Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/8/2005
Publication Date: 7/29/2006
Citation: Lewis, L.C., Sumerford, D.V., Bing, L.A., Gunnarson, R.D. 2006. Dynamics of Nosema pyrausta in natural populations of the European corn borer, Ostrinia nubilalis: A six-year study. Biocontrol. 51(5):627-642. Interpretive Summary: The European corn borer, a serious pest of corn in the United States, is controlled by many naturally occurring events including a one-celled organism Nosema pyrausta. Nosema is passed from adult female through the egg to offspring. It reduces the number of eggs laid and the number that hatch. Researchers conducted an extensive study for six years to determine the percentage of adults, eggs, larvae, and pupae infected with Nosema. It was found that all life stages were infected, and Nosema was successfully passed from one form to the next. There were no environmental factors, i.e., temperature, moisture, identified that influenced Nosema. This research benefits entomologists in developing management programs.
Technical Abstract: Nosema pyrausta (Paillot) is an obligatory intracellular parasite of the European corn borer, Ostrinia nubilalis (Hubner) (Lepidoptera: Crambidae). This pathogen is maintained in natural populations of O. nubilalis by both horizontal and vertical transmission. The impact of N. pyrausta on fecundity of adults and survival of larvae has been well documented in laboratory and field research. In an extensive study covering a six-year period at one site, we described the effect of N. pyrausta within O. nubilalis populations in a continuous corn following corn ecosystem. We documented the presence of the pathogen through all life stages of O. nubilalis (egg, larva, pupa, adult) by collecting throughout the crop season and examining each insect stage in the laboratory for the frequency of infection with N. pyrausta. The number of insects collected in each life stage was correlated with the percentage of the population infected with N. pyrausta. The percentage of infection with N. pyrausta and magnitude of the O. nubilalis population fluctuated throughout generations 1 and 2. Both horizontal and vertical transmission played a role in maintaining N. pyrausta in the population in both cycles. There were strong correlations between percentage adults with N. pyrausta and percentage larvae with N. pyrausta, and between percentage eggs with N. pyrausta and percentage larvae with N. pyrausta. There was a weak correlation between percentage adults with N. pyrausta and percentage eggs with N. pyrausta. The percentage of insects infected with N. pyrausta was always lowest in the egg.