Epidemiology of Nomuraea rileyi (Fungi: Deuteromycotina) in Plathypena scabra (Lepidoptera: Noctuidae) Populations from Iowa Soybeans

Abstract

Data from a 10-year study were analyzed to understand the epidemiology of Nomuraea rileyi (Farlow) Samson in green cloverworm (GCW), Plathypena scabra (F.), populations in Iowa. Larvae were collected by sweeping in soybean fields each year from 1971 through 1980 and were maintained in the laboratory until completion of development or death. Six endemic and 4 outbreak GCW population types were identified from the 10 collection years. N. rileyi was a major agent of GCW mortality, especially during the second GCW generation of outbreak years. The seasonal increase in percentage N. rileyi -caused mortality in outbreak populations is described as a function of the number of days after the date of initial detection of infected larvae. In all years, the mortality rate of the second GCW generation from N. rileyi infection is significantly dependent on the size of the first GCW generation. The date of first prominent (2%) N. rileyi -caused mortality is significantly explained by the accumulated larva-days and accumulated precipitation from 1 June. These results support and supplement existing explanations of GCW population dynamics in Iowa by providing quantitative expressions of N. rileyi epidemiology.