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Salsola tragus L. (Russian thistle, Chenopodiaceae), a weed of Central Asian origin, has two biotypes in California, type A and type B. The gall midge Desertovellum stackelbergi Mamaev (Diptera: Cecidomyiidae), which attacks S. tragus in Uzbekistan, is a candidate biological control agent for this weed in the United States. In a field test conducted in Uzbekistan with plants of the two biotypes of S. tragus from California, both biotypes were attacked by the insect, although type A was the preferred host. Accessions of S. tragus from Uzbekistan, Greece, and Ukraine were similar to the California type A when compared using RAPD and ISSR analyses, while California type B was distinct. Since both California biotypes were hosts to the gall midge, further studies on the biology and host specificity of the insect are justified. Genetic characterization of target weeds can provide information useful for the selection of natural enemies. |
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