Andrena monticola

Justification:
Andrena monticola is a pollen specialist bee that occurs throughout much of central Mexico and into southeast Arizona, United States. Using all known records of the species, the extent of occurrence is 487,366 km2. The species has not been observed since 2013, when it was recorded throughout much of its known range in Mexico. However, it has not been observed in the U.S since 1964 despite high search effort in the region it is known to occupy. It is unclear if the species persists in all parts of its historic range. Across the range of the species, threats associated with climate change, drought, and deforestation have been observed, so it is possible that these are impacting the species at local scales. More research is needed to determine range extent, persistence, population trends and threats to this species. However, because it is widespread and occurs in several different habitat types, it is unlikely that it is threatened with extinction at this time. As such, it is assessed as Least Concern for now.

There is little information available about the habitats and ecology of Andrena monticola. The species is a pollen specialist species within the plant family Asteraceae, having been observed foraging at the genera Solidago, Heliopsis, and Cirsium. Records of this species come from the oak and pine forests, and the deserts and xeric shrublands of the Chihuahuan desert and Apache highlands. 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 July through October, with most records from August and September (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

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. Andrena monticola 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 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 and 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).

No known conservation actions are in place for this species. Observations of this species are known from federal and state protected land in Mexico, as well as United States Forest 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 are needed across the known range of this species, especially in the U.S., where it has not been recently observed. 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.