|Deloach Jr, Culver|
Submitted to: Biological Control Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: December 16, 2004
Publication Date: February 28, 2005
Citation: DeLoach, C.J. 2004. Research on biological control of saltcedar in the United States, with implications for cooperation with Mexico. In: Memoria del XV Curso Nacional de Control Biologico, November 8-13, 2004, Los Mochis, Mexico. p. 204-217. Interpretive Summary: Saltcedars are small trees native in central Asia and the Mediterranean area that were introduced into the western United States in 1823. They have cedar-like foliage and clusters of small, pink attractive flowers on the ends of the branches; they are deep-rooted and tolerant of drought, fires, salty soils and are not damaged by North American insects. They have displaced the native plants on about 2 million acres of valuable bottomland along streams and lakeshores in arid areas, where they use large quantities of scarce water needed for agriculture, cities and homes, damage wildlife habitat, harm over 40 threatened and endangered species of native animals and plants, and interfer with recreational use of parks and natural areas. Through cooperators in France, Israel, China, Kazakhstan and Turkmenistan, we carefully tested several saltcedar feeding insects in quarantine at Temple, TX and Albany, CA. After proving their safety and obtaining official authorizations, we released a leaf-beetle, Diorhabda elongata from northwestern China and eastern Kazakhstan into the open environment in 1999 in Nevada, Utah, Colorado and Wyoming. These beetles are increasing and spreading rapidly and by August 2004 had defoliated from 80 to 2000 ha of saltcedar at the different sites. In 2003, we released similar Diorhabda beetles from Crete, Greece in Texas and New Mexico which now have successfully overwintered and in 2004 began defoliating saltcedars at Big Spring, TX and Artesia, NM. However, in our tests, these Crete beetles (as also the China/Kazakhstan beetles had done), slightly damaged Tamarix aphylla, called athel in the U.S. and pinabete in Mexico, a large, evergreen tree also introduced from southern Asia and North Africa, that is used in the southern U.S. and northern Mexico as a shade tree or as windbreaks. Discussion and cooperative research is underway between U.S. and Mexico scientists to resolve the conflict between the great value of controlling saltcedar and the small value of athel as a shade tree, and to obtain Mexican agreement to release the Diorhabda beetles along the Rio Grande/Rio Bravo between Mexico and Texas. Resolving this issue will permit control of saltcedar in southern areas and thereby facilitate the recovery of native riparian plant communities, improve wildlife and fish habitat, reduce wildfires, increase availability of water, and increase recreational usage of parks and natural areas.
Technical Abstract: Biological control has successfully controlled 10 exotic, invasive weeds of rangelands and natural ecosystems in the United States since 1945, and control of others is in progress. We initiated biological control of saltcedar (Tamarix spp.) in 1987, using host-specific insect herbivores that regulate saltcedar populations in the Old World. We did a risk analysis, including the possible effects of biological control on the endangered southwestern willow flycatcher (Empidonax trailii extimus), which had begun nesting extensively in saltcedar in Arizona. Our cooperators in France, Israel, Kazakhstan, China and Turkmenistan tested 20 candidate control insects. Then, after quarantine testing, we released the first of these, the leaf beetle Diorhabda elongata Brulle from China and Kazakhstan, into field cages at 10 approved sites in 6 states in 1999 and into the open environment in May 2001. These beetles established at 5 sites in Nevada, Utah, Colorado and Wyoming and defoliated from 40 to 600 ha at each site by late June 2004. However, these beetles failed to establish in Texas and southern California because short summer daylengths stimulated premature diapause and failure to overwinter. In 2002, our overseas cooperators sent Diorhabda biotypes from four southern latitudes. After quarantine testing, we released some of these biotypes into field cages and then into the open environment at 5 sites in Texas, 2 in New Mexico, and 2 in California during late 2003 and 2004. They overwintered well, are increasing in population, and have begun defoliating saltcedar at 2 sites but have encountered heavy predation in some areas; intensive monitoring is underway. Biological control can provide self-sustaining, permanent, safe, and low cost control of saltcedars. This will allow recovery of native riparian plant communities, improved wildlife and fish habitat, reduced wildfires, increased availability of water, and increased recreational usage of parks and natural areas.