Andrena angelesia

Justification:
Andrena angelesia is a dietary specialist solitary bee species that occurs in southern California, United States. Using all records of the species, the extent of occurrence is 5,276 km2. However, the species has only been observed in one locality (two individuals in 1996) since 1950. The species has not been recorded anywhere in its range since 1996. This species occurs in a globally imperiled ecosystem, which is threatened by climate change, urban and suburban development, and an altered fire regime which contributes to ecosystem conversion. With the exception of the record from 1996, all other records come from small habitat fragments, or urban areas developed after the species record was recorded. It is unclear if the species persists in urban localities. This species is a narrow dietary specialist, visiting plants from the genus Platystemon (Papaveraceae) for pollen. This narrow specialization is especially vulnerable to climate change and drought, which is likely to alter the phenology and abundance of this bee’s host plant. This species probably occurs in one location, with the entire population threatened by high urban development pressure that could eliminate all individuals, and habitat degradation due to exotic species invasion and altered fire regime. High host plant and habitat specificity, ongoing threats to the ecosystem in which it occurs, and a small extent of occurrence all contribute to considerable risk of extinction for this species. As such, it is assessed as Vulnerable.

There is limited published information on the habitat and ecology of Andrena angelesia. The species occurs in California coastal sage scrub, a globally imperiled landscape (NatureServe 2024). This species has been described as a dietary specialist, collecting pollen exclusively from the plant genus Platystemon (Papaveraceae) (Timberlake 1951). 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 (J. H. Cane 1981) that serves to both isolate the provision from pathogens in the surrounding soil and to regulate water uptake from the soil atmosphere (James H. 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 May, with most records from April (Timberlake 1951; 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 (A. P. 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 angelesia has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of the plant Platystemon 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 angelesia and alter other abiotic factors important for this species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena angelesia 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 (N. M. 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 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. Because this species occurs in a California coastal sage scrub, which has experienced loss, degradation, and fragmentation, conservation efforts geared toward protecting and restoring this threatened habitat type. Populations of Platystemon should be protected and included in restoration efforts. 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.