Diorhabda carinulata, the northern tamarisk beetle, was released in 2001 into the western United States for the biological control of invasive riparian shrubs in the genus Tamarix, or saltcedar or tamarisk (DeLoach et al., 2003). Beetles have dispersed southward from a few initial release sites (Fig. 2) (D. W. Bean et al., 2012) following remote riparian corridors, which likely represent independent dispersal pathways. The D. carinulata range expansion provides an excellent study system for testing the predictions of range expansion theory because original release sites are known and the range expansion has been monitored (D. Bean & Dudley, 2018).