Andrena piperi

Justification:
Piper’s mining bee (Andrena piperi) is a dietary specialist bee that visits plants from the family Brassicaceae for pollen. It occurs across much of the western United States, with some occurrences in northern Sonora, Mexico as well. Using all records, the extent of occurrence is 3,094,171 km2. Across the range of the species, impacts from climate change, drought, and pesticide use have been observed. These factors may be acting on the species at local levels. More information is needed to determine the impact of these threats at a population scale, and to track population trends. However, because the species is widespread, occurs in many habitat types, and can persist in human altered landscapes, it is unlikely that it is threatened with extinction at this time. Therefore, it is assessed as Least Concern.

Piper’s mining bee is a dietary specialist, visiting plants from the family Brassicaceae for pollen, including the genera Alyssum, Brassica, Capsella, and Sisymbrium (Timberlake 1951). Andrena piperi is commonly found in human-altered landscapes (Leong et al. 2016), as well as in the agricultural areas, deserts, grasslands, shrublands, and forests of the west. In a study examining pan trap color preference among bees, this species was found to prefer yellow pan traps source (Toler, Evans, and Tepedino 2005). 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 through July, with Most records from April and May (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats have not been identified for this species. However, 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). Certain aspects of this species' biology may make it more vulnerable to some threats. Piper’s mining bee 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), US Forest Service, US Fish and Wildlife, 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.