Virulence of Beauveria bassiana Mutants for the Pecan Weevil13

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Abstract
The virulence of five mutant strains of an entomopathogenic fungus, Beauveria Bassiana (Bals) Vuill., which exhibit different capacities for pathogenicity in the corn earworm, Heliothis zea (Boddie), were established for the pecan weevil, Curculio caryae (Horn). An artificial method of infection on soil surfaces was used that approximates the naturally occurring infective process. The mutants exhibited different degrees of virulence for pecan weevil larvae; however, no positive and direct correlation to synthesis of specific extracellular enzymes (chitinases, proteinases, lipases) exists. Scanning electron microscopy revealed that penetration of the integument probably does involve extracellular enzymes of B. bassiana . Since the mutants used in this study were previously assayed for virulence against corn earworm larvae, it has been possible to compare some aspects of infection in both larval forms. The greatest difference relates to number of conidiospores required to establish an active and terminal infection. Numbers required are greater for the pecan weevil than the corn earworm, and possible reasons for this are discussed. Caprylic acid, a fatty acid found on the surface of corn earworm larvae which inhibits the germination of B. bassiana , could not be demonstrated on the surface of pecan weevil larvae.

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