AN ENTOMOGENOUS FUNGUS, NEOZYGITES FLORIDANA WEISER AND MUMA; MITE AERIAL DISPERSAL; AND ENVIRONMENTAL CONDITIONS AS FACTORS IN POPULATION DECLINES OF THE TWOSPOTTED SPIDER MITE, TETRANYCHUS URTICAE KOCH (ENTOMOPHTHORALES, EPIZOOTICS)

In predator-suppressed field plots in eastern North Carolina, populations of the twospotted spider mite, Tetranychus urticae Koch, on field corn declined in association with mite aerial dispersal, or epizootics of the entomogenous fungus, Neozygites floridana. The relative importance of these two factors varied from year to year depending upon environmental conditions. When moist weather conditions induced epizootics of N. floridana before corn plants became heavily infested with mites, the pathogen appeared to be the major factor causing mite population declines. When dry weather conditions allowed mite populations to expand unchecked until corn plants became entirely infested, mite aerial dispersal was the major factor associated with mite population declines.; In laboratory, greenhouse, and field studies, nightly periods (>8 hr/day) of approximately 100% RH with temperatures from 15 to 21(DEGREES)C were found to be highly conducive to the development of epizootics of N. floridana in populations of spider mites.; Adult females, deutonymphs and protonymphs of T.urticae were discovered to manifest an active aerial dispersal behavior in response to wind and light. This behavior was manifested by mites collected from deteriorating host plants and by mites allowed to desiccate under laboratory conditions. Multiple regression analysis of field data indicated that mite aerial dispersal was positively correlated with the percent corn leaf area infested with mites and with mite population density. Aerial dispersal was negatively correlated to periods of high RH and fungal epizootics.