EPIZOOTIOLOGY OF THE FUNGAL PATHOGEN, ZOOPHTHORA-PHYTONOMI (ZYGOMYCETES, ENTOMOPHTHORALES) IN-FIELD POPULATIONS OF ALFALFA WEEVIL (COLEOPTERA, CURCULIONIDAE) LARVAE IN ILLINOIS

The influence of the fungal pathogen, Zoophthora phytonomi, on larvae of the alfalfa weevil, Hypera postica, was studied in three alfalfa fi elds in Illinois. Disease epizootics occurred in all three fields and disease onset was observed within a fairly narrow range of degree day accumulations. At the height of each epizootic, percentages of infecte d larvae were between 80 and 100%, and the fungus contributed to the c ollapse of the weevil population in each field. Percent parasitism by the larval parasitoids, Bathyplectes curculionis and B. anurus, was lo wer in our fields than is common in mid-season alfalfa weevil populati ons and was sometimes correlated negatively with Zoophthora phytonomi infection levels, strongly implying negative interference between the parasitoids and the pathogen. Control potential of Zoophthora phytonom i disease in alfalfa weevil larval populations is addressed.