Conidial Discharge and Transmission Efficiency of Neozygites floridana, an Entomopathogenic Fungus Infecting Two-Spotted Spider Mites under Laboratory Conditions

Abstract

Transmission efficiency of the entomopathogenic fungus, Neozygites floridana, was studied in laboratory populations of the two-spotted spider mite, Tetranychus urticae. Infected mites were placed in chambers with 80, 90, or 100% RH, and conidia were counted every 12 hr for 4 days. Conidial production was strongly affected by humidity, but the conidial release rate (conidia/hr) was not. The effect of host density on transmission efficiency was then tested by varying the number of susceptible hosts while holding the number of infected hosts constant and vice versa. In both cases, the proportion of infected hosts increased asymptotically in a manner closely resembling the conidial discharge curve as previously determined. Data from the latter two experiments were then combined to plot percentages of new infections against the product of susceptible and infected hosts according to a theoretical model. According to the model, this plot should be linear. Although the result showed that the linearity assumption was good at higher densities, the observations deviated significantly from linear at lower densities. We propose a nonlinear transmission term as a result of this work and suggest that similar work is needed for other entomopathogen-host relationships.