Andrena capricornis

Justification:
Andrena capricornis is a spring-active, pollen specialist bee species that occurs in the deserts of the southwestern United States. Using all records for the species, the extent of occurrence is 1,289,389 km2. The only records from the last decade come from a significantly smaller area in southeast Arizona, an area of particularly high sampling effort for bees. Although concentrated recent records is likely an effect of higher sampling effort within this region, it is unknown if the species persists throughout its entire historic range. Additionally, spring months are less surveyed than summer months, which may contribute to knowledge gaps for this species. Within the range of the species, climate change impacts, increased urbanization and agricultural development have been observed, so it is possible that localized threats are acting on this species. Drought and variable precipitation due to climate change may be acting on the abundance of available host plants required by this species. Further research is needed to establish full details of population size, trends, and threats to the species. As such, this species is assessed as Data Deficient.

Andrena capricornis is a pollen specialist of plant species in the family Brassicaceae and found in the deserts of California, Arizona, New Mexico, and Texas (Ribble 1974). It has mostly been collected from the genus Physaria, but has also been observed foraging on Brassica and Descurainia as well as some genera from other plant families. Although this species has been described as a Brassicaceae specialist, it has been observed foraging from the flowers of the federally endangered Acuña cactus (Echinomastus erectocentrus var. acunensis) (Johnson 1992). The cactus is unlikely to make up a major part of the bee’s diet, as the range of A. capricornis extends well beyond the range of the Acuña cactus, but the bee species may warrant some conservation attention due to its association with the endangered cactus. This species likely nests underground as do all other Andrena (Danforth et al. 2019), but nests for 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 before laying a single egg (Michener 2007). This species has been observed from February to July, though the vast majority of records come from March and April (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 Physaria to bloom (Danforth et al. 2019). Habitat:

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 (Rankin, Barney, and Lozano 2020). Drought conditions have been shown to reduce the diversity and abundance of native bees (Minckley et al. 2013, Hung et al. 2021). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena capricornis 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). Although the host plants of this species can be abundant at times, many of the genera used by this species show reduced blooms in drought years, potentially impacting Andrena capricornis. 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).

No known conservation actions are in place for this species. Observations of this species are known from Bureau of Land Management (BLM), United States Forest Service Land, and United States Fish and Wildlife 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.

More surveys targeting this species throughout its historic range are needed to understand its persistence throughout its 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 has been documented to hybridize with A. scurra and A. arabis where they co-occur (Ribble 1974).