PATHOGENICITY STUDIES OF A FUNGUS ASSOCIATED WITH Mononychellus tanajoa (Bondar), MITE PLAGUE OF YUCCA (Manihot

Abstract

In the cassava crop (Manihot esculenta Crantz), tetranychid mites cause considera­ble losses. Fungal epizootics that affect Mononychellustanajoa (Bondar) populations have been detected under field conditions. Healthy mites were infected under controlled conditions in the laboratory. Daily observations were made with a dissecting microscope, in order to identify disease symptoms progression. Mites were mounted on a slide and examined with a phase-contrast microscope in order to confirm the presence of a fungal pathogen and to determine its identity. Reinfection occurred when a healthy and infected mite were placed together at 70% R.H. and 20⁹-30°C. Symptoms of infection progressed from changes in body color, swelling, and sluggish movements, to death and mummification. Invasion by secondary pathogens was common. Each symptom was related to a developmental stage of the fungus, which was identified as a species of the genus Neozygites. Neozygites sp. is pathogenic to all mobile stages of M. tanajoa. Conidiogenesis was inhibited at relative humidities below 65%; however, the formation of adhesive conidia responsible for the propagation of the infection occurred only below 65% H.R. No evidence was found for pathogenicity of this fungus to phytoseiid mites