Andrena bernardina

Justification:
Andrena bernardina is a solitary bee that occurs in the endangered California coastal sage scrub and warm deserts of southern California, United States. Using all available records, the extent of occurrence is 42,816 km2, and the area of occurrence is 44 km2.The species is known from fewer than 20 observations, and has not been recorded since 1978. The lack of recent records may be attributed to limited recent search effort, as there has only been 58% of the search effort historically required to detect the species within its EOO. Andrena bernardina probably occurs in 10 locations, all of which are likely threatened with habitat fragmentation and habitat modification due to ongoing climate change and drought. Some locations are in proximity to sites slated for lithium development, while other locations have been subject to large-scale wildfire in the last decade. Although six locations occur on Bureau of Land Management or National Forest Service land, these designations offer no specific protections to the species. More surveys are required to determine if this species is extant in its range. Because it is known from a small AOO, only 10 locations, and faces threats from habitat loss and fragmentation, climate change and drought, energy development, and altered fire regime, it is assessed as Vulnerable for now.

Andrena bernardina is a presumed dietary specialist visiting plants from the genus Clarkia (Onagraceae). It has been recorded in the shrublands of southern california, with some records from urban 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). Records of this species come from March through July, with most records from May and June (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats to this species have not been studied. However, climate change and drought, urbanization, and altered fire regime impact the quality of the habitat where this species occurs. Since 2000, the Southwest U.S. has seen the worst drought in 1,200 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 bernadina has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of the plant Clarkia which blooms in response to winter rain, it may be at further risk from winter droughts within its range. This species occurs in California coastal sage scrub habitat, one of California's most threatened vegetation types, which is globally imperiled (NatureServe 2024). This habitat is highly threatened by modification, fragmentation, and loss due to urban and suburban growth. Nearly half of California’s residents live in the coastal California counties where this habitat occurs, which is less than 10% of the state’s land area (Riordan and Rundel 2013). Less than 20% of this habitat remains (Davis, Stine, and Stoms 1994), and the existing fragments are considered some of most valuable real estate in California. This contributes to considerable development pressure on remaining fragments, and their high real estate value makes their conservation costly. Coastal sage scrub has also been modified significantly in the past 100 years due to exotic annual grass invasion, which has been facilitated by increased wildfire frequency (Minnich and Dezzani 1998; Talluto and Suding 2008). These factors also contribute to a feedback where increased grass cover increases fire frequency, leading to grassland conversion. This habitat conversion may limit the availability of host plants used by Andrena bernardina and alter other abiotic factors important for this species. Although six locations of this species are on Bureau of Land Management or United States Forest Service land, this land designation protects them only from the threat of urbanization. Other uses of these land types include energy development and recreational uses that may impact the species. There are several lithium extraction projects slated for within the range of this species, as close as 10 km from an existing location (Parker et al. 2022). Lithium mines, their infrastructure, and roads to access them can directly impact bees through habitat loss. Hydrological impacts from water use at mines can indirectly impact bees by depleting and polluting ground water, which can alter the abundance and composition of flowering plants used by foraging bees. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena bernardina 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 presumed to be 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).

Conservation needs No known conservation actions are in place for this species. 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. Further research is needed to determine the overall size of the population and to identify trends and 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.