Epizootiology of the Fungal Pathogen, \u3ci\u3eZoophthora Phytonomi\u3c/i\u3e (Zygomycetes: Entomophthorales) in Field Populations of Alfalfa Weevil (Coleoptera: Curculionidae) Larvae in Illinois

Abstract

The influence of the fungal pathogen, Zoophthora phytonomi, on larvae of the alfalfa weevil, Hypera postica, was studied in three alfalfa fields in Illinois. Disease epizootics occurred in all three fields and disease onset was ob- served within a fairly narrow range of degree day accumulations. At the height of each epizootic, percentages of infected larvae were between 80 and 100%, and the fungus contributed to the collapse of the weevil population in each field. Percent parasitism by the larval parasitoids, Bathyplectes cur­culionis and B. anurus, was lower in our fields than is common in mid-season alfalfa weevil populations and was sometimes correlated negatively with Zoophthora phytonomi infection levels, strongly implying negative interfer- ence between the parasitoids and the pathogen. Control potential of Zooph­thora phytonomi disease in alfalfa weevil larval populations is addressed