Andrena palpalis

Justification:
The blue-phacelia mining bee (Andrena palpalis) is a pollen specialist solitary bee that occurs in the Mojave and Sonoran deserts of the southwestern United States and northwest Mexico. Using all known observations of this species, the extent of occurrence is 502,761 km2. The species has been described as relatively common, but there have been no rangewide studies that examine population trends. The species is likely impacted by the severe drought that is ongoing within its range. This drought likely limits the availability of the mostly annual, winter rain-responsive food plants on which this species relies. This impact is likely to be ongoing, as winter rain is expected to continue to decline due to climate change throughout the range of the species. More information is needed on the population trends, impact of threats, and range extent of this species. Although it may be threatened by climate change and drought, it has been recently observed across most of its range, and its large range may insulate it against stochastic fluctuations that could contribute to its extinction risk. As such it is assessed as Least Concern for now.

The blue-phacelia mining bee is a dietary specialist, visiting plants from the genus Phacelia (Boraginaceae) for pollen. It occurs in deserts and shrublands of the Sonoran and Mojave deserts, and the foothills of the California Coast Range. It has also been recorded from urban and suburban areas. 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 & 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 (Chesshire et al., 2023; LaBerge, 1985). Adults are assumed to emerge annually (Danforth et al., 2019).

Since 2000, the Southwest U.S. has seen the worst drought in 1200 years (Williams et al., 2022). Drought can reduce the abundance of flowering plants on a landscape scale, and also reduce pollen and nectar quality (Wilson Rankin et al., 2020). Drought conditions have been shown to reduce the diversity and abundance of native bees (Minckley et al. 2013, Hung et al. 2021). Drought may be particularly impactful to the blue-phacelia mining bee, as it specializes on mostly annual plants that bloom in response to winter rainfall, and show lower performance in dry years (Venable, 2007). Models for the region where the blue-phacelia mining bee occurs predict a continued decline in winter and spring rain (Gutzler & Robbins, 2011), potentially limiting the availability of food plants for the species. Certain aspects of this species' biology may make it more vulnerable to some threats. The blue-phacelia 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 & Paxton, 2009; Grab et al., 2019; Potts et al., 2010; Raven & Wagner, 2021; Wojcik et al., 2018).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from Bureau of Land Management (BLM), Forest Service, U.S. Fish and Wildlife Land, and National Park 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.