Andrena decolorata

Justification:
Andrena decolorata is a solitary bee that is known from fewer than 25 observations. It occurs in southern California, United States and northern Baja California Norte, Mexico. There is one unverified record of this species from 1934 from Colorado, which was not included in the analysis of this species. Using all verified observations, the extent of occurrence is 10,040 km2. This species has not been observed since 1972, so it is unclear if it is extant throughout its range. Andrena decolorata may occur in just six locations, if threats act independently on each documented locality. The species is likely a dietary specialist, collecting pollen from plants in the genus Camissonia (Onagraceae). It occurs in coastal sage scrub, a habitat that has been severely impacted by habitat loss, degradation, and fragmentation due to urbanization. This threat likely impacts species by reducing available ground nesting sites and abundance of host plants needed to provision nests. This species is likely also impacted by exposure to pesticides and climate change. Because this species is known from an extent of occurrence less than 20,000 km2, likely occurs in fewer than 10 locations, and has been subject to continuing decline observed and projected in the quality of its habitat, it is assessed as Vulnerable under B2abiii. More information is needed to determine if this species still occurs in its range, and to determine how threats to this species could be mitigated.

Food habits comment: Andrena decolorata is presumed to be a dietary specialist, visiting plants from the genus Camissonia (Onagraceae) for pollen. Habitat comment: This species has been recorded in shrubland, between 476 and 2639 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 and April (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Threat comments: Specific threats to this species have not been studied. However, climate change and drought, urbanization, and altered fire regime impact the quality of the habitat where this species occurs. Since 2000, the Southwest U.S. has seen the worst drought in 1,200 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 decolorata has a short adult life stage, emerges in spring, and appears to be a narrow pollen specialist of the plant Camissonia which blooms in response to winter rain, it may be at further risk from winter droughts within its range. 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 decolorata and alter other abiotic factors important for this species. Impacts from habitat loss, degradation, and fragmentation likely impact four locations for this species that are on private land. Of those, at least two may have been lost to urbanization. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena decolorata 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 needs No known conservation actions are in place for this species. Protected/Managed area comment: Observations of this species are known from US National Forest Service Land (San Bernadino) land, but this does not confer any specific protections to the species. This species has also been recorded from private land. 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.

Research need comment: More information is needed about the population status, population trend, existing threats, range limits, habitat, and ecology of this species. Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range.

(a. any taxonomic concerns about the validity of the species? b. any taxonomic revisions underway that would require a species reassessment.