Andrena rozeni

Justification:
Andrena rozeni is a narrow dietary specialist solitary bee species that occurs in deserts of the southwestern United States. There is some degree of uncertainty in the range of this species, which has several questionable records, from Washington State as well as northern Mexico. Using the most plausible records, the extent of occurrence for this species is 449,946 km2. The true range and extent of occurrence warrant further investigation. There are limited records of this species overall, and none since 2000, despite over four times the recent search effort as was required to detect this species prior to 2013. The species is a narrow pollen specialist, collecting pollen only from Camissonia claviformis, a spring blooming annual from the family Onagraceae. Across the range of the species, drought and climate change may be impacting host plant availability of this species. Other threats include urbanization and exposure to pesticides. More information is needed to assess the status of this bee throughout its range. As such, it is assessed as Data Deficient.

Andrena rozeni is a dietary specialist bee that visits plants from the genus Cammisonia for pollen. The primary recorded floral associate, Camissonia claviformis, extends beyond the known range of the bee species. This bee is mostly crepuscular, due to the bloom time of its host plant. Limited collection during this time of day may contribute to the lack of recent records of this species. The bee has been recorded in grasslands and shrublands in the Sonoran, Chihuahuan, and Mojave deserts. This species has been recorded building nests in the open, in small depressions or at the bottom of shaded road cuts. Nests consist of an “L” shaped main burrow, and can be as deep as 100 cm in sandy soil (Youssef and Bohart 1968). 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 February through May, with most records from March and April, although records from Mexico are from August, and may be erroneous (LaBerge and Thorp 2005; 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 US 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 rozeni has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of Camissonia claviformis, which blooms in response to winter rain, it may be at further risk from winter droughts within its range. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena rozeni 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 narrow 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), US Forest Service, 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 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.