Adult Mediterranean tamarisk beetles, Diorhabda elongate (Brullé), a defoliator of exotic saltcedar (Tamarix spp.), were released into four field cages containing small saltcedar trees or closely-related exotic athel trees (Tamarix aphylla (L.) Karsten) and onto uncaged beneficial mature athel trees at sites in south Texas. In field cages, egg, larval, and adult densities per meter of green foliage were equal on saltcedar and athel in the first 8 weeks after release, but numbers of eggs, larvae, and adults were at least two-fold more on saltcedar. During this time, the beetles reduced green foliage by 50% on athel and by 20% on saltcedar. However, athel green foliage recovered after 10 weeks, while saltcedar foliage continued to decline. At two roadside field sites containing mature athel and no saltcedar, D. elongata adults were released in bagged athel branches in July 2006 and May 2007 and produced larvae that defoliated the branches by the third week after infestation. A few larvae and adults were found on unbagged athel branches during the first 3 months after release, but beetles failed to become established on athel trees and removed no more than 3% of green foliage from athel branches, which remained >85% green for 2 years. The Mediterranean tamarisk beetle thus did not colonize or cause permanent disfiguring damage to athel trees.