Tamarix biological control in North America [Chapter 28]
The biological control program targeting Tamarix spp. began in the 1970s with the goal of reducing the shrub’s negative impacts on riparian biodiversity and ecosystem function in western North America. Field releases of host-specific Diorhabda beetles started in 2001, leading to widespread defoliation within two years in many areas. These releases set off complex interactions among Tamarix, its associated herbivores, and varying environmental conditions across the western U.S. While defoliation often reduced evapotranspiration and opened canopies that supported growth of native vegetation, establishment of beetles failed in some areas due to unsuitable host species, mismatched environmental cues affecting diapause, or predation by generalist insectivores. In regions like Texas, populations were short-lived and Tamarix suppression was not sustained, whereas in other locations beetles initially reached outbreak densities before declining to moderate levels, resulting in patchy defoliation and limited long-term mortality of the target plant. These outcomes highlight both the short-term impacts of Diorhabda releases and the potential need for additional host-specific agents to achieve more effective and lasting control.
Gaffke, A. M., T. L. Dudley, D. W. Bean, G. M. Drus, M. J. Johnson, A. E. Knutson, D. K. Weaver, S. E. Sing, B. K. Orr, and D. C. Thompson. 2022. Tamarix Biological Control in North America, pp. 329–355. In: Van Driesche, R. G., R. L. Winston, T. M. Perring, and V. M. Lopez (eds.). Contributions of Classical Biological Control to the U.S. Food Security, Forestry, and Biodiversity. FHAAST-2019-05. USDA Forest Service, Morgantown, West Virginia, USA. https://research.fs.usda.gov/treesearch/64656.