Salsola kali

<br>The gall midge Desertovellum stackelbergi (Diptera: Cecidomyiidae), which attacks S. tragus in Uzbekistan, was identified as a candidate biological control agent for S. tragus in the USA (Sobhian et al., 2003). In a field test conducted in Uzbekistan, Californian S. tragus biotype A, similar to accessions from Uzbekistan, Greece and Ukraine, was the referred host, whereas Californian biotype B was distinct, though also attacked. Since both California biotypes were hosts to the gall midge, further studies on the biology and host specificity of the insect were considered justified (Sobhian et al., 2003).<br>The obligate biotrophic rust fungus Uromyces salsolae is a candidate biological control agent of S. tragus. Host range tests were conducted in quarantine and only species in the genus Salsola were susceptible to the fungus (Berner et al., 2009).<br>The eriophyid mite Aceria salsolae was also evaluated as a prospective classical biological control agent of invasive alien tumbleweeds, including Salsola tragus, S. collina, S. paulsenii and S. australis, in North America (Smith et al., 2009). S. tragus was heavily infested by A. salsolae and plant size was negatively correlated to the level of infestation. Although S. kali plants were also infested, plant size did not appear to be affected by the mites. Other nontarget plants were not as suitable for the mite in the field as in previous laboratory experiments, and it was concluded that there would be no significant risk to using A. salsolae as a biological agent in North America (Smith et al., 2009).<br>Two species of coleophorid moths are also reported to have been introduced to control S. tragus in western USA, where they became widely established;however, they were heavily attacked by predators and parasitoids and have not reduced S. tragus populations.<br>Cosmobaris scolopacea is a weevil distributed in Eurasia and North America, generally associated with the Chenopodiaceae family of flowering plants. The larvae feed and pupate within stems. Preliminary host range testing in Italy confirmed the presence of a highly divergent Sicilian lineage of C. scolopacea that was reared only on S. kali, indicating that this type requires further testing as a biological control agent (Cristofaro et al., 2011).<br>Colletotrichum gloeosporioides f. sp. salsolae is a facultative parasitic fungus being evaluated as a classical biological control agent of S. tragus in initial host range determination tests (Berner et al., 2012). Greenhouse tests showed that it is specific to Salsola spp., and that pathogen and inoculation procedures offer a low-cost solution to S. tragus infestations (Berner et al., 2014).<br>Despite the large number of identified potential biological control agents and host specificity testing, there appear to be few records of actual releases or more widespread field testing of the above.