Andrena parachalybea

Justification:
Andrena parachalybea is a possible dietary specialist solitary bee that visits the plant genus Camissonia (Onagraceae) for pollen. The species is only known from 22 records, and occurs in the southwest United States and northern Baja California. Using all known observations of this species, the extent of occurrence (EOO) is 65,613 km2. However, the only two records from western Arizona are from 1938, and it has not been observed there since. If the species no longer occurs there, the EOO is considerably smaller, and would meet criteria to be ranked as imperiled.. This species is likely threatened by drought and climate change, which limit the availability of its annual, winter rain-responsive host plant. Additional threats ongoing within the range of this species include urbanization, increased frequency and severity of wildfire, and exposure to pesticides. More information is needed to determine whether this bee still occurs throughout its known range and the extent to which threats impact the species. As such it is ranked Data Deficient for now.

Andrena parachalybea has been described as dietary specialist that visits plants from the genus Camissonia (Onagraceae) for pollen, and has been observed foraging from Camissonia campestris, C. bistorta, and C. cheiranthifolia (Thorp 1969). However, additional records from the Entomology Research Museum at the University of California, Riverside show that many females were collected from a floral resource other than Camissonia (D. Yanega, pers. comm. with Saff Killingsworth Jan 30 2024). Dietary breadth may be much wider than just one genus. Andrena parachalybea occurs in the warm deserts of the southwest United States. This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests from this species have not been described. The species constructs its nest in loose, sandy soils in close proximity to its host plants (Thorp 1969). 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 May (Chesshire et al. 2023). Adults are assumed to emerge annually, but they may remain in diapause as immatures in years of low rainfall. Many desert bee species are able to diapause for multiple years and synchronize their emergence when sufficient winter rains trigger floral hosts such as Camissonia to bloom (Danforth et al. 2019).

Since 2000, the Southwest U.S. has seen the worst drought in 1200 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 (Hung et al. 2021). Drought may be particularly impactful to Andrena parachalybea, as it specializes on annual plants that bloom in response to winter rainfall, and show lower performance in dry years (Venable 2007). Models for the region where the bee occurs predict a continued decline in winter and spring rain (Gutzler and Robbins 2011), potentially limiting the availability of food plants for the species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena parachalybea 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 Bureau of Land Management (BLM) and US 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 better understand 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. This species is closely related to Andrena chalybea. The revision of both species states that although there is no direct evidence of reproductive isolation, the ranges are mutually exclusive, and nesting substrate and dietary preferences differ between the species.