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Survival of Overwintering Borers

April 12, 2002
Much has been made of the potential for insect problems after this past "mild" winter. Although mild winter weather is beneficial for the survival of some insects (e.g., bean leaf beetle, corn flea beetle), winter weather by itself has little effect on some insects. In fact, the survival of overwintering European corn borers, for example, is predicated more by the level of infection of the larvae by disease organisms.

Kevin Black, with Growmark in Bloomington, is collecting overwintering European corn borer larvae and sending them to Leellen ("Lee") Solter, insect pathologist with the Illinois Natural History Survey. Lee is checking the borers for the presence of Nosema pyrausta, a microsporidium that infects only European corn borers. Overwintering larvae infected with N. pyrausta often survive, but the infection continues through the pupal stage and into the adults. Infected females often lay fewer eggs, and fewer larvae hatch from the eggs. Infected larvae that hatch may experience delayed growth or may die. Consequently, the percentage of overwintering European corn borers infected with N. pyrausta will have an impact on the potential for corn borer problems this spring.

Kevin Black reported that 20% of the borers he collected from DeKalb County were infected with N. pyrausta. However, he has just begun examining the borers from this site, so the results are far from complete. Kevin also plans to collect borers from west-central and east-central Illinois. We'll report rates of infection in future issues of the Bulletin.

Ron Hines, senior research specialist at the Dixon Springs Agricultural Center, is more interested in survival of overwintering southwestern corn borers. Apparently, the cold snap toward the end of March had a negative impact on these borers, which do not fare well during colder winters. During the first week of April, Ron split about 20 stalks in five plot areas at the Dixon Springs Ag Center. He found only two living southwestern corn borer larvae, although 95 of the stalks had cavities below ground. He also found some dead larvae, apparently killed by the early spring freezing weather.

So, the jury is still out. We really won't know the full potential of either species until after corn has been planted (planting time also will affect the survival of these species) and moths begin to fly. That's when efforts to monitor the moth flights will pay off.--Kevin Steffey

Author: Kevin Steffey


The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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