Andrena bendensis

Justification:
Andrena bendensis is a pollen specialist solitary bee that visits plants from the genus Chrysothamnus (Asteraceae) for pollen. It occurs in the western United States, mostly in the Great Basin region. Using all records of the species, the extent of occurrence (EOO) is 313,926 km2, and the AOO 76 km2, although there is uncertainty in the size of the AOO. The species has not been observed anywhere in its range since 1965, although there has been approximately eight times the search effort throughout its EOO as was required to detect it historically. Throughout the range of the species, impacts from overgrazing, climate change, and pesticide exposure have been observed. These threats are likely impacting the quality of the habitat used by the species in at least four of the 16 locations for this species, with more locations potentially threatened by increasing lithium exploration within its range. Because this species is known from limited locations facing a variety of threats, has a small estimated AOO, and has not been seen since 1965, it is assessed as Near Threatened for now.

Distribution

Population

Habitats and Ecology

Specimens of this species used in the species description were collected only from Chryothamnus (Asteraceae) (Donovan 1977). This supports the possibility of dietary specialization in this species, although there are few records of this species overall. Further investigation of dietary breadth is warranted. The species has been collected in shrublands, grasslands, agricultural areas, and urban 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 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 August and September (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Habitat Types

Use and Trade

Threats

Much of the range of this species overlaps public grazing land, most of which is managed by the Bureau of Land Management (BLM). Thousands of acres of grazing land in this region has failed to meet the BLM’s own land health standards, with these failures attributed to overgrazing (BLM 2022). Overgrazing can contribute to negative impacts to bees through direct removal of forage that they rely on. In the Intermountain West where this species occurs, livestock grazing has also contributed to the invasion of the European annual grass species Bromus tectorum (cheatgrass) (Mack 1981), which can outcompete native forbs that bees rely on, and also contribute to a more frequent and severe fire regime than what occurred historically (Brooks and Chambers 2011). More frequent fire intervals may reduce the available forage of this species, as Chrysothamnus is typically top-killed by fire, and may take several years to begin flowering again (Kuntz 1982). Much of the range of this species is being explored for lithium extraction with proposed lithium mining projects as close as 28 km from a record of Andrena bendensis (Parker et al. 2022). Lithium mines, their infrastructure, and roads to access them can directly impact bees through habitat loss. Hydrological impacts from water use at mines can indirectly impact bees by depleting and polluting ground water, which can alter the abundance and composition of flowering plants used by foraging bees. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena bendensis 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 likely 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 Actions

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 United States Fish and Wildlife 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.

Code	Threat	Timing	Scope	Severity
1	Residential & commercial development - 1.2. Commercial & industrial areas	Ongoing	Minority (<50%)	Slow, significant declines
1.1	Residential & commercial development - Housing & urban areas	Ongoing	Minority (<50%)	Slow, significant declines
1.2	Residential & commercial development - Commercial & industrial areas	Ongoing	Minority (<50%)	Slow, significant declines
2	Agriculture and aquaculture - Livestock farming and ranching -> Agro-industry grazing, ranching, or farming	Ongoing	Minority (<50%)	Slow, significant declines
2.1.3	Agriculture & aquaculture - Agro-industry farming	Ongoing	Minority (<50%)	Slow, significant declines
7	Natural system modifications - 7.1. Fire & fire suppression -> 7.1.2. Suppression in fire frequency/intensity	Ongoing	Majority (50 - 90%)	Causing/Could cause fluctuations
7.1.1	Natural system modifications - Increase in fire frequency/intensity	Ongoing	Majority (50 - 90%)	Causing/Could cause fluctuations
8	Invasive and other problematic species, genes, and diseases - 8.1 Invasive non-native/alien species/diseases -> 8.1.2. Named species	Ongoing	Minority (<50%)	Slow, significant declines
8.1.2	Invasive and other problematic species, genes, and diseases - Named species	Ongoing	Minority (<50%)	Slow, significant declines
9	Pollution - 9.3 Agricultural and forestry effluents -> 9.3.3 Herbicides and Pesticides	Ongoing	Minority (<50%)	Slow, significant declines
9.3.3	Pollution - Herbicides and Pesticides	Ongoing	Minority (<50%)	Slow, significant declines
11	Climate change & severe weather - 11.3.Temperature extremes	Ongoing	Majority (50 - 90 %)	Slow, significant declines
11.1	Climate change & severe weather - Habitat shifting & alteration	Ongoing	Majority (50 - 90 %)	Slow, significant declines
11.2	Climate change & severe weather - Droughts	Ongoing	Majority (50 - 90 %)	Slow, significant declines
11.3	Climate change & severe weather - Temperature extremes	Ongoing	Majority (50 - 90 %)	Slow, significant declines

Assessment