Description of a Zoophthora Radicans (Zygomycetes: Entomophthorales) Epizootic in a Population of Empoasca Kraemeri (Homoptera: Cicadellidae) on Beans in Central Brazil

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Journal of Invertebrate Pathology



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Development of a natural epizootic of Zoophthora radicans in an Empoasca kraemeri population on beans near Goiânia, Goiás, Brazil, was monitored over a 6-week period. At the initiation of monitoring on 23 April 1985, disease prevalence in the leafhopper population was 12.8%. Over the course of the epizootic, infection of second-, third-, fourth-, and fifth-instar nymphs was similar and reached a peak of approximately 55% on 13 May, while infection of adult leafhoppers never exceeded 19%. Fungal inoculum expressed as the number of host cadavers with active (sporulating) fungus attached to the bean foliage was the variable most closely correlated to disease prevalence. Variables quantifying moisture or moisture combined with temperature (degree hours under moist conditions) were the most important abiotic predictors. A moisture variable incorporating a quantitative measure of moisture (level of wetness of a leaf wetness sensor) and a variable based only on the presence or absence of free moisture (dew) were equivalent predictors of disease prevalence. Epizootic development appeared to be inhibited when foliage was wet for less than 9 hr during the night. Infection trends in relation to fungus inoculum levels indicated an inoculum density threshold for epizootic development of approximately 0.8 leafhopper cadavers per plant.

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