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 biological control of their host thistles, Botanophila turcica on Carthamus lanatus and Botanophila spinosa on Onopordum acanthium , was studied using field surveys and collections, and by rearing collected eggs and larvae in the laboratory in southern France. The thistle hosts are significant weeds outside their native range, particularly in Australia. Both flies attack the rosette meristems of their hosts prior to flowering. Larval stages are described together with natural attack rates (21–33% of field plants) and the mortality of field-collected larvae reared in the laboratory. A successful rearing protocol for these flies is also described. The results of preliminary host-specificity tests showed that both species are highly specific, being restricted to their host genus in the tests conducted. Furthermore, Botanophila turcica could not complete development on safflower (a congener of its natural host) under natural conditions. Botanophila turcica had an adult activity period that lasted 6 months from late autumn and laid fewer eggs per host plant than B. spinosa , which was active for 2 to 3 months in spring. Only one parasitoid was observed, an endoparasitic eucoilid, Trybliographa sp., which attacked both fly species, causing 18–23% mortality.