Southwestern Corn Borer Flight Well Under Way in Southern Illinois

June 11, 1999
Ron Hines, Senior Research Specialist, Dixon Springs Agricultural Center, reported that the first flight of southwestern corn borers began on May 30 in Massac and Pope counties based on pheromone trap captures. Captures of southwestern corn borer moths at the Massac County site were heaviest, with 87, 71, and 71 moths counted in a trap for June 1, 4, and 8, respectively. Ron indicated that he is keeping track of heat-unit accumulations (base 50°F) from the date of first moth capture and using guidelines from Kansas State University to track the development of southwestern corn borer larvae. This is a similar approach that we discussed in last week's Bulletin for European corn borers. After 190 heat units (base 50°F) have accumulated beyond the first flight of southwestern corn borer moths, first instars can be found, second instars at 361 heat units, third instars at 533, fourth instars at 713, fifth instars at 902, pupation at 1,153, and emergence of adults at 1,321. Ron indicated that by keeping track of heat-unit accumulations in 1998, he was able to predict within just a few days the phenological development of southwestern corn borers in southern Illinois counties.

Each female southwestern corn borer moth may lay as many as 300 to 400 eggs on the undersurface of corn leaves. Soon after hatch, larvae begin to feed on leaves; however, like European corn borers, they soon begin to tunnel into stalk tissue. The first generation of southwestern corn borer larvae typically reach full size slightly before midsummer and pupate within stalks. By early fall, second-generation larvae reach maturity and serve as the overwintering stage. Depending on summer temperatures, two to three generations may occur annually in southern Illinois, with the shortest generation period ever reported requiring only 36 days.

We look forward to more reports from Ron Hines this season.--Mike Gray

Author: Mike Gray