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

The entomopathogenic fungus, Beauveria bassiana is considered to be one of the few natural enemies available for use against the coffee berry borer. I n an attempt to enhance the efficacy of this pathogen, a range of concentra tions of 22 substances was tested in simple laboratory tests using natural sunlight or a UV light source. Unprotected B. bassiana spores were almost c ompletely inactivated by exposure to 60 min of direct sunlight or 20 s of U V light of 302 nm wavelength. Seven of the 22 substances tested showed litt le or no photoprotective properties and eight of the substances appeared di rectly 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 skimm ed 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 p owder gave the highest degree of spore protection per unit cost. Young coff ee plants sprayed with this mixture did not suffer any significant phytotox ic effects. A field trial, involving two applications of spores with or wit hout the milk and albumen mixture, failed to show that improved spore persi stence resulted in increased coffee berry borer control. Very low levels of pest infestation observed in field plots together with unusual, unfavourab le weather conditions may have accounted for this unexpected result.