Andrena blennospermatis

Justification:
Andrena blennospermatis is a solitary bee that occurs in the vernal pool habitat of central California, United States. It is known from approximately 50 observations and approximately 18 localities, only 10 of which are suspected to be extant. These 10 localities may represent 10 locations if each is separately impacted by localized threats to the species. Using all observations of the species, the extent of occurrence (EOO) is 30,332 km2, and the area of occurrence (AOO) is 64 km2. Andrena blennospermatis is a dietary specialist, collecting pollen only from the plant genus Blennosperma to feed its offspring. Forage of the bee includes Blennosperma bakeri, a federally listed endangered species, known from very few localities overall. The host plants for the bee are vernal pool obligates, which is a rare and declining ecosystem, threatened by habitat loss, fragmentation, and degradation due to urban development and agricultural expansion, alterations to hydrology, exotic species invasion, and climate change. Threats to this habitat also impact this bee. The bee is directly threatened by mosquito abatement activities in vernal pool systems, where application of insecticides have lethal and sublethal impacts on the bee. These threats contribute to a serious risk of extinction for this species. Due to the small AOO of this species, the continued decline in the area and quality of its habitat, low number of locations, and the loss of at least eight localities to development where this species has been observed historically, it is ranked as Endangered B2ab(iii,iv).

Distribution

Population

Habitats and Ecology

Andrena blennospermatis is a dietary specialist that collects pollen from the plant genus Blennosperma including Blennosperma nanum and Blennosperma bakeri (Asteraceae), which are vernal pool obligate plants (Joan M. Leong, Randolph, and Thorp 1995). Blennosperma bakeri is a federally endangered plant species, and occurs in just one California county (U.S. Fish and Wildlife Service 2016). Blennosperma seed set in a potted array was significantly reduced where the Andrena blennospermatis was absent (J. M. Leong 1994). In a study of foraging behaviour of this species, limited foraging between patches of the host plant was observed, and although the spatial relationship between Andrena blennospermatis and forage was not specifically investigated, marked bees were not found foraging far from their nests (Joan M. Leong, Randolph, and Thorp 1995). This may be due to limited dispersal capability of the species. Females have been recorded foraging in the middle of the day (Thorp 1969). This species likely nests underground like all other Andrena (Danforth et al. 2019), but nests from this species have not been described. Females excavate nest sites in upland areas surrounding vernal pools (Brown et al. 2022). 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). Records of this species come from February to April (Thorp 1969; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). In one pan trap study, this bee was detected in yellow pan traps, but not white or blue (Joan M. Leong and Thorp 1999).

Habitat Types

Use and Trade

Threats

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). Urbanization and irrigation with recycled water has contributed to at least two locality extirpations of Blennosperma bakeri (USFWS 2016). One of the host plants of this bee, Blennosperma bakeri is listed as federally endangered within the United States, and is known from 18 extant occurrences, and five extirpated or possibly extirpated sites (U.S. Fish and Wildlife Service 2016). It occurs in just one California county, where its habitat has been fragmented, degraded, or lost due to urbanization. Loss, degradation, and fragmentation of this habitat, combined with localized plant populations with limited dispersal capacity, limits the abundance of the host plant Andrena blennospermatis relies on, and limits available forage for the species. The species has been recorded in constructed vernal pool sites (Gilmore 2018), but may not be able to disperse to mitigation sites due to its very low observed dispersal distance (Joan M. Leong, Randolph, and Thorp 1995). Andrena blennospermatis is also directly threatened by mosquito abatement programs that occur in the vernal pool systems. 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 Blennosperma bakeri 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 blennospermatis 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 blennospermatis 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 (M. J. F. Brown and Paxton 2009; Potts et al. 2010; Wojcik et al. 2018; Grab et al. 2019; Raven and Wagner 2021).

Conservation Actions

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from U.S. Forest Service land (Mendocino National Forest, Eldorado National Forest) and United States Fish and Wildlife (North Central Valley Wildlife Management Area) 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.

Code	Threat	Timing	Scope	Severity
1	Residential & commercial development - 1.2. Commercial & industrial areas	Ongoing	Majority (50-90%)	Slow, significant declines
1.1	Residential & commercial development - Housing & urban areas	Ongoing	Majority (50-90%)	Slow, significant declines
1.2	Residential & commercial development - Commercial & industrial areas	Ongoing	Majority (50-90%)	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