HOST SPECIFICITY OF DIFFERENT POPULATIONS OF THE LEAF BEETLE DIORHABDA ELONGATA (COLEOPTERA: CHRYSOMELIDAE), A BIOLOGICAL CONTROL AGENT OF SALTCEDAR (TAMARIX SPP.)

Authors: Milbrath, Lindsey; Deloach Jr, Culver

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2005
Publication Date: 1/3/2006
Citation: Milbrath, L.R., Deloach Jr, C.J. 2006. Host specificity of different populations of the leaf beetle diorhabda elongata (coleoptera: chrysomelidae), a biological control agent of saltcedar (tamarix spp.). Biological Control. 36:32-48.

Interpretive Summary: Saltcedars are exotic shrubs or trees that have invaded river systems throughout the Western U.S., causing major problems. A leaf-feeding beetle had previously been released to control saltcedar, but it only became established in northern areas of the U.S. Additional populations of the beetle that could establish in the Southwestern states were tested for their safety toward non-saltcedar plants. The beetles did not feed on any of the plants we tested except for some feeding on a small group of native shrubs. We anticipate little or no damage to these shrubs but significant damage to saltcedar. Control of saltcedar will improve native plant communities and wildlife habitat, and insure water supplies for agriculture and municipalities.

Technical Abstract: The leaf beetle, Diorhabda elongata (Brullé), was released in 2001 for the classical biological control of exotic saltcedars, a complex of four invasive Tamarix species and various hybrids. It did not establish at sites south of 37°N latitude where summer daylengths are below the critical photoperiod of the northern-adapted populations of the beetle. Therefore, we assessed the host specificity of four D. elongata populations collected from more southern latitudes in the Old World (Tunisia, Crete, Uzbekistan, and Turpan, China). All populations were similar to each other and the previously released populations of D. elongata in their host specificity. Larval/pupal survival for all populations was 34-100% on Tamarix, 0-76% on Frankenia (both in the order Tamaricales), and 0% on the remaining 28 species of plants on which all the larvae died as 1st instars. D. elongata laid more eggs on saltcedar, generally fewer eggs on athel except for Uzbekistan beetles, and few to no eggs on three species of Frankenia. Few to no adults were found on Frankenia plants which also were poor maintenance hosts. The release of any of the four D. elongata populations in the southern U.S. and northern Mexico should pose no risk to plants outside the order Tamaricales and a low risk to native, non-target Frankenia plants. Athel, a moderately valued evergreen species of Tamarix, may be less damaged than saltcedar. Any impact on non-target species must be weighed against the benefit to entire riparian ecosystems that will occur with the control of saltcedar.