Epizootic Phenology of Erynia Disease of the Alfalfa Weevil, Hypera postica (Gyllenhal) (Coleoptera: Curculionidae), in Central Kentucky 1

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Abstract
The phenology of Erynia epizootic development among larval H. postica (Gyllenhal), populations [in alfalfa] in central Kentucky during 1979-1982 is described. Critical biological and physical factors governing initiation, progression and termination of the epizootic under field conditions are identified. The first incidence of Erynia disease in H. postica in central Kentucky occurred between 200 and 290 celsius day-degrees accumulated from Jan. 1st, using a base temperature of 9.degree. C. Day-degrees were used to initiate annual field sampling but did not fully explain differences in overall epizootic phenology. Although the general sigmoid shape of Erynia epizootic mortality curves were very similar in 1979-1982, certain microclimatic factors appeared to dictate the magnitude and duration of the epizootics after first incidence of disease was observed. Accumulated moisture above a base humidity threshold may serve as a key factor for explaining epizootic behavior as related to favorable and unfavorable conditions for conidial development and discharge. Natural termination of Erynia epizootics occurred when host densities fell below a critical threshold density value of 1.7 larvae/stem.