Natural coprevalence of Strongwellsea castrans, Cystosporogenes deliaradicae, and Bacillus thuringiensis in the host, Delia radicum

Adult cabbage root flies (Delia radicum) from three Danish localities were diagnosed microscopically for the natural prevalence of Strongwellsea castr ans, Cystosporogenes deliaradicae, and Bacillus thuringiensis. C. deliaradi cae was significantly coprevalent with S. castrans. B. thuringiensis sporan gia were diagnosed in the hemolymph in two D. radicum which were also infec ted with S. castrans and proved to belong to serovar aizawai and serovar ba learica. The biological characterization of S. castrans proved that at 17.5 degrees C dies developed an abdominal hole 7.9 days (mean) after infection and that 5.7 days (mean) passed from the emergence of the hole to the deat h of the infected host. No mortality effect among D. radicum subjected to B . thuringiensis serovar aizawai, balearica, and kurstaki isolates was detec ted. RAPD with DNA proved that six B. thuringiensis serovar balearica isola tes (all from the same fly) were indistinguisable. This indicates that prol iferation of B. thuringiensis in the abdomen of an S. castrans-infected D. radicum may be due to just one genotype. The profiles of one isolated aizaw ai strain did not correspond to the profiles of other serovar aizawai strai ns used for comparison. The biological significance of the interaction betw een the involved pathogens is discussed. (C) 2000 Academic Press.