Pathogenicity of the Entomopathogenic FungiPaecilomycesspp. andBeauveria bassianaagainst the Silverleaf Whitefly,Bemisia argentifolii

Pathogenicities of three species of entomopathogenic fungi against preimaginalBemisia argentifoliiwere measured and compared. Third-instar nymphs on excised leaves ofHibiscus rosa-sinensiswere exposed to spray applications of 14 isolates ofBeauveria bassiana,22 isolates ofPaecilomyces fumosoroseus,and five isolates ofPaecilomyces farinosus. B. bassianaandP. fumosoroseusisolates of diverse origins were highly pathogenic to the whitefly nymphs; median lethal doses of 14 of the 22P. fumosoroseusand four of the 13B. bassianaisolates ranged between 50 and 150 conidia/mm2. Five isolates ofP. farinosuswere also pathogenic; however, LC50s were relatively high, ranging between 350 and 4000 conidia/mm2. Nymphs infected with all but one isolate ofB. bassianadisplayed a pronounced red pigmentation. Postmortem hyphal growth and sporulation ofB. bassianawas relatively slow and usually confined to the region immediately surrounding the dead host. Whitefly nymphs patently infected withP. fumosoroseusandP. farinosuswere lightly pigmented yellow or orange. Postmortem hyphal growth and sporulation ofP. fumosoroseusrapidly covered the dead host and extended several millimeters onto the surrounding leaf surface. The results indicate that highly virulent strains ofP. fumosoroseusandB. bassianawith considerable whitefly control potential are widespread and numerous.