The pathogenicity of Serratia strains to Lucilia sericata (Diptera: Calliphoridae)

Adult blowflies, Lucilia sericata, were tested for susceptibility to 11 strains of Serratia marcescens, 2 strains of Serratia liquefaciens, and 1 strain of Serratia entomophila in a series of 14 laboratory bioassays. Most bacterial strains were initially isolated from insects. S. marcescens strains were characterized to biotype level. Most strains conformed to biotype A2a, the group most commonly associated with insects. Flies were held individually in small tubes and fed bacterial suspensions containing approximately 1 x 10(9) bacteria ml(-1) in a single 24-hr feeding period. For the remainder of the experiment, flies were fed sucrose solution. Eight of the S. marcescens strains caused significant mortality (P < 0.05-0.001), measured as death rate compared to untreated flies. Four strains had no effect on the flies (P > 0.05). The time taken to reach 50% mortality (LT(50)) ranged from 6.38 to 7.49 days for the pathogenic S. marcescens strains compared to LT(50)s of 8.81-11.73 days for the nonpathogenic strains, which did not differ significantly from the untreated control flies (LT(50) of 10.38 days). After 7 days, mortality caused by the pathogenic strains ranged from 21 to 45% of treated insects. One strain of S. liquefaciens also caused significant mortality while the other was nonpathogenic. No mortality resulted from treatment of flies with S. entomophila. (C) 1996 Academic Press, Inc.