Andrena boronensis

Justification:
Andrena boronensis is a dietary specialist, solitary bee that occurs in Southern California, United States, and Baja California Norte, Mexico. Although there are over 500 records of this species, only 30 high quality digitized specimen records were available for analysis at the time of this writing. Using high quality records, the extent of occurrence is 162,619 km2. The species has not been observed since 2000, so it is unclear if the species still persists across its entire known range. Because of the limited availability of high quality data, it is unclear if recent search effort in the region has been sufficient to detect the species. Across its range, threats from climate change, exposure to pesticides, and habitat loss and degradation have been observed. These threats may be acting on the species at local levels. More information is needed to determine the range limits of the species, its population trend, and the degree to which threats are acting on the species. Because there is limited high quality data available, with no recent records of this species, it is assessed as Data Deficient for now. Existing records of the species should be digitized and made publicly available, and this species should be searched for in unidentified museum materials.

Andrena boronensis is a dietary specialist bee that collects pollen from the plant genus Camissonia (Onagraceae) to feed its larvae (LaBerge and Thorp 2005). Although females from this species have been observed foraging from a number of Camissonia species, they collect pollen almost exclusively from Camissonia campestris (Linsley et al. 1964). This species nests underground like all other Andrena (Danforth et al. 2019), with most nests documented near the hard-packed edges of unpaved roads (Linsley, MacSwain, and Raven 1964). Excavated nests measured 7 mm in diameter, with tunnels dug at a 45 degree angle to a depth of 11 - 14 cm, then vertically another 36 - 47 cm, where they progress horizontally 12 - 20 cm where the nest cell is located (Linsley, MacSwain, and Raven 1964). 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 to June (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). The strepsipteran parasite Stylops has been documented in Andrena boronensis (Linsley, MacSwain, and Raven 1964). Female Nomada bees, were also noted around the nest entrances of A. boronensis, and may parasitize nests (Linsley, MacSwain, and Raven 1964).

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). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena boronensis 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 Bureau of Land Management (BLM), 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. 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.