Andrena striatifrons

Justification:
Andrena striatifrons is a pollen specialist solitary bee that occurs in the western United States and southwest Canada. Using all records of the species, the extent of occurrence is 2,463,488 km2. The species has not been recorded since 2010 despite nearly 15 times as much recent search effort as was required to detect the species historically. The persistence of the species throughout its entire range is not well understood. It is most abundant in mountainous areas, and has been recorded in shrublands, forests, agricultural areas, and urban areas. The species visits plants from the genus Salix (Salicaceae) for pollen. Across the range of the species, impacts from climate change, exposure to pesticides, wildfire, and urbanization have been reported, which may be acting as threats at local levels. More information is needed to assess the impacts of these threats and to determine a population trend for the species. Because Andrena striatifrons is widespread, occurs in many different habitat types, and has been reported as common in at least one study, it is unlikely that it is threatened with extinction at this time. As such, it is assessed as Least Concern.

Andrena striatifrons is a dietary specialist that visits plants of the genus Salix (Salicaceae) for pollen (LaBerge 1973). The species was the most common bee visitor to Salix lasiolepis in a study of the plant’s pollination biology in Arizona (Sacchi and Price 1988). The species has also been collected in abundance from Taraxacum officinale (Asteraceae) in Nevada (LaBerge 1973). This species is most abundant in mountainous areas (LaBerge 1973). It has been recorded in shrublands, forests, agricultural areas, and urban areas. 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 February through July, but chiefly in April, May and June (LaBerge 1973; Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena striatifrons 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). This species has had its conservation status evaluated using NatureServe criteria at the U.S. state and Canadian province level in some areas where it occurs. It has been evaluated as Vulnerable in British Columbia, Canada.

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from Bureau of Land Management (BLM), United States Forest Service, and National Park Service 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.

Surveys targeting this species are needed throughout its range to determine its persistence throughout its historic range. 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.