Persistence of an imperiled specialist bee and its rare host plant in a protected area

Abstract

Abstract The Mojave Desert of the southwestern U.S. is home to two protected species of poppy in the genus Arctomecon Torr. & Frém. (Papaveraceae). A pollinator of these species is the specialist bee Perdita meconis Griswold (Andrenidae) a specialist on poppy pollen. Recently, the easternmost population of P. meconis, which was associated with A. humilis Coville in Utah, has become locally extinct, and other historically associated bee pollinators have become scarce. Implicated in the disruption of this pollination system is invasion by the Africanised honey bee. Here we report on the status of P. meconis in historic populations associated with congener A. californica Torr. & Frém., 100 km west in Clark Co., Nevada where the Africanised honey bee is also adventive. We surveyed flower visitors at eight A. californica populations in 2017, six of which had been surveyed in 1995. In general, we found no disruptions of the historic pollination system of A. californica despite the presence of abundant Africanised honey bees, which largely foraged at other flower species. The most likely cause of the disparate effects of the Africanised honey bee in Utah and Nevada is livestock grazing. Grazing in Utah has been continuous for over three decades and while cattle do not graze A. humilis, they graze its floral competitors, forcing honey bees to forage on poppy flowers. In Nevada, protections afforded to the desert tortoise halted grazing approximately when the Africanised honey bee invaded, making diverse floral forage available for honey bees.