Andrena principalis

Justification:
Andrena principalis is a pollen specialist solitary bee species that visits plants from the genus Arctostaphylos (Ericaceae) for pollen. Using all verified records of the species, the extent of occurrence is 1,991,146 km2, and occurs in California and Oregon, United States. Across the range of the species, impacts from climate change, wildfire, and urbanization may be acting on the species at local scales. However, recent records from across the range of the species suggest that the species may persist through much of its historic range. More information is needed to describe the habitat and ecology of the species, and to assess population trends and impact of threats. For now it is assessed as Least Concern.

Andrena principalis is a dietary specialist species that visits plants from the genus Arctostaphylos (Ericaceae) for pollen (LaBerge, 1985). The species can be found in forests and shrublands of the California Coast Range, and Sierra Nevada foothills. It can also be found in suburban 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 & 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 November to April, with most records from December and January (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 principalis 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 & Paxton, 2009; Grab et al., 2019; Potts et al., 2010; Raven & Wagner, 2021; Wojcik et al., 2018).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from U.S. Forest Service and U.S. 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 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.