Andrena aquila

Justification:
Andrena aquila is a solitary bee species that is known from fewer than 10 records. Using all records of the species, the extent of occurrence (EOO) is 3,571 km2. There is a high degree of uncertainty in the EOO because it is generated with only five localities. Despite this, Andrena aquila has not been observed since 1969 from anywhere in its range, although it is unlikely that there has been sufficient search effort within its range to detect it. It is unclear if the species still persists throughout its entire known range. This species probably occurs in four locations, each representing an area where a single threat, such as urban development, severe wildfire and associated habitat alteration, or pesticide exposure could eliminate all individuals. More information is needed about the life history of this species, as well as its persistence in its range, population trend, and its threats. This species should be looked for in unidentified museum materials. Because this species has a small EOO, with active and ongoing environmental threats within its range, it is assessed as Endangered for now. This species should be reassessed if more data becomes available.

There is little information available about the habitat and ecology of this species due to extremely limited observations. The species has been collected foraging on Platystemon californicus (Papaveraceae), but its dietary breadth is not understood. 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 March to April (Laberge 1971; 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 1,200 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 occurs in California coastal sage scrub habitat, one of California's most threatened vegetation types, which is globally imperiled (NatureServe 2024). This habitat is highly threatened by modification, fragmentation, and loss due to urban and suburban growth. Nearly half of California’s residents live in the coastal California counties where this habitat occurs, which is less than 10% of the state’s land area (Riordan and Rundel 2013). Less than 20% of this habitat remains (Davis, Stine, and Stoms 1994), and the existing fragments are considered some of most valuable real estate in California. This contributes to considerable development pressure on remaining fragments, and their high real estate value makes their conservation costly. Coastal sage scrub has also been modified significantly in the past 100 years due to exotic annual grass invasion, which has been facilitated by increased wildfire frequency (Minnich and Dezzani 1998; Talluto and Suding 2008). These factors also contribute to a feedback where increased grass cover increases fire frequency, leading to grassland conversion. This habitat conversion may limit the availability of host plants used by Andrena aquila and alter other abiotic factors important for this species. This species also occurs at the edge of the San Joaquin Valley, where ecosystem modification due to agricultural intensification can impact bees. 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 aquila 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). 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 needs No known conservation actions are in place for this species. Observations of this species are known from Bureau of Land Management (BLM) and 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 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.

The description of this species states that it could be possible to consider this Andrena aquila a melanistic form or race of A. stipator or A. buccata, but there are no records of intermediate forms, and the characteristics of A. aquila make it difficult to squarely place it among the other species. The species author recommends that it is better considered its own separate species until there is more evidence. However, there are no apparent additional specimens of this species since it was authored, and it is unclear if this issue has been further investigated.