Photoprotection of beauveria bassiana: testing simple formulations for control of the coffee berry borer

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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 lowlevels of pest infestation observed in field plots together with unusual, unfavourable weather conditions may have accounted for this unexpected result. eng

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