Andrena blaisdelli

Justification:
Andrena blaisdelli is a solitary bee species that occurs in southern California, United States, and northern Baja California Norte, Mexico. Using all known observations of the species, the extent of occurrence is 49,870 km2, however, the species has only been observed in one locality since 1970, where it was recorded in 2015 and 2016. The species is a dietary specialist, collecting pollen from plants in the genus Camissonia, and has been recorded in shrublands and grasslands. Much of the range of Andrena blaisdelli has seen extremely high development pressure in the last several decades, and much of California coastal sage scrub habitat where it has been recorded has been lost, degraded or highly fragmented. These threats may be acting on the species across its range. SENTENCE ABOUT SEARCH EFFORT, RANK

This species is a dietary specialist that collects pollen from the plant genus Camissonia (Onagraceae) to feed its larvae, mostly Camissonia campestris and Camissonia bistorta (LaBerge and Thorp 2005). It has been recorded in grasslands, shrublands, and 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 August, with most records from March through May (LaBerge and Thorp 2005; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). This species has been recorded as the host of Stylops elongata, a strepsipteran parasite (Kathirithamby and Taylor 2005).

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 blaisdelli 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. 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. Existing records from urban Los Angeles are 50 to 100 years old, and it is unclear if the habitat they were originally recorded in is still intact. The most recent records are from a habitat fragment embedded in a matrix of urban San Diego, and may face threats from degradation and fragmentation. 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 anatolis and alter other abiotic factors important for this species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena blaisdelli 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).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from Anza-Borrego Desert State Park, San Diego National Wildlife Refuge, US Forest Service Land (Cleveland, San Bernardino, and Sequoia National Forest), and the Mojave River Forks Regional Park, 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.