Andrena chromotricha

Justification:
The pigmented miner bee (Andrena chromotricha) is a broad pollen specialist bee that visits plants from the family Asteraceae for pollen. It occurs in the Great Lakes, Mountain West, and Southwest regions of the United States, but this species has not been recorded in the western part of its range since 1982. Although this absence may be attributed to lack of survey effort throughout its range, this lack of observation warrants more attention. Using all known records of this species, the extent of occurrence is 3,441,903 km2. Across the range of the species, climate change impacts, urbanization, and land use change has been observed, so it is possible that these threats are acting on this species at a local level. Because this species is widespread and occurs in many different habitats, it is reasonable to assume it is not threatened with extinction at this time, but more information is needed about the persistence of this species throughout its entire range to understand its extinction risk. As such, it is assessed as Data Deficient.

The pigmented miner bee visits only plant species in the species-rich family Asteraceae so may be considered a broad pollen specialist (Wood and Roberts 2018). It has been observed in prairies and grasslands in the Great Plains region (Sheffield, Frier, and Dumesh 2014; Leone et al. 2022), as well as Great Lakes coastal regions and forest transition zones (Wolf and and Ascher 2009) This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests of 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). The adult flight period for this species is July through September (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Western populations of this species may be threatened with climate change impacts. 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). A recent study has shown reduced diversity and abundance of native bees under drought conditions (Hung et al. 2021). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena chromotricha 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 oligolectic, 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). This species has had its conservation status evaluated using NatureServe criteria at the U.S. state level in some areas where it occurs. It has been evaluated as Imperiled in New York, Critically Imperiled in Vermont, and Possibly Extirpated in North Carolina.

No known conservation actions are in place for this species. Observations of this species are known from United States Forest Service (USFS) 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 should be conducted, especially in the western part of its range, where it hasn’t been recently recorded. 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?):