Pathogenicity of the entomopathogenic fungi Paecilomyces spp. and Beauveria bassiana against the silverleaf whitefly, Bemisia argentifolii

Pathogenicities of three species of entomopathogenic fungi against preimaginal Bemisia argentifolii were measured and compared. Third-instar nymphs on excised leaves of Hibiscus rosa-sinensis were exposed to spray applications of 14 isolates of Beauveria bassiana, 22 isolates of Paecilomyces fumosoroseus, and five isolates of Paecilomyces farinosus. B. bassiana and P. fumosoroseus isolates of diverse origins were highly pathogenic to the whitefly nymphs; median lethal doses of 14 of the 22 P. fumosoroseus and four of the 13 B. bassiana isolates ranged between 50 and 150 conidia/mm(2). Five isolates of P. farinosus were also pathogenic; however, LC(50)s were relatively high, ranging between 350 and 4000 conidia/mm(2). Nymphs infected with all but one isolate of B. bassiana displayed a pronounced red pigmentation. Postmortem hyphal growth and sporulation of B. bassiana was relatively slow and usually confined to the region immediately surrounding the dead host. Whitefly nymphs patently infected with P. fumosoroseus and P. farinosus were lightly pigmented yellow or orange. Postmortem hyphal growth and sporulation of P. fumosoroseus rapidly covered the dead host and extended several millimeters onto the surrounding leaf surface. The results indicate that highly virulent strains of P. fumosoroseus and B. bassiana with considerable whitefly control potential are widespread and numerous. (C) 1998 Academic Press.