Andrena costillensis

Justification:
Andrena costillensis is a pollen specialist bee that occurs in the shrublands and forests of the Rocky Mountains in the United States and Canada. Using all known records for this species, the extent of occurrence is 2,206,282 km2. Recent records for this species are fairly well distributed throughout the historic range, with the exception of the northwest most part of the range encompassing Alaska. The persistence of this species in this part of its historic range is not well understood. Although it is a pollen specialist, which can be linked to higher extinction risk, it specializes on hosts in the species-rich plant family Asteraceae, so host plants are likely abundant, widespread, and bloom throughout the adult flight period of this species. Within the range of the species, increased impacts from climate change, 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 and occurs in many different ecoregions, it is unlikely that it is threatened with extinction at this time. Therefore, it is assessed as Least Concern.

Andrena costillensis is a pollen specialist bee that uses pollen from the plant family Asteraceae. It has been recorded foraging from the genera Agoseris, Erigeron, Heterotheca, Heliomeris, Chrysothamnus, and Grindelia. It has been recorded from the foothill shrublands to the sub-alpine forests of the Rocky Mountain region. This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests of 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 July and August (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). Habitat:

Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena costillensis 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 oligolectic, 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). This species has had its conservation status evaluated using NatureServe criteria at the U.S. state and Canadian province level in some areas where it occurs. It has been evaluated as Vulnerable in British Columbia, Canada, and Critically Imperiled in Alaska, U.S.

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), United States Fish and Wildlife land, and National Park Service (NPS) 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.

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.