Andrena flandersi

Justification:
Andrena flandersi is a solitary bee that occurs in the Mojave Desert of southern California United States. It is known from fewer than 40 observations. Using all records of the species, the extent of occurrence is 39,525 km2. It has not been observed since 1977, so it is unclear if the species is extant throughout its entire known range. The species is a dietary specialist that uses pollen from the plant genus Cammisonia (Onagraceae) to provision nests. It occurs in desert shrublands and grasslands. Across the range of the species, impacts from climate change, specifically a decades long drought has been observed. This drought likely influences the quality and the quantity of the host plants available for this species. Andrena flandersi is also likely threatened by habitat loss and degradation and exposure to pesticides. This species may occur in just one location if climate change impacts the entire range of the species equally. Because the species has not been observed in nearly 50 years, and is known from a relatively small range impacted by climate change, it faces some extinction risk. However it does not meet the threshold for imperiled based on its extent of occurrence under Criterion B. Therefore it is assessed as Near Threatened at this time.

Food habits comment: Andrena flandersi is presumed to be a dietary specialist, and collects pollen from plants in the genus Camissonia (Onagraceae) (LaBerge and Thorp 2005). Habitat comment: This species has been recorded in the grassland and shrubland of the Mojave Desert, between 84 and 1757 m. Reproduction comment: 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). Phenology comment: Records of this species come from March through June (Chesshire et al. 2023; LaBerge and Thorp 2005). Adults are assumed to emerge annually (Danforth et al. 2019).

Threat comments: Specific threats to this species have not been directly investigated. This species may be impacted by climate change and drought. Since 2000, the Southwest U.S. has seen the worst drought in 1200 years (Williams, Cook, and Smerdon 2022). Drought can reduce the abundance of flowering plants on a landscape scale, and also reduce pollen and nectar quality (Wilson Rankin, Barney, and Lozano 2020). Drought conditions have been shown to reduce the diversity and abundance of native bees (Minckley, Roulston, and Williams 2013; Hung et al. 2021). Because Andrena flandersi has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of the plant Camissonia which blooms in response to winter rain, it may be at further risk from winter droughts within its range. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena flandersi 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 and Paxton 2009; Potts et al. 2010; Wojcik et al. 2018; Grab et al. 2019; Raven and Wagner 2021). Threats Threats:

Conservation needs No known conservation actions are in place for this species. Protected/Managed area comment: Observations of this species are known from Bureau of Land Management (BLM) and United States Forest Service land, but this does not confer any specific protections to the species. Management comment: 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.

Research need comment: More information is needed about the population status, population trend, existing threats, range limits, habitat, and ecology of this species. Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range.

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