Andrena caerulea

Andrena caerulea is a solitary bee that occurs in evergreen forests, shrubland, agricultural and urban areas. In the San Francisco Bay Area of California, where the species was studied extensively (Linsley and MacSwain 1959), it was found collecting pollen exclusively from Ranunculus californicus (Ranunculaceae), but there are exceptions among specimens across the entire range. LaBerge and Ribble (1975) suggest that the species is a dietary specialist of Ranunculus, and Ranunculus californica is the most important host plant, but the bee visits other species of plants more frequently on the periphery of its range. 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). Records of this species come from February through July, with most observations from April through June (Laberge and Ribble 1975; Chesshire et al. 2023). As this species spans a wide elevational gradient, the flight period is typically later higher in elevation, with apparently only one generation that is active for approximately one month (Linsley and MacSwain 1959). Adults are assumed to emerge annually (Danforth et al. 2019). The parasite Stylops pacifica has been recorded from A. caerulea specimens from Oregon and California, but only reach higher levels of parasitism (10%) in specimens from the Berkeley, CA vicinity (Laberge and Ribble 1975; Linsley and MacSwain 1959). Other enemies of the species were described in Linsley and Macswain (1959), and include Nomada opacella, N. obscurella, a Myopa conopid fly, myrmithid nematode, Xysticus sp. (spider), and fungus.

Specific threats to this species have not been described. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena caerulea 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).

Conservation needs No known conservation actions are in place for this species. Observations of this species are known from United States Forest Service, United States Fish and Wildlife, 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 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.