Factors influencing the infectivity of isolates of Paecilomyces fumosoroseus against diamondback moth, Plutella xylostella

Paecilomyces fumosoroseus isolate 1576 was isolated from an insect, but is avirulent against larvae of diamondback moth, Plutella xylostella, and seve ral other species. Isolate 1576 grew faster and produced more conidia than isolate 4461 on potato dextrose agar. Pregermination of conidia failed to i ncrease the infectivity of isolate 1576, but the procedure did increase the infectivity of isolates 3682, 4461, and 4482. Isolates 1576 and 4461 were both more infective when moisture was high during incubation of inoculated larvae. Starved PL xylostella larvae were more susceptible than fed larvae to isolate 1576 (40 and 10% mortality, respectively), but starved and fed l arvae were similar in susceptibility to isolate 4461. These results show th at isolate 1576 grows vigorously in aerial culture and is capable of infect ing stressed PL xylostella larvae. Further tests are needed to characterize its pathogenicity toward its original host or closely related species. (C) 2001 Academic Press.