Andrena annectens

Justification:
Andrena annectens is a solitary bee species that occurs in central California, United States. Using all observations of the species, its extent of occurrence is 21,222 km2. This species is only known from 19 observations, with only one extant locality recorded since 1998. This observation was from 2011 and comes from Pinnacles National Park. Although search effort for bees within the range of the species is not comprehensive, there have been over 5,200 observations of bees from within the extent of occurrence of the species during the appropriate phenological window. This species occurs in a globally imperiled ecosystem, the California coastal sage scrub. This ecosystem is threatened with habitat loss and modification due to urbanization and agricultural development, altered fire regime and invasion by exotic species, and climate change. Additionally, this species may be at risk of exposure to pesticides, which are widely used in the agricultural areas of California’s central valley. This species likely occurs in three locations, with each location subject to a different threatening event that could eliminate the entire population. Because of its small range size, few locations, and ongoing threats across its range, this species faces a risk of extinction. Because it does not meet the EOO threshold of 20,000 km2, it is evaluated as Near Threatened for now.

There is little information available about the habitats and ecology of this species. The description of this species lists Salix (Salicaceae) as a forage plant for this species (Ribble 1968). The dietary breadth of this species is not well understood. It has been recorded in grasslands, shrublands, urban, and agricultural 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 (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 March through June, with most records from April (Chesshire et al. 2023). Adults are assumed to emerge annually (Danforth et al. 2019).

Specific threats to this species have not been investigated. However, there are several ecological threats that occur within the range of the species that may threaten the species with extinction. These include climate change and drought, habitat loss and modification as a result of agricultural intensification, and exposure to pesticides. Additionally, this species occurs in a threatened habitat. 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). This species may be impacted by agricultural intensification, including high exposure to pesticides where it occurs in California’s Central Valley. The Central Valley of California is one of the most intensively farmed regions in the U.S.(Katibah 1984). An estimated 71% of the Central California Valley ecoregion is devoted to agriculture (Soulard and Wilson 2015). This species may be impacted by high exposure to pesticides where it occurs in the Central Valley. This region has some of the nation’s highest pesticide inputs, which can be detected in non-target plant species, sometimes in insect-lethal concentrations, across all land use types (Halsch et al. 2020). This species occurs in California coastal sage scrub habitat, one of California's most threatened vegetation types, which is globally imperiled (NatureServe 2024). This habitat is highly threatened by modification, fragmentation, and loss due to urban and suburban growth. Nearly half of California’s residents live in the coastal California counties where this habitat occurs, which is less than 10% of the state’s land area (Riordan and Rundel 2013). Less than 20% of this habitat remains (Davis, Stine, and Stoms 1994), and the existing fragments are considered some of most valuable real estate in California. This contributes to considerable development pressure on remaining fragments, and their high real estate value makes their conservation costly. Coastal sage scrub has also been modified significantly in the past 100 years due to exotic annual grass invasion, which has been facilitated by increased wildfire frequency (Minnich and Dezzani 1998; Talluto and Suding 2008). These factors also contribute to a feedback where increased grass cover increases fire frequency, leading to grassland conversion. This habitat conversion may limit the availability of host plants used by Andrena annectens and alter other abiotic factors important for this species. Certain aspects of this species' biology may make it more vulnerable to some threats. Andrena annectens 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). 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 U.S. Forest Service land 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. Because this species occurs in a California coastal sage scrub, which has experienced loss, degradation, and fragmentation, conservation efforts geared toward protecting and restoring this threatened habitat type. In agricultural areas where this species occurs, use of insecticides should be avoided. 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.