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Diadasia


Photo by Hartmut Wisch

Diadasia- Sunflower bees (family Apidae)
by Lisa Schonberg and Mace Vaughan (Xerces Society) and Gretchen LeBuhn (SFSU)

Genus summary: Diadasia is a very diverse genus restricted to the New World. About 30 species occur in North America (Michener 2000), mostly in the western states, with about 6 species in the northwestern portions of both the U.S. and Canada (Stephen et al. 1969). Diadasia usually fly in the mornings and early afternoons (Stephens et al.).

Floral relationships: Many Diadasia spp. are specialist foragers on particular plant taxa, including the genus Helianthus and families Cactaceae, Malvaceae, and Onagraceae. They are also referred to as “sunflower bees” because some species are important pollinators of hybrid sunflower crops (Greenleaf & Kremen 2006).

Nesting habits: Diadasia are solitary nesters, and some species often nest in large aggregations. Diadasia make relatively shallow nests in the ground, often with turreted nest entrances (gretchen). Nests are relatively shallow, sometimes in large aggregations. Diadasia may soften the earth with nectar in preparation for nest excavation (Michener 2000).

Diagnostic characteristics: There is a wide diversity of appearances within Diadasia. Most species are small to medium sized, 0.2 to 0.9 inches long, and robust and hairy. Diadasia females carry pollen in very large scopa (brushes of hair) on their hind legs. Some species have distinctly banded abdomens, while others’ abdomens have a uniform covering of pale hair. Unlike some other Eucera, Diadasia males do not have very long antennae (Michener 2000).

Similar taxa: Diadasia superficially resemble other genera in the Tribe Eucerini, such as Peponapis, Melissodes, and Svastra (Michener 2000).

Known conservation concerns: Diadasia species are important pollinators of hybrid sunflower crops. Pollination rates by Diadasia and other native bees decline with increasing distance of crops from natural habitat. Thus, intensification of agriculture and elimination of nearby habitat can be detrimental to populations of Diadasia spp. and other native bees (Greenleaf & Kremen 2006).

Interesting Fact: Greenleaf & Kremen (2006) found that the presence of wild bees, including Diadasia spp., greatly enhanced the effectiveness of honey bees (Apis mellifera) as pollinators. Honey bees and native bees avoid each other, and as a result honey bees move more often between the rows of male (pollen producing) and female (hybrid seed producing) flowers. Were native bees not present, pollen-foraging honey bees move more often along a row of male flowers, as they gather pollen, and generally avoid the pollen-free female rows where they are needed for successful cross-pollination.

Additional resources: pollination: Greenleaf & Kremen (2006)

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