|Deloach Jr, Culver|
Submitted to: Chihuahuan Desert Symposium
Publication Type: Proceedings
Publication Acceptance Date: 2/13/2006
Publication Date: N/A
Interpretive Summary: Saltcedars (Tamarix spp.), small trees native in the Old World, are causing great environmental harm in riparian areas of the western United States since their introduction in 1823. Today, they occupy about 2 million acres of prime bottomlands along streams and lakeshores where they have displaced native plant communities, degraded wildlife habitat, use large quantities of scarce water needed for agricultural irrigation and municipalities, increase wildfires and soil salinity, and interfere with recreational usage of parks and natural areas. We began a biological control program in 1986 by introducing the insects that regulate saltcedar abundance in its homeland, and after 10 years of testing in quarantine at Temple, TX and Albany, CA, we released a leaf beetle, Diorhabda elongata, into the open field at 10 sites in 6 western states in May 2001. By late summer 2004, this beetle had defoliated from 200 to over 5000 acres at each of 5 sites in Nevada, Utah, Colorado and Wyoming, but it was not effective in more southern areas. During 2003 and 2004, we released similar beetles from Crete, Greece at several sites in Texas and New Mexico; by August 2004, they were established in the open field and had begun defoliating saltcedar at Big Spring, TX and Artesia, NM. These beetles promise a high level of saltcedar control that is permanent, environmentally friendly, non-damaging to other plants, and inexpensive.
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 saltcedars (Tamarix spp.) in 1986, 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 Brullé 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 80 to 2000 ha at each site by September 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 4 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.