Defoliation by introduced Diorhabda elongata leaf beetles (Coleoptera: Chrysomelidae) reduces carbohydrate reserves and regrowth of Tamarix (Tamaricacceae)

Authors: HUDGEONS, JEREMY - TEXAS A&M RES EXT CTR; KNUTSON, ALLEN - TEXAS A&M RES EXT CTR; HEINZ, KEVIN - TEXAS A&M UNIV; Deloach Jr, Culver; DUDLEY, TOM - MARINE SCIENCE INSTITUTE; PATTISON, ROBERT - UNIV OF ALASKA; Kiniry, James

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2007
Publication Date: 8/15/2007
Citation: Hudgeons, J.L., Knutson, A.E., Heinz, K.M., Deloach Jr, C.J., Dudley, T.L., Pattison, R.R., Kiniry, J.R. 2007. Defoliation by introduced Diorhabda elongata leaf beetles (Coleoptera: Chrysomelidae) reduces carbohydrate reserves and regrowth of Tamarix (Tamaricacceae). Biological Control. 43(2):213-221.

Interpretive Summary: Diorhabda leaf beetles have been released in the United States for controlling invasive saltcedar, an exotic tree that causes deterioration of riparian ecosystems in western North America. The impact of insect defoliation on saltcedar nonstructural carbohydrates (NCHOs) was measured in both manipulative field cage and non-manipulative natural, experiments. Additionally, tree growth was measured in the spring 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 Lovelock, 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 percent in trees that had not been defoliated to 3.2 percent, 2.1 percent and 2.3 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 percent in trees that had not been defoliated to 7.6 percent, 2.3 percent, 1.5 percent and 1.7 percent in trees in stands that had been defoliated for 1, 2, 3 and 4 years, respectively. These results indicate that insect herbivory reduces nonstructural carbohydrates and inhibits regrowth which may lead to reduced survival and reproduction of saltcedar.

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.