Andrena linsleyi

Justification:
Andrena linsleyi is a narrow pollen specialist from the southwestern United States and northwestern Mexico. The bee specializes on the plant genus Oenothera, with most foraging records from Oenothera deltoides. Using all known records of the species, the extent of occurrence (EOO) is 407,874 km2. However, there is only one record of the species since 1983, and it has not been recorded overall since 2001. This is despite there being nearly five times as much recent search effort as was required to detect the species historically. Therefore, it is unclear whether the species persists throughout its entire range. Ongoing drought and other impacts from climate change may be limiting the availability of forage for this species. Additionally, impacts from urbanization have been observed within the range of this species, so it is possible that threats are acting on this species at a local level. More information is needed about this species persistence throughout its entire range, population trends, and threats. For now, it is assessed as Data Deficient.

Andrena linsleyi is a narrow pollen specialist that specializes on the pollen of the plant genus Oenothera (Onagraceae), especially Oenothera deltoides. This species apparently occupies only the southern portion of the range of Oenothera deltoides, so its range appears limited by ecological factors other than host plant availability. Oenothera deltoides is a night blooming species, and Andrena linsleyi usually collects remaining pollen early the following morning before the flowers close for the day (LaBerge and Thorp 2005). Andrena linsley occurs in the Sonoran and Mojave Deserts. This species makes its nest on declivities, and are constructed underground, with burrows descending vertically from a circular tumulus (LaBerge and Thorp 2005). 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). This species appears to be protandrous, with males emerging earlier in the season than females (LaBerge and Thorp 2005). Records of this species come from February through May, with most observations from March and April (LaBerge and Thorp 2005; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019). The presence of the parasite Stylops (Strepsiptera: Stylopidae) has been reported in Andrena linsleyi (LaBerge and Thorp 2005).

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 (Hung et al. 2021). Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena linsleyi 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 is a narrow 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 and 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).

No known conservation actions are in place for this species. Observations of this species are known from Bureau of Land Management (BLM) 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 better understand 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.

More information is needed about the population status, range limits, habitat, and ecology of this species.

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