Andrena crudeni

Justification:
Andrena crudeni is a solitary bee that occurs in California, United States, from the San Francisco Bay area east to the Sierra Nevada mountain range, south to San Diego. Using all records, the extent of occurrence is 108,476 km2. The species has been recorded as common, or abundant in some sites in some years, but overall, no study has evaluated the population status of this species range-wide. Andrena crudeni is a dietary specialist, using pollen from the genus Nemophila (Boraginaceae) to provision nests. This specialization may be as narrow as just one species, Nemophila menziesii. Across the range of this species, impacts from climate change, drought, habitat loss and degradation, and exposure to pesticides. These threats may be acting on the species at local levels. More information is needed to assess the population trend of this species across its range, and the degree to which threats are influencing the population trend. Because this species is relatively widespread, occurs in several habitat types, and has been described as locally common, it is unlikely that it is threatened with extinction at this time. As such, it is assessed as Least Concern for now.

Distribution

Population

Habitats and Ecology

Food habits comment: Andrena crudeni is a dietary specialist that collects pollen from the genus Nemophila (Boraginaceae). It is possibly restricted to collecting pollen from just one species, Nemophila menziesii (Cruden 1972). The species has been recorded foraging on Platystemon and Limnanthes when the pollen of Nemophila is in short supply (Cruden 1972). Habitat comment: This species has been recorded in grasslands, shrublands, mixed forest, and evergreen forest, between 82 and 2325 m. Reproduction comment: 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). Phenology comment: Records of this species come from March through June, with most records from April and May (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Habitat Types

Use and Trade

Threats

Threat comments: Specific threats to this species have not been identified. Since 2000, the Southwest U.S. has seen the worst drought in 1200 years (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). Because Andrena crudeni has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of the plant Nemophila menziesii, which blooms in response to winter rain, it may be at further risk from winter droughts within its range. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena crudeni 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 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). Threats Threats:

Conservation Actions

Conservation needs No known conservation actions are in place for this species. Protected/Managed area comment: Observations of this species are known from Bureau of Land Management (BLM), National Park Service, and United States Forest Service land, but this does not confer any specific protections to the species. Management comment: 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
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	Minority (<50%)	Slow, significant declines
7.1.1	Natural system modifications - Increase in fire frequency/intensity	Ongoing	Minority (<50%)	Slow, significant declines
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	Minority (<50%)	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	Minority (<50%)	Slow, significant declines
11.3	Climate change & severe weather - Temperature extremes	Ongoing	Minority (<50%)	Slow, significant declines

Assessment