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FuEDEI Researchers Explore Solutions to Controlling Invasive Saltcedar

Saltcedar (Tamarix spp.) is a genus of old world plants that are highly invasive along waterways, mainly in arid areas. They tend to consume vast quantities of water in these water-deprived areas and salinize the soil in the process. Saltcedar was the target of a successful biocontrol project in North America that involved the introduction of a leaf beetle known as the tamarisk beetle (Diorhabda sp.).

In 2019, the Foundation for the Study of Invasive Species (FuEDEI) formed a consortium with other institutions in Argentina, and initiated a classical biological control program against saltcedar in Argentina, where the plant threatens to invade a huge area of the country’s territory. The consortium works closely with the USDA-ARS Western Regional Research Center in Albany, California, and the Department of Forest Ecosystems & Society at Oregon State University.

The first steps in the Argentine project were to sample local saltcedar populations and native Frankenia spp. (the plant’s closest relatives on the American continents) to obtain a list of native and exotic pathogens, insects, and other organisms that feed on or use these species in any way. This minimizes the chances of finding resistance in the future, and confirms whether biocontrol is a sound approach to the problem.

So far, several generalist insect species, including three native ones that are pests on fruit trees (Figure 1), and an old-world leafhopper, Opsius stactogalus, that is assumed to have been introduced with the plant have been identified. Recently, two fungal pathogens were found growing on saltcedars in central Argentina. Both fungal species have been cited in the old world on saltcedar, suggesting they were introduced with the plant.

Interestingly, these organisms have not been found on native Frankenia species (Figure 2), and the Frankenia insects have not been found on saltcedar. Furthermore, our observations indicate that none of these insects produce any significant damage on saltcedar, and the fact that some of them are pests suggests saltcedar may be acting as reservoir for orchard pests. The fungi were found not to significantly impact this invasive tree either.

Wax scales and bagworms — Figure 1. Wax scales and bagworm moths, the same that attack many fruit trees, are frequently found on saltcedar in Argentina. (Photo courtesy of the Foundation for the Study of Invasive Species (FuEDEI))

In summary, no native insects impact saltcedar in any significant way nor do the introduced organisms. Finally, none of the species that feed on native relatives of saltcedar have switched to the invasive plant. Our results warrant continuing with the original plan to introduce tamarisk beetles from North America, because the preliminary conditions have so far been met.

Figure 2. Frankenia juniperoides is one of the few native plants distantly related to the saltcedars. It is a small, perennial plant that grows in salt marshes up to 10 cm. (Photo courtesy of the Foundation for the Study of Invasive Species (FuEDEI))

Larvae formed by unidentified moth feeding on Frankenia juniperoides — Figure 3. Unidentified moth found feeding on Frankenia juniperoides: top, the larvae (about 6 mm long) form a shelter among the branches with silk while it feeds and develops (bottom). (Photo courtesy of Foundation for the Study of Invasive Species (FuEDEI))

branches with silk while it moth feeds and develops — Figure 3. Unidentified moth found feeding on Frankenia juniperoides: top, the larvae (about 6 mm long) form a shelter among the branches with silk while it feeds and develops (bottom). (Photo courtesy of Foundation for the Study of Invasive Species (FuEDEI))

Contact:  Guillermo Cabrera Walsh

The Foundation for the Study of Invasive Species (FuEDEI), formerly known as the South American Biological Control Laboratory (SABCL), is located in Hurlingham, Argentina, near Buenos Aires. The SABCL/FuEDEI plays a crucial role collecting and providing candidate biological control agents for South American weeds and pest insects for federal and state cooperators, several U.S. universities, and research collaborators worldwide since 1962. FuEDEI’ s main mission includes exploring for natural enemies of target insects and weeds in Argentina and neighboring countries and conducting host-specificity testing to determine their safety for eventual release in the U.S. In addition, complementary research that investigates the ecology, behavior, taxonomy, and genetic differences based on geographic distribution is conducted on both targets and potential agents. Performing these studies in the region of origin of the target pest serves as an efficient prescreening process that reduces the number of biocontrol agent candidates shipped. This reduces the amount of quarantine work and valuable quarantine space occupation, the expenses related to permitting processes, the risks of escapes, and the release of maladapted or wrongly identified agents to a minimum, saving in costs and hazards. On some occasions these complementary studies help us understand why an exotic organism becomes invasive, which can, in turn, lead to determining novel strategies for their management.