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Bug Spotlight!

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U.C. Riverside
Department of Entomology
Photo by: Photos by David Hawks 
Xeralictus bicuspidariae (Hymenoptera: Halictidae)

 Photos by David Hawks, text by Doug Yanega

 In March, 2001, while visiting the Kofa National Wildlife Refuge (upper left photo) south of Quartzsite, Arizona, we discovered a previously unappreciated aspect of a floral mimicry system involving two plants, Mentzelia involucrata (family Loasaceae) and Mohavea confertiflora (family Scrophulariaceae). The two plants are fairly similar in size, shape, and color, and commonly grow in proximity to one another (upper right photo). It has long been recognized that the Mohavea is a mimic of the Mentzelia, as some of the bees that visit the Mentzelia for pollen will also visit the Mohavea, where they cannot collect pollen. In particular, there are two rare species of bees in the genus Xeralictus, one of which, X. bicuspidariae, occurs on the eastern side of the Colorado River, the other on the west. What wasn't recognized previously was that the mimicry of Mohavea involves tricking male Xeralictus into thinking there are females in the flowers. An empty Mentzelia flower is entirely yellow (leftmost lower photo), and patrolling male Xeralictus fly right past them. However, when a female Xeralictus visits the flower, she buries her head in the flower, leaving only the tip of her abdomen exposed amidst the anthers (second lower photo). Patrolling males pounce on females while they're in this vulnerable position, and attempt to mate. The Mohavea flowers have a dark central marking that is almost the exact size and color of a female Xeralictus abdomen (third lower photo). A patrolling male will dive into the flower, but instead of him encountering a female as he obviously expects, the trap-like flower deposits a yellow stripe of pollen on the top of his thorax, where he cannot remove it (rightmost lower photo). The pollen is carried to the next Mohavea flower, so the plant achieves pollination without sacrificing any nectar or pollen to the bees.

                               

(c)2006  ERM-UC Riverside