The floral hosts and distribution of a supposed creosote bush specialist, Colletes stepheni Timberlake (Hymenoptera: Colletidae)

Abstract

Colletes stepheni Timberlake, previously thought to be a narrow oligolege of Larrea (creosote bush) of limited distribution in the Sonoran Desert, is found to be a much more widely distributed psammophile of the Sonoran, Mojave and Great Basin Deserts that utilizes two unrelated plant pollen sources, Larrea (Zygophyllaceae) and Psorothamnus (Fabaceae). The geologic history of the region suggests a potential host shift from the more ancient occupant, Psorothamnus, to the Neogene colonizer, Larrea.