Andrena duboisi

Justification:
Andrena duboisi is a solitary bee that occurs in California, United States, from the San Francisco Bay area south to the Los Angeles Area east of the Sierra Nevada mountain range. Using all records of the species, the extent of occurrence is 99,037 km2. It has not been observed anywhere in its range since 2008, so it is unclear if the species is extant throughout its entire known range. The species occurs in grasslands and vernal pool systems of California, which is a threatened ecosystem. It is a dietary specialist that visits plants from the family Asteraceae, with a potentially even more restricted diet. It has been documented foraging from several imperiled plant species. This species is threatened by the loss, degradation, and fragmentation of its vernal pool habitat, which impacts the availability of its host plants. It is also threatened by climate change, which may impact the hydrology of its vernal pool habitat and impact the quality and quantity of available forage. It is also likely threatened by exposure to pesticides, which may occur through mosquito abatement programs that occasionally take place in vernal pool systems. More information is needed to determine if this species is still extant throughout its known range, to understand a population trend for this species, and to determine the degree to which threats are acting on the population. Rank Sentence.

Food habits comment: Andrena duboisi appears to be a dietary specialist that visits plants from the family Asteraceae, possibly further restricted to the tribe Madieae. This species has been recorded as a pollinator of the imperiled plant species Layia heterotricha and Layia jonesii (Buchmann, Adams, and Howell, A, Weiss, M 2010). This species has also been called a vernal pool flower specialist, using plants from the genus Lasthenia for pollen (Spencer et al. 2006), including the endemic and rare Lasthenia conjugans (Thorp and LaBerge 2006). Habitat comment: This species has been recorded in vernal pools and grasslands, between 4 and 1,050 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 May (Chesshire et al. 2023; Thorp and LaBerge 2006). Adults are assumed to emerge annually (Danforth et al. 2019).

Threat comments: This species may be threatened by the loss of vernal pool habitat where its host plants occur. These habitats are made up of discrete, ephemeral wetlands, and are characterized by their impervious substrate that collects winter precipitation that dries out over the course of the summer (Holland 2009). In California, the Central Valley vernal pool ecosystem has declined 95% from its historic extent (Dahl 1990). Much of the remaining vernal pool habitat occurs in areas with high pressure from urbanization and agricultural expansion, which is expected to continue. Vernal pool habitat is also threatened by alteration of hydrology, which can happen either through droughts, which are predicted to become more frequent and severe across the range of the species (Franklin and MacDonald 2024), or via increased irrigation with reclaimed water. In some sites where the host plant occurs, increased water in vernal pool sites has occurred via agricultural runoff. Increased water or irrigation at the wrong time of year can kill host plants, and can contain pollutants such as herbicide and excess nutrients, which can kill host plants and encourage invasion of exotic species (USFWS 2016). Multiple host plants of this species are threatened with extinction themselves, including Layia heterotricha and L. jonesii (both NatureServe ranked G2S2 in California), and Lasthenia conjugans (NatureServe ranked G1S1 in California, federally listed by United States Fish and Wildlife Service as Endangered under the Endangered Species Act). Loss, degradation, and fragmentation of this habitat, combined with localized plant populations with limited dispersal capacity, limits the abundance of the host plant Andrena duboisi relies on, and limits available forage for the species. Andrena duboisi may be threatened by mosquito abatement programs, which can occur in vernal pool systems, althoug the magnitude of this threat depends on the application timing, amount, and chemical used in mosquito abatement programs, which is not information readily available at the time of this writing. However, documentation regarding the recovery of a vernal pool plant Blennosperma bakeri, which co-occurs with the host plants of Andrena duboisi, describes impacts from mosquito abatement vehicles driving through the plant population area while spraying for mosquitos in 2014 (USFWS 2016). Application of insecticides to the habitat of Andrena duboisi may cause lethal and sublethal effects to the species, impacting its population size, and contributes to its risk of extinction. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena duboisi 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: There are no observations of this species from federally managed land. It is known from some conservation lands, including the Bear Valley Conservation Area (American Land Conservancy) and Mount Diablo State Park (California Department of Parks and Recreation). 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.