C. Jack DeLoach, Ph.D.
Research Entomologist
USDA/ARS
Grasslands/Soil/Water Research Laboratory

Abstract

Exotic saltcedars (primarily Tamarix ramosissima), small trees from Eurasia, have heavily invaded western riparian ecosystems since the 1920s. Anthropogenic modifications of abiotic factors have contributed to the invasion, but biotic factors - synergistic interaction with the abiotic modifications, direct competition, and the lack of indigenous natural enemies - are also important. Saltcedar probably exacerbates most mortality factors of the Southwestern Willow Flycatcher (Empidonax traillii extimus), reducing reproductive success by half. The flycatcher nests extensively in saltcedar in Arizona, but only occasionally in neighboring states; this probably is caused by the highly desirable branching structure of saltcedar that in some areas acts as a super-normal stimulus. Biological control, by introducing the insects that regulate saltcedar abundance in Asia, is a viable option to provide environmentally compatible, permanent, and inexpensive control. An Asian leafbeetle, Diorhabda elongata, was tested at Temple, TX and Albany, CA; both adults and larvae heavily damaged saltcedar. The larvae also fed a lesser amount on the native desert shrubs, Frankenia spp., but the adults were not attracted to these plants nor to lay eggs on them; it is not expected to significantly affect Frankenia in nature. Those beetles were not attracted to and could not develop on any other native plant species. The U.S. Fish and Wildlife Service has provided a Letter of Concurrence for experimental field releases of D. elongata at sites more than 200 miles from where the Willow Flycatcher nests in saltcedar; the beetles were released in May 2001. Extensive monitoring of the effects of these releases on plant and animal communities is now underway and will be conducted for several years.