Green Cloverworm (Lepidoptera: Noctuidae) Population Dynamics: Pupal Life Table Studies in Iowa Soybeans1

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Abstract
Six partial life tables were prepared for pupal green cloverworms (GCW), Plathypena scabra (F.), during 1979 and 1980. Pupal dynamics were characterized by large first-generation densities that declined below detectable levels during generation 2 in 1979, and by small first-generation densities that expanded sevenfold during generation 2 in 1980. The 1979 and 1980 density patterns are characteristic of outbreak and endemic GCW population configurations, respectively. Survivorship during generation 1 was fourfold greater under endemic population levels than under outbreak levels. Pupae were parasitized by 11 primary species. Parasitization represented less than 18% of total 1979 pupal mortality but accounted for 60% of total 1980 mortality. Infections caused by a microsporidian and by the entomogenous fungus Nomuraea rileyi (Farlow) Samson accounted for a small portion of total mortality, as did deaths attributed to nonviability. Predation was 2.5 times greater under outbreak levels than under endemic levels during generation 1. A modified key factor analysis indicated that no single mortality component was correlated with changes in total pupal mortality. Regression analyses indicated that Vulgichneumon brevicinctor (Say) (Hymenoptera: Ichneumonidae) acted in a delayed density dependent manner and that total pupal mortality was density dependent.