We initially observed native stem-boring beetles (Amphicerus bicaudatus) feeding on stems of invasive tamarisks (Tamarix) at Bonny State Park, Yuma County, in eastern Colorado. At 11 sites in Colorado, Nebraska, and Kansas, we examined tamarisks and the most common co-occurring native tree, eastern cottonwoods (Populus deltoides), for the occurrence of this beetle. We detected evidence of feeding and development of insects at nine of the sites and in 112 of 579 tamarisks. Among sites, A. bicaudatus occurred in nearly 20% of tamarisks. Only 13 of 480 eastern cottonwoods showed signs of activity by A. bicaudatus. During dissections of stems of tamarisks, nearly 90% of adult beetles were in live versus dead stems.