The Great Sunflower Project

Svastra – sunflower bees (family Apidae)
By Lisa Schonberg and Mace Vaughan (Xerces Society) and Gretchen LeBuhn (SFSU)

Genus summary: The genus Svastra is limited to the New World, and most species are North and Central American. There are about 15 species in the U.S. and Canada (Michener 2000), and 3 are known from New York State (Danforth & Magnacca 2002).

Floral relationships: There are some specialist foragers in this genus; two species specialize on plants in the willow herb family, and another specializes on cactus flowers (Michener 2000). Svastra obliqua is one of the most common and abundant species in the genus and occurs throughout the U.S. and in parts of Mexico and Canada (Rozen 1964). This species is important to agriculture; it is one of the most common pollinators of hybrid sunflower crops (Greenleaf & Kremen 2006).

Nesting habits: Most Svastra are solitary ground nesting bees. Some species nest communally, with two or more queens sharing a nest and each queen individually building and provisioning her own brood cells (Michener 1994). The Svastra female lines her brood cells with a waxlike material she secretes (O’Toole & Raw 1999).

Diagnostic characteristics: Svastra are moderate to large in size, and between 0.3 to 0.8 inches long; Svastra obliqua is one of the larger Svastra spp. (Greenleaf & Kremen 2006). Svastra spp. are hairy, with pale hair bands on their abdomen (Michener 2000). Their hairy legs are a conspicuous distinguishing character (Katharina’s doc). Females carry dry pollen on scopa on the upper part of their hind legs (Gretchen excel). Males have exceptionally long antennae.

Similar taxa: Svastra may be confused with Melissodes, but are usually significantly larger (Michener 2000).

Known conservation concerns:

Interesting fact: Greenleaf & Kremen (2006) found that the presence of wild bees, including Svastra 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 would stay within a row of male flowers, gathering pollen, and generally avoid the pollen-free female rows where they are needed for successful cross-pollination.

Additional resources: Pollination of sunflowers: Greenleaf & Kremen (2006).