Natural Mortality of the Lesser Cornstalk Borer (Lepidoptera: Pyralidae) in a Peanut Agroecosystem

Abstract

Lesser cornstalk borer (LCB), Elasmopalpus lignosellus (Zeller), populations were monitored for 3 yr in commercial peanut, Arachis hypogaea L., fields in an intensively cultivated area of Comanche County, Tex. Population census raw data were standardized to make LCB density estimates comparable among generations and years. Partial ecological life tables were constructed from standardized census estimates for five pivotal stages: eggs, just-hatched larvae, medium larvae, large larvae, and pupae. Mortality factors were classified as parasitism, disease, and unexplained. Identified mortality agents included an entomopoxvirus, a fungus, 13 primary parasites, and five predators. Survivorship curves implied a constant mortality rate with total generation mortality ranging from 87.1 to 96.5%. Keyfactor analysis revealed unexplained mortality was the major contributor to overall mortality, with unexplained mortality of large larvae the key mortality factor. Three methods of analyzing mortality–density relationships showed mortality was density independent, with initial egg density rather than mortality determining the resulting larval and pupal population densities.