Andrena baeriae

Justification:
Andrena baeriae is a pollen specialist bee that visits plants from the family Asteraceae to gather pollen. It occurs in California, United States, from the San Francisco Bay Area south to San Diego. Using all known records of the species, the extent of occurrence is 145,293 km2. There are limited records of the species since 2013, which come from near the Bay Area, and from the Channel Islands. This species has been abundant in some collection events, and rare in others. This species has a narrow dietary breadth and its floral hosts are associated with rare and vanishing vernal pool habitat, making it vulnerable to additional habitat loss or degradation. Across the range of the species, impacts from habitat loss and modification due to urbanization, climate change, and exposure to pesticides have been observed. These may be acting on the species at local levels. More information is needed to determine the impacts of these threats and to describe a population trend. However, because the species is somewhat widespread and occurs in several habitat types, it is unlikely that it is threatened with extinction at this time. As such it is assessed as Least Concern.

Andrena baeriae is likely a dietary specialist within Asteraceae, with foraging possibly further restricted within the genera Lasthenia (formerly Baeria) and Layia (Thorp and LaBerge 2006). This species has been recorded as a pollinator for two globally imperiled plants, Layia heterotricha and Layia jonesii (Buchmann, Adams, and Howell, A, Weiss, M 2010). It has been recorded in grasslands, shrublands, forests, agricultural and urban areas. In these areas, it is found in vicinity to vernal pools, where its host plants occur (J. Ascher, pers. comm. with S. Killingsworth 1 May 2024). 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 to July, with most records from March to May (Thorp and LaBerge 2006; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

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). This species may be threatened by the loss of vernal pool habitat where its host plants occur. These habitats are made up of discrete, ephemeral wetlands, and are characterized by their impervious substrate that collects winter precipitation that dries out over the course of the summer (Holland 2009). In California, the Central Valley vernal pool ecosystem has declined 95% from its historic extent (Dahl 1990). This landscape is threatened by urbanization and agricultural expansion combined with the localized plant populations with limited dispersal capacity. Loss and degradation of this habitat limits the abundance of the host plant Andrena baeriae relies on, and limits available forage for the species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena baeriae 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 United States National Forest and National Park 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. Conservation actions tailored to this species should focus on the conservation of vernal pool habitat and other habitat types where this species’ host plants occur. 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.