Andrena candidiformis

Justification:
Andrena candidiformis is a widespread and common species in the western United States found in several states and ecosystem types. Using all known observations of this species, its extent of occurrence is 1,497,525 km2. However, the species has not been recorded since 2006, despite over 11 times as much search effort within its range as was required to detect it prior to 2013. Within the range of the species, increased severe wildfire, urbanization and agricultural development have been observed, so it is possible that localized threats are acting on this species, but currently, there are no clear threats to the species at a range-wide scale. Although A. candidiformis may have a restricted diet compared to true generalists, its primary forage plants are abundant, widespread, and occur in many different habitats. However, further research is needed to establish full details of population size, trends, and threats to the species. For now, this species is assessed as Least Concern.

Andrena candidiformis appears to be a pollen generalist that visits plants from several plant families including Rhamnaceae, Apiaceae, Salicaceae, and Rosaceae. Most floral records associated with this species come from the genera Ceanothus, Lomatium, and Salix, indicating a potential preference (Ribble 1967). Although the species can be found in the U.S. southwest, A. candidiformis is not associated with low desert habitats. All records from Arizona and Nevada are all from high elevations (Ribble 1967). Records from California and Oregon come from mountain foothills and montane forests. This species likely nests underground like all other Andrena (Danforth et al. 2019). 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). Most records of this species come from April, May, and June, although there are some records from as early as March, and as late as July (Ribble 1967). Adults are assumed to emerge annually (Danforth et al. 2019).

There are no specific threats identified for this species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena candidiformis 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 may have a restricted dietary preference, 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).

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 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?):