Effect of Formulation on the Viability of Metarhizium Anisopliae Conidia

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Journal of Invertebrate Pathology





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Fourteen oils, including mineral oil, cod liver oil, and 12 vegetable oils, were highly detrimental to Metarhizium anisopliae conidial viability after 2 months storage at 26° and 19°C. Most oilconidial suspensions (8 of 14) also lost conidial viability more rapidly than unformulated conidia at 4°C. The viscosity of oils was not related to the rapid loss of conidial viability in these formations. Other liquid vehicles, including petroleum-based oils, organic acids, and water, with or without a surfactant, were also highly lethal to conidia after 4 months of storage. In contrast to liquid formulations, high conidial viabilities were retained on most dry formulations, including four different granular carriers and 12 different dust diluents, over a 1-year period at 4°C. At 20°C, however, conidial viabilities declined to below 50% with most dry diluents. Dust diluents were generally more compatable with conidia than granular carriers. Unformulated conidia mixed with two desiccants lost germination capacity sooner than conidia exposed to, but separated from, anhydrous CaCl2. On the other hand, conidia in a dust formulation mixed with kaolinite clay and powdered silica gel survived longer than unformulated conidia either mixed with or separated from the desiccant. This study confirms the need for careful assessment of the compatibility of formulation components with conidia prior to their use in formulations.

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