Andrena submoesta

Justification:
Andrena submoesta is a dietary specialist solitary bee that visits plants from the genus Lasthenia (Asteraceae) for pollen. It relies chiefly on Lasthenia burkei, a federally endangered plant, where the species overlap. It has been observed in the grasslands, shrublands, and woodlands from the Central Valley, Mojave Desert, and Coast Range of California. Using all known observations of the species, the extent of occurrence is 340,118 km2. Although the species was observed in one locality in 2016, there are few recent observations of the species overall. Across the range of the species, impacts from climate change, drought, and exposure to pesticides have been observed, and may be acting on the species at local levels. More information is needed to determine the impacts of these threats, as well as general population trends and life history information for the species. Because Andrena submoesta is widespread and occurs in several habitat types, it is unlikely that it is threatened by extinction at this time. As such, it is assessed as Least Concern for now.

Andrena submoesta is a dietary specialist bee species that visits plants from the Lasthenia (Asteraceae) for pollen (Thorp 1969). Lasthenia burkei, a major food source for A. submoesta, is a vernal pool obligate, and federally listed under the Endangered Species Act as endangered (USFWS 2016). The bee is apparently dependent on the L. burkei as a food source, but the plant apparently attracts other potential pollinators besides A. submoesta (US Fish and Wildlife Service 2014). The bee occurs in grasslands, shrublands, mixed forest, urban areas of California’s Central Valley, Coast Range, and Mojave Desert. 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 (J. H. Cane 1981) that serves to both isolate the provision from pathogens in the surrounding soil and to regulate water uptake from the soil atmosphere (James H. 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 February through June, although chiefly from April (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 (Minckley, Roulston, and Williams 2013; Hung et al. 2021). This species may be impacted by agricultural intensification, including high exposure to pesticides where it occurs in California’s Central Valley. The Central Valley of California is one of the most intensively farmed regions in the U.S.(Katibah 1984). An estimated 71% of the Central California Valley ecoregion is devoted to agriculture (Soulard and Wilson 2015). This species may be impacted by high exposure to pesticides where it occurs in the Central Valley. This region has some of the nation’s highest pesticide inputs, which can be detected in non-target plant species, sometimes in insect-lethal concentrations, across all land use types (Halsch et al. 2020). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena submoesta 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 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).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from 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 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.