Using a spray-drying process to encapsulate spores of Beauveria bassiana has the potential to extend residual insecticidal activity by protecting the infective conidial spore from degradation by sunlight or other environmental factors. We previously operated a Niro Atomizer at 120o C inlet temperatures and 70-80o C outlet temperatures when processing other microbes with no adverse effect and used these conditions as a baseline for drying Beauveria. This heat drying process reduced spore germination when samples were subsequently assayed using a yeast-broth shaker-flask technique. There is considerable literature comparing incubation temperatures to maximize spore germination, but little information concerning the ability of spores to survive exposure to adverse conditions typical of this drying process. Therefore, we conducted three experiments to evaluate high temperatures on dry spores, wet spores and drying conditions. Dry spores averaged 90%, 70% and 20% germination after a 30-minutes exposure in an oven to temperatures of 50, 70 and 90o C, respectively. When suspended in water, spores did not germinate after exposure in a water bath to 50o C for 15 minutes. At 45o C, suspended spores averaged 63, 19, and 9 % germination after 15, 30, and 45-minute exposures, respectively. Reducing outlet temperatures of the spray dryer to less than 60o C did not reduce germination of the dried spores, while samples dried at outlet temperatures higher than 60o C had a reduced percentage of spore germination. The potential of using spray drying as a technique for encapsulating conidial spores is discussed.
Species 1: Deuteromycotina Hyphomycetes Beauveria bassiana
Keywords: formulations, temperature
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