The entomopathogenic fungus, Beauveria bassiana is considered to be one of the few natural enemies available for use against the coffee berry borer. In an attempt to enhance the efficacy of this pathogen, a range of concentrations of 22 substances was tested in simple laboratory tests using natural sunlight or a UV light source. Unprotected B. bassiana spores were almost completely inactivated by exposure to 60 min of direct sunlight or 20 s of UV light of 302 nm wavelength. Seven of the 22 substances tested showed little or no photoprotective properties and eight of the substances appeared directly detrimental to spore germination. Of the remainder, sucrose, yeast, yeast extract, uric acid, casein, and molasses had limited photoprotective properties. The most effective substances tested were egg albumen and skimmed milk powder which could extend the persistence of B. bassiana spores by a factor of almost three. A mixture of 3% (w/v) albumen and 4% (w/v) milk powder gave the highest degree of spore protection per unit cost. Young coffee plants sprayed with this mixture did not suffer any significant phytotoxic effects. A field trial, involving two applications of spores with or without the milk and albumen mixture, failed to show that improved spore persistence resulted in increased coffee berry borer control. Very low levels of pest infestation observed in field plots together with unusual, unfavourable weather conditions may have accounted for this unexpected result.
Muñoz (Wiedemann). El rango de mortalidad que se observó fue de 9.1 a 91.9%; el tiempo letal medio de la cepa más virulenta fue de (TL 50 = 3.83 días), mientras que en la cepa con menor virulencia, el tiempo letal medio fue de (TL 50 = 17.64 días). En una segunda fase, las cepas que registraron mayor actividad biológica fueron evaluadas mediante el mismo procedimiento, en donde se registraron elevados índices de mortalidad, producción y recuperación de conidios a partir de los insectos infectados. De acuerdo con estos resultados, se discute el potencial que cinco cepas de B. bassiana tienen para ser evaluadas en condiciones de campo y determinar si pueden ser utilizadas en el control de dicha plaga. Palabras clave: Hongos entomopatógenos, B. bassiana, control microbiano, mosca del mediterráneo. (3): 609-624. ABSTRACT. Under laboratory conditions of 27 ± 2 °C, 80 ± 5% R. H. and 12:12 L:D, we performed a characterization of 16 strains of the entomopathogenic fungus Beauveria bassiana (Bals.) Vuillemin, through bioessays by immersion. The strains were isolated from different hosts and their pathogenicity was evaluated on Ceratitis capitata (Wiedemann) females. Results showed that mortality of flies ranged from 9.1 to 91.9%. Average lethal time (LT 50 ) of the most pathogenic strain was 3.8 days; while that the less pathogenic strain took 17.6 days. In a second series of experiments, the strains that registered the highest biological activity were evaluated as mentioned above. These strains showed high levels of mortality, spore production and spore recovery from the infected insects. According with these results, we discuss the potential that five strains of B. bassiana have be tested under field conditions to determinate if can be used in the control of this pest.
Muñoz
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