Species in the genera Diadasia and Svastra are collectively called sunflower bees because, along with several other groups of plants, they are sunflower (Helianthus annuus) specialists. In addition to sunflowers, these bees specialize on mallows (Malvaceae), cacti (Cactaceae), evening primroses and willow herbs (Onagraceae), and wild bindweeds (Convolvulaceae). In fact, several cacti and mallows rely on sunflower bees for pollination services. Sunflower bees are found throughout the New World and generally are hairy bees. Males have long antennae.

Sunflower crops are typically planted in rows - pollen-producing male plants in one row, nectar-producing female plants in another. In order for pollination to occur, pollen must be moved from male plants to female plants by pollinators, primarily bees. Honey bees (Apis mellifera) are often used to pollinate sunflower crops, but worker honey bees specialize in either collecting pollen or nectar and primarily visit only one type of row. However, the presence of native bees, like sunflower bees, causes honey bees to change their foraging activity - the native bees chase the honey bees between the rows of sunflowers, making them up to five times more efficient pollinators, increasing seed set from three to 15 seeds produced per honey bee visit. In fact, research by Sarah S. Greenleaf and Claire Kremen has shown that the only sunflower fields to achieve 100% pollination are those fields with abundant native bee populations. The most important of these native bee species are long-horned (Melissodes spp.) and sunflower (Diadasia and Svastra spp.) bees. In this study, pollination by native bees accounted for only 7% of total pollination, but they were indirectly responsible for an additional 40% of pollination by alternating honey bee behavior.

References: Celebrating Wildflowers: Globe Mallow Bee (Diadasia diminuta), Vince Tepidino, US Forest Service; Saguaro Cactus Bees (Diadasia opuntiae), Saguaro Juniper Corporation; Native Bee Pollination of Hybrid Sunflowers, Xerces Society; Wild bees enhance honey bees' pollination of hybrid sunflowers, S. S. Greenleaf and Claire Kremen, Proceedings of the Natural Academy of Sciences, Vol. 103, No. 37, September 12, 2006, pp. 13890-13895; The Great Sunflower Project, The Great Sunflower Project; Chapter 9: Crop Plants and Exotic Plants, S. E. McGregor In Insect Pollination Of Cultivated Crop Plants, 1976.