Andrena balsamorhizae

Justification:
The Mojave gypsum bee (Andrena balsamorhizae) is known from 17 localities surrounding Lake Mead on the Arizona/Nevada border, in the United States. Using all known records, the extent of occurrence is 4,154 km2. The species is a narrow habitat specialist, using pollen from only the silverleaf sunray (Enceliopsis argophylla), and nesting only the gypsum soils its host occurs in. Its host plant is also considered by NatureServe to be imperiled. Because of this tight specialization, it is not likely that there are additional areas of suitable habitat beyond its extent of occurrence. This species probably occurs in just one location, defined as a single area where a threat could impact all individuals in the population. This single location is threatened by loss of habitat due to urban development, loss of host plants or potential for phenological mismatch due to climate change, and habitat degradation by recreational impacts, livestock, and gypsum mining within its range. There has already been at least one presumed local extinction, where a site that formerly hosted the species has been developed, and host plants no longer persist there. Therefore, this species qualifies as Endangered under criterion B1ab(iii, iv).

Distribution

Population

Habitats and Ecology

The Mojave gypsum bee is a very narrow pollen specialist that collects pollen solely from the plant species Enceliopsis argophylla. The species has been recorded from the Mojave Desert basin and the Arizona/New Mexico Plateau. This species nests underground, and is a nest substrate specialist, nesting only in gypsum soils (Griswold 2006). Nests of 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 before laying a single egg (Michener 2007). This species is active in the spring from March to early May and has a single generation per year, (Griswold et al. 2006; Chesshire et al. 2023). Based on data for other Andrena, adults are assumed to emerge annually (Danforth et al. 2019).

Habitat Types

Use and Trade

Threats

This species is threatened by ongoing drought and climate change. Since 2000, the Southwest US 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 quantity and quality (Wilson Rankin, Barney, and Lozano 2020). A recent study has shown reduced diversity and abundance of native bees under drought conditions (Hung et al. 2021). Because this species is a very narrow dietary specialist, it may be linked to higher risk of extinction due to reduced host lant availability, especially under climate change scenarios (Roberts et al. 2011) and reduced effective population sizes (Packer et al. 2005). Climate change can cause shifts in plant distribution and altered phenology (Cayan et al. 2001; Kelly and Goulden 2008; CaraDonna, Iler, and Inouye 2014). Variability in floral resource availability and phenological mismatch is especially impactful for the Mojave gypsum bee, which has such a narrow dietary breadth. Furthermore, its host plant, Enceliopsis argophylla itself is ranked by NatuerServe as imperiled due to its restricted range, substrate specificity, and threats from recreational use (NatureServe 2023). The majority of the habitat for this species is located in Clark County, which had the second largest county population growth in the United States in 2017 (Brean 2018). Much of this growth is in the urban-wildland interface, impacting remaining intact desert habitat. Populations of the Mojave gypsum bee and its host plant are likely impacted by recreational activities. The vast majority of observations of the Mojave gypsum bee come from the Lake Mead National Recreation Area (LMNRA), which is the 6th most visited park in the National Park Service, and was visited by 7.5 million people in 2019 (National Park Service 2020). Although off road vehicles (ORVs) are not permitted in LMNRA, nearby land under Bureau of Land Management (BLM) jurisdiction is heavily used by ORVs. Surrounding BLM land has both records of the Mojave gypsum bee (Chesshire et al. 2023) and its host plant Enceliopsis argophylla (SEINet Portal Network 2023) This recreational use compacts the soil, impacting nest site conditions, and can destroy populations of Enceliopsis argophylla. Several gypsum mines in the area threaten this species by direct destruction of the gypsum substrate this species relies on for nesting, and the removal of Enceliopsis argophylla. Both the Pabco Gypsum Mine, on private land, and Lima Nevada Gypsum Mine, on BLM land, are within five km of Mojave gypsum bee records. There has also been exploration for lithium resources on BLM land in the White Basin area, where gypsiferous soil occurs (Cornelisse et al. 2019). This exploration has contributed to approximately 5 acres of ground disturbance, which occurs within 10 km of records of the Mojave gypsum bee. Certain aspects of this species' biology may make it more vulnerable to some threats. The Mojave gypsum bee is a ground nesting species, and nests may be harmed by certain ground disturbing activities, which can kill bees nesting close to the surface (Williams et al. 2010). 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

No known conservation actions are in place for this species. The species has been recorded from the Lake Mead National Recreation Area, Bureau of Land Management land, the Hualapai Indian Reservation, The Valley of Fire State Park, as well as private land. Populations of this species that occur on the Lake Mead National Recreation Area and the Valley of Fire State Park are protected from impacts of ORV use, which is not allowed within the boundaries, however, these parks are open range, with some of the highest concentrations of wild burro in the region (Abella 2008) and abundant other trespass livestock. The species is listed on the BLM State Sensitive Species List for Nevada, and has been ranked as Imperiled in Nevada using NatureServe criteria. It has also been included as a Species of Greatest Conservation Need in the State Wildlife Action Plan by the Nevada Department of Wildlife, but specific conservation actions related to these statuses have not yet been outlined or implemented. Further research is needed to determine the overall size of the population and to identify trends and better understand existing threats. All known and potential sites where this species occurs should be protected from pesticides, habitat alteration, grazing, OHV and other potentially harmful recreational use, mining development, and any other threats that interfere with the habitat of this species. Additionally, populations of its host plant Enceliopsis should be protected, and this plant species should be included in habitat restoration efforts. Conservation efforts of the Mojave gypsum bee are likely to benefit the imperiled Mojave Poppy bee (Perdita meconis) which co-occurs with the Mojave gypsum bee.

Code	Threat	Timing	Scope	Severity
1	Residential & commercial development - 1.2. Commercial & industrial areas	Ongoing	Minority (<50%)	Unknown
1.1	Residential & commercial development - Housing & urban areas	Ongoing	Minority (<50%)	Unknown
1.2	Residential & commercial development - Commercial & industrial areas	Ongoing	Minority (<50%)	Unknown
2	Agriculture and aquaculture - Livestock farming and ranching -> Agro-industry grazing, ranching, or farming	Ongoing	Majority(50-90 %)	Causing/Could cause fluctuations
3	Energy production and mining	Ongoing	Minority (<50%)	Unknown
3.2	Energy production and mining - Mining and quarrying	Ongoing	Minority (<50%)	Unknown
6	Human intrusions and disturbance	Ongoing	Majority (50 -90%)	Unknown
6.1	Human intrusions and disturbance - Recreational activities	Ongoing	Majority (50 -90%)	Unknown
8	Invasive and other problematic species, genes, and diseases - 8.1 Invasive non-native/alien species/diseases -> 8.1.2. Named species	Ongoing	unknown	Unknown
8.1.2	Invasive and other problematic species, genes, and diseases - Named species	Ongoing	unknown	Unknown
9	Pollution - 9.3 Agricultural and forestry effluents -> 9.3.3 Herbicides and Pesticides	Ongoing	Minority (<50%)	Unknown
9.3.3	Pollution - Herbicides and Pesticides	Ongoing	Minority (<50%)	Unknown
11	Climate change & severe weather - 11.3.Temperature extremes	Ongoing	Minority (>90%)	Severity: Causing/Could cause fluctuations
11.1	Climate change & severe weather - Habitat shifting & alteration	Ongoing	Whole (>90%)	Causing/Could cause fluctuations
11.2	Climate change & severe weather - Droughts	Ongoing	Minority (>90%)	Severity: Causing/Could cause fluctuations
11.3	Climate change & severe weather - Temperature extremes	Ongoing	Minority (>90%)	Severity: Causing/Could cause fluctuations

Assessment