Comparative biology of two rosette crown-feeding flies of the genus Botanophila (Dipt., Anthomyiidae) with potential for biological control of their thistle hosts

The comparative biology of two anthomyiid flies with potential for biologic al control of their host thistles, Botanophila turcica on Carthamus lanatus and Botanophila spinosa on Onopordum acanthium, was studied using field su rveys and collections, and by rearing collected eggs and larvae in the labo ratory in southern France. The thistle hosts are significant weeds outside their native range, particularly in Australia. Both flies attack the rosett e meristems of their hosts prior to flowering. Larval stages are described together with natural attack rates (21-33% of field plants) and the mortali ty of field-collected larvae reared in the laboratory. A successful rearing protocol for these flies is also described. The results of preliminary hos t-specificity tests showed that both species are highly specific, being res tricted to their host genus in the tests conducted. Furthermore, Botanophil a turcica could not complete development on safflower (a congener of its na tural host) under natural conditions. Botanophila turcica had an adult acti vity period that lasted 6 months from late autumn and laid fewer eggs per h ost plant than B. spinosa, which was active for 2 to 3 months in spring. On ly one parasitoid was observed, an endoparasitic eucoilid, Trybliographa sp ., which attacked both fly species, causing 18-23% mortality.