Andrena chapmanae

Justification:
Andrena chapmanae is a solitary bee species that occurs in the western United States. There is little information available about the habitat and ecology of this species. Using all observations, its extent of occurrence is 1,015,618 km2, and its area of occurrence is 280 km2. Although this species has an AOO low enough to qualify for an imperiled ranking, it is known from many locations. However, the number of locations where this species still occurs is not well understood, as the species has not been observed since 2007. In the recent time period (since 2013), there has been approximately seven times as much search effort in its extent of occurrence as was required to detect it historically. Thus, its absence is not due to insufficient search effort. More surveys are needed to determine if this species persists throughout its known range. Across the range of the species, impacts from large-scale wildfire and drought have been observed, and may be acting on the species at local levels. More information is needed to understand its population trend, and to determine the role these threats have in the stability of this species. Because the species is widespread, and occurs in several habitat types, it is unlikely that it is threatened with extinction at this time. As such, it is assessed as RANK.

There is limited habitat and ecology information available for Andrena chapmanae. The dietary breadth of this species is not well understood. While it has been most commonly observed foraging from plants within the family Boraginaceae, it has also been recorded from Rosaceae and Salicaceae (Ribble 1974). It has been recorded from forests, shrublands, and occasionally grasslands. 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 August, with most records from May and June (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats to this species have not been investigated, although part of its range has faced major drought, which may impact habitat quality and resource availability. 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). Drought conditions have been shown to reduce the diversity and abundance of native bees (Minckley, Roulston, and Williams 2013; Hung et al. 2021). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena chapmanae 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 may be 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), United States 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 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.