Reappraising the potential of biological control against the weed Carthamus lanatus

Carthamus lanatus L. (Compositae, saffron thistle) is a major weed of worldwide distribution that originated in southern Europe. Surveys, rearings, tests of specificity, and in-depth field studies undertaken between 1990 and 1995 have considerably improved our understanding of the complex of natural enemies associated with C. lanatus in its native range. The root-feeding fly, Botanophila turcica Hennig (Dipt.: Anthomyiidae) is herewith recorded for the first time from C. lanatus; the rosette rust fungus, Puccinia sommieriana Saccardo (Basid.: Pucciniaceae) is reported for the first time from C. lanatus in Greece; the flowerhead fly, Urophora mauritanica Macquart (Dipt.: Tephritidae) is shown to concentrate its attacks on C. lanatus in the field in presence of the closely related Carthamus tinctorius L. (cultivated safflower). According to site and year the direct mortality caused by each of these three organisms to populations of C. lanatus fluctuated between 10 and 50%. In addition, each of them had a whole range of indirect effects of some importance on C. lanatus populations, all of which were also cumulative. Strong phenological (in the case of B. turcica), and practical evidence (field records, plus results of host specificity tests) are presented, and discussed which document the fact that the three phytophagous species may be considered as specifically attacking C. lanatus, but without damaging field crops of its close relative, C. tinctorius. Contrary to traditional belief, biological control may therefore be considered a promising, safe approach for reducing C. lanatus populations.