Role of cuticle-degrading proteases in the virulence of Metarhizium spp. for the desert locust, Schistocerca gregaria

The production of the subtilisin proteinase, PR1, and the trypsin-like enzyme, PR2, in liquid cultures of 19 isolates of Metarhizium spp. was investigated. PR1 activity was generally observed 72 h after inoculation whilst PR2 activity was detected in most strains 48 h after inoculation. PR1 was partially purified from each isolate of Metarhizium spp. The ability of this enzyme from each isolate to degrade different types of insect cuticle was investigated. The cuticle types used were Manduca sexta pupal cuticle, adult desert locust (Schistocerca gregaria) wing cuticle, abdominal cuticle, and pharate adult locust abdominal cuticle. These cuticle types differ in their protein composition and degree of sclerotization. PR1 hydrolyzed the locust cuticle to different degrees. The data suggest a hierarchy for the susceptibility to hydrolysis in the order pharate adult abdominal > adult abdominal > wing. There was no significant correlation between the ability of the enzymes to degrade any of the cuticle types and median lethal time of the isolates against the desert locust. However, a correlation was found between the ability of enzymes to hydrolyze different locust cuticles. Such correlations were not apparent to the same extent between M. sexta cuticle and the locust cuticles. These results are discussed in terms of a possible contribution of PR1 to host specificity. (C) 1998 Academic Press.