Andrena concinnula

Justification:
Andrena concinnula is a pollen specialist, solitary bee species that occurs from southern British Columbia, Canada to Southern California, United States. Using all known records of the species, the extent of occurrence is 871,351 km2. Although there are over 400 records of this species, nearly 75% of those records come from just one locality. It is unclear if the species persists throughout its historic range. The species has not been observed since 2011, despite the fact that there has been nearly 16 times the search effort as was required to detect it prior to 2013. Additionally, there have been no records of the bee in the southern part of its range since 1973. Throughout the range of the species, impacts from drought, urbanization, and exposure to pesticides have been observed. These may be acting on the species at local levels. More information is needed to determine the population trend, threats, and persistence throughout the entire range of the species. As such, it is assessed as Data Deficient for now.

Andrena concinnula is a dietary specialist, visiting plants in the genus Salix (Salicaceae) for pollen. The species has been recorded from shrublands and coniferous forests, and can also be found in agricultural and urban/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 and Love 2021). Females provision each cell with a ball of pollen moistened with nectar on which they lay a single egg (Michener 2007). Adults have been observed in late December (southern California) to late July (Arizona mountains), but most observations come from March and April (Chesshire et al. 2023). Adults are assumed to emerge annually.

There are no specific threats identified for this species. Historic drought and water mismanagement in the western United States has contributed to significant loss of riparian ecosystems, which may reduce the abundance of Salix host plants available as forage for Andrena concinnula. Additionally, certain aspects of this species' biology may make it more vulnerable to some threats. Andrena concinnula 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).

No known conservation actions are in place for this species. Observations of this species are known from United States Forest Service (USFS), National Park Service (NPS), and California State 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.

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.