POPULATION-DYNAMICS OF THE ALFALFA WEEVIL (COLEOPTERA, CURCULIONIDAE)IN CENTRAL AND SOUTHERN IOWA

Eight life tables were constructed for the alfalfa weevil, Hypera post ica (Gyllenhal), from populations at four Iowa sites in 1991 and 1992. A fungal pathogen, Zoophthora phytonomi Arthur, was the key factor re gulating within-generation population trends in 1991. The disease caus ed high mortality of alfalfa weevil during the third and fourth stadia . Other unknown mortality factors were important in regulating populat ion densities in 1992. These undetermined mortality factors may have i ncluded failure of early instars to establish on alfalfa plants and pr edation of all instars. Two larval parasitoids, Bathyplectes curculion is (Thomson) and Bathyplectes anurus (Thomson) caused a relatively sma ll percentage of mortality during both 1991 and 1992.