Andrena afimbriat

Justification:
Andrena afimbriata is a solitary bee that occurs in central Texas, United States, and is known from fewer than 10 observations. Using all records, the element of occurrence (EOO) for this species is 106 km2, although this is constructed from just three localities that are arranged in a fairly linear distribution. The discovery of additional localities could potentially significantly increase the EOO. However, this species has not been observed since 1953 despite some bee collection in the area during the appropriate flight period. The species occurs in the vicinity of Austin, TX, a city that has seen major growth and urbanization in the last several decades. Impacts from urbanization may limit the host plants used by this species, as well as limit suitable nesting sites. Additionally, threats from fire regime change may be acting on this species, with effects including plant community shifts and increased severity of wildfires. Exposure to pesticides from the cotton, corn, and hay cultivation in the area may also be causing lethal and sublethal effects for this species. These threats, coupled with the small extent of occurrences, lack of recent records, and apparent rarity of the species overall, contributes to significant extinction risk for this species. As such it is assessed as Endangered.

Distribution

Population

Habitats and Ecology

Andrena afimbriata has been recorded in a region dominated by shrubland, and urban and agricultural areas of the south central semi-arid prairies and southeastern plains of Texas, United States. The few records of this species have been collected in what are now suburban environments, including highway rights of way, residential areas. It is unclear what land use type these localities were when they were collected in the 1950s. This species has been described as a dietary specialist, visiting plants from the family Asteraceae for pollen (Larkin, Neff, and Simpson 2008). However, this is based on only four samples, so the dietary breadth of this species may be wider. 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 April (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). * 3. Shrubland * 3.4. Shrubland –Temperate * 14 Artificial - Terrestrial * 14.1 Arable Land * 14.2 Pastureland * 14.5 Urban Areas

Habitat Types

Use and Trade

Threats

Specific threats to this species have not been investigated. However, there are environmental factors and land uses within the range of the species that may contribute to its risk of extinction, including climate change and drought, habitat loss due to urbanization and agricultural intensification, exposure to pesticides in residential and agricultural areas, and fire regime change. Since 2000, the Southwest U.S. has seen the worst drought in 1200 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). Central Texas is a mosaic of agricultural land uses, including cotton, corn, and hay production. In 2019, nearly 40,000 kg of neonicotinoid insecticide was applied to these crops in Texas (Weiben 2021). While many insecticides pose risk to bees, neonicotinoids are highlighted as a particular threat due to high toxicity to bees, multiple exposure routes, and persistence in the environment. Agricultural pesticides used on these crops may contribute to mortality as well as other sublethal effects for Andrena afimbriata. The region around Austin, Texas, where this species occurs, has been the fastest growing city in the United States for 12 consecutive years (Valencia 2023). Surrounding areas have seen impacts from increased urbanization (Zhao, Weng, and Hersperger 2020), some of which have occurred in environmentally critical areas (Kharel 2011). Land use change resulting from urbanization may impact Andrena afimbriata by limiting host plant availability, suitable nesting sites, and by contributing to habitat fragmentation. Additionally, increased urbanization within its habitat increases the potential for contact with pesticides used in residential settings, which can cause lethal and sublethal effects for this species. The region where this species occurs was historically subject to a fire interval of between one and 12 years, which maintained plant diversity and landscape physiognomy (Stambaugh, Sparks, and Abadir 2014). Woody plant invasion and other vegetation community changes occurred with fire cessation (Stambaugh, Sparks, and Abadir 2014). Most of Texas is at least moderately departed from historic vegetation assemblages (Hann et al. 2004), due to fire and other land use change. Although little is known about the dietary breadth of Andrena afimbriata, vegetation community shifts due to fire regime change may impact this species by altering the availability and assemblages of forage plants. In 2011, a high severity wildfire, totalling nearly 130 km2 occurred within the EOO of the species (Stambaugh et al. 2017), which may have impacted its host plant availability and potentially nest sites. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena afimbriata 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). This species may be 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).

Conservation Actions

Conservation needs No known conservation actions are in place for this species. Observations of this species come only from residential areas and road edges, offering no protection to the species, Andrena afimbriata likely also occurs within other lands, but these have not been documented yet. 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. Conservation measures should focus on characterizing the habitat used by this species, and protecting it from habitat loss and modification due to urban expansion and agricultural use. Measures to manage fire in alignment with the historical fire regime should take into account the host plant use of this species, and make efforts to encourage host plant diversity and abundance. In general, 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	Minority (<50%)	Slow, significant declines
2	Agriculture and aquaculture - Livestock farming and ranching -> Agro-industry grazing, ranching, or 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	Majority (50 - 90%)	Causing/Could cause fluctuations
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
9	Pollution - 9.3 Agricultural and forestry effluents -> 9.3.3 Herbicides and Pesticides	Ongoing	Minority (<50%)	Slow, significant declines
11	Climate change & severe weather - 11.3.Temperature extremes	Ongoing	Majority (50 - 90 %)	Slow, significant declines

Assessment