary breadth is narrow, its host plant is avoided by other herbivores due to its toxic foliage. Within the range of the species, climate change impacts, increased urbanization and agricultural development have been observed, so it is possible that localized threats are acting on this species. However, because the species is widespread, locally common, and occurs in different ecoregions, it is unlikely that it is threatened with extinction at this time. Therefore, it is assessed as Least Concern.

Andrena astragali is a very narrow pollen specialist, collecting pollen only from plants in the genus Toxicoscordion (Melanthiaceae), including Toxicoscordion fremontii, Toxicoscordion nuttallii, Toxicoscordion paniculatum, and Toxicoscordion venenosum, and possibly other species in the genus (Tepedino 1981; Irwin et al. 2014; Cane 2018). In general, this bee is almost always present in sub-alpine to rolling chaparral that has long term populations of its host plant (H. Ikerd, pers. com. with S. Killingsworth April 2023). This species nests underground according to field notes of Dr. Ned Bohart (USDA, Logan Utah), but nests for this species were never 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 before laying a single egg (Michener 2007). The adult flight period appears to span only a few weeks at any local site, but records for this bee are from April to July, with the phenology associated with Toxicoscordion flowering that progresses up a 900 m elevation range (Cane 2018; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). Habitat

There are no specific threats identified for this species, although it does appear to be disproportionately abundant in bee sampling efforts when bowl or pan traps are used in proximity to its host plant. Pan or bowl traps should not be deployed in proximity to blooming Toxicoscordion, as this has resulted in hundreds of dispatched A. astragali in just a few collection events (H. Ikerd, personal communication with S. Killingsworth April 2023). Certain aspects of this species' biology may make it more vulnerable to some threats. This species is a very narrow pollen 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). However, the host plant of Andrena astragali is not eaten by livestock as it is both irritating and toxic, and may even be benefitted when overgrazing removes its competition (J. Cane, pers. com. with S. Killingsworth April 2023). 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).

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 (USFS), and National Park 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.

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