Ovicidal and larvicidal activity of conidia and blastospores of Paecilomyces fumosoroseus (Deuteromycotina : Hyphomycetes) against Bemisia argentifolii (Homoptera : Aleyrodidae) with a description of a bioassay system allowing prolonged survival of control insects

Fungi are the only effective entomopathogens of members of the Aleyrodidae and other homopterans because of the piercing and sucking feeding strategy of these insects. The laboratory assessment of the entomopathogenic activit y of fungi often requires a prolonged period of observation. Leaf quality c art be the limiting factor in bioassays of fungi against whiteflies that re quire longer observation periods or those that require conditions that are as close to natural ones as possible. A bioassay system is described that u tilizes rooted cabbage leaves infested with the highly polyphagous whitefly , Bemisia argentifolii. Using this method, discriminating dosages of aerial conidia and blastospores of two isolates of Paecilomyces fumosoroseus (Pfr ) were bioassayed against eggs and nymphs of B.argentifolii. Low: but signi ficant, mortality (10-20%) of eggs was observed 14 days after exposure to 3 .8 x 10(4) blastospores/cm(2) for the Pfr 97 and European Biological Contro l Laboratory (EBCL) Pfr 42 isolates. Additionally, the majority of crawlers that had hatched from treated Eggs died on the surface of the leaves. Expo sure of ear ly second-instar nymphs of B. argentifolii to 3.8 x 10(3) conid ia or blastospores/cm(2) of Pfr 97 resulted in mortalities of 27 and 77% re spectively Identical dosages of conidia and blastospores of the Pfr 42 isol ate resulted in mortalities of 59 and 68% respectively. The bioassay method described enables the comparative evaluation of entomopathogenic fungi aga inst whiteflies under diverse biotic and abiotic conditions.