Lasioglossum sisymbrii

Accurate identification of L. sisymbrii requires specialized taxonomic expertise and microscopic examination. The species belongs to the subgenus Dialictus, which contains hundreds of morphologically similar species. Key characters include details of male genitalia, wing venation, and punctation patterns on the head and thorax. Bowl trap samples containing numerous small halictids frequently include this species, but it cannot be reliably distinguished from congeners without expert identification. It may be separated from some sympatric Lasioglossum by its association with specific host plants, though this is not definitive.

Found in dry, open habitats including prairies, meadows, and disturbed areas where host plants in the mustard family occur. Associated with foothill and montane environments in western North America. Nests in soil, with females excavating individual burrows.

Western North America, ranging from British Columbia and Washington south through Oregon, California, and into the southwestern United States. Distribution records also indicate presence in Middle America. The species occurs primarily west of the Rocky Mountains, with records from the Cascade Range, Sierra Nevada, and coastal regions.

Adult activity period corresponds with bloom of mustard family host plants, typically spring through early summer. In lower elevations, active from late February through June; at higher elevations, flight period extends into summer months. Exact phenology varies with local climate conditions.

Adults feed on nectar and collect pollen from flowers, particularly those of tansy-mustard (Descurainia spp.) and related Brassicaceae. The common name reflects this documented association with Sisymbrium and Descurainia host plants.

• Descurainia spp. - Pollen sourceTansy-mustard; primary host plant for pollen collection
• Sisymbrium spp. - Pollen sourceHedge mustards; documented host plants
• Arabis spp. - Possible pollen sourceRock-cresses; related mustards that may be visited

Solitary or weakly social nesting biology typical of many Lasioglossum species. Females excavate nest burrows in soil, provisioning individual cells with pollen and nectar. Development includes egg, larval, and pupal stages within the nest. Detailed life history specific to this species has not been documented.

Females are ground-nesting and collect pollen and nectar to provision brood cells. Males patrol for females, often at flowers or nesting aggregations. Like other small halictids, individuals are frequently captured in pan traps, suggesting attraction to visual cues. Foraging behavior is tied to mustard family bloom phenology.

Pollinator of early spring wildflowers in the mustard family, contributing to plant reproduction in dry meadow and prairie ecosystems. As a common and abundant species in many western habitats, it likely provides significant pollination services within its flight season. Serves as host for parasitic insects including strepsipterans, though specific parasite records for this species are not documented.

Contributes to pollination of native plants and potentially some crop species. Frequently encountered in bee biodiversity surveys and monitoring programs using bowl traps, where it represents a substantial portion of captures. The species illustrates challenges in bee monitoring: it is abundant in trap samples but requires taxonomic expertise to identify, creating logistical burdens for researchers processing large collections.

• Other Lasioglossum (Dialictus) speciesHundreds of morphologically similar small dark sweat bees in the same subgenus; require microscopic examination and specialized keys for separation.
• Halictus rubicundusAnother common sweat bee, but larger with distinct pale abdominal bands; more robust build and different facial markings.
• Agapostemon speciesBright metallic green or blue sweat bees; striking coloration absent in L. sisymbrii.
• Syrphidae (hover flies)Small flies frequently mistaken for sweat bees by casual observers; have single pair of wings (vs. two in bees), large eyes, and different antennae.

• pollinator
• ground-nesting
• spring-active
• mustard-specialist
• western North America
• halictid
• sweat bee
• bee monitoring challenge

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
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