Technical Abstract: Diorhabda elongate (Brulle) sensu lato leaf beetles have been released in the United States for the classical biological control of invasive Tamarix L. species, which are exotic trees that are causing deterioration of riparian ecosystems in western North America. The impact of D. elongate defoliation on Tamarix nonstructural carbohydrates (NCHOs) was measured in both manipulative field cage and non-manipulative natural, experiments. Additionally, spring above-ground growth was measured following beetle defoliation in manipulative field cage experiments in Texas. There was no significant difference in the proportional change in NCHOs between beetle-damaged and undamaged control-treatment trees in the manipulative field cage experiment. However, spring above-ground regrowth was reduced by 35 percent on trees which experienced beetle defoliation the previous fall. In the natural experiment, root crown tissue was sampled in 2005 and 2006 from stands near Lovelocik, Nevada, in which trees had experienced 0-4 years of beetle defoliation. In 2005, mean NCHO concentrations were statistically different between tree stands and ranged from 9.0 +/- 0.8 percent (Mean +/- SE) in trees that had not been defoliated to 3.2 +/- 0.4 percent, 2.1 +/- 0.4 percent and 2.3 +/- 0.4 percent in trees in stands that had been defoliated for 1, 2 and 3 successive years, respectively. In 2006, NCHO concentrations were again statistically different between stands and ranged from 13.6 +/- 0.9 percent in trees that had not been defoliated to 7.6 +/- 0.8%, 2.3 +/- 0.4 percent, 1.5 +/- 0.3 percent and 1.7 +/- 0.4 percent in trees in stands that had been defoliated for 1, 2, 3 and 4 years, respectively. These results indicate that D. elongate herbivory reduces nonstructural carbohydrates and inhibits regrowth which may lead to reduced survival and reproduction of Tamarix.