Submitted to: World Journal of Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 5, 1996
Publication Date: N/A
Interpretive Summary: Whiteflies have become a severe pest in the Southern United States since 1986, causing $200-500 million losses in vegetables and cotton annually. Furthermore, whiteflies develop rapid resistance to chemical insecticides. The fungus Paecilomyces fumosoroseus has been shown to infest and kill whiteflies in the field. Development of this bioinsecticide depends on a high production of fungal spores that tolerate drying and storage before field application. Current experiments have focused on the impact of culture media on spore tolerance to drying. Selection of these media requires a fast and reliable spore drying method. In this study, we investigated three methods of drying spores: silica gel, sand, or diatomaceous earth at controlled humidity. Among the three methods, the silica gel drying method was selected because changes in spore survival can be monitored and because the test was rapid. Using this method, numerous media can be screened for their ability to produce spores capable of tolerating drying. Identification of production processes which yield stable microbial biocontrol agents will enable "environmentally friendly" biocontol agents to become commercial products.
Technical Abstract: Selecting methods for producing desiccation tolerant spores of the potential fungal bioinsecticide Paecilomyces fumosoroseus (Pfr) requires a rapid, reliable drying method. Three air-drying methods were tested: Pfr spores mixed with silica gel, sand, or diatomaceous earth. Pfr silica gel and Pfr sand drying methods were performed without humidity control, and the Pfr-diatomaceous earth method was performed with controlled humidity. Spore survival after drying was 19% (coef. of variation range: 32 to 45), 82% (coef. of variation range: 26 to 43), and 2% (coeff. of variation: 32% to 50%) with silica gel, sand and diatomaceous earth, respectively. Variation observed within each method was similar. Among the three methods, the silica gel drying method was selected because of moderate spore survival (19%) and because the test was rapid.