Effects of corn host plant resistance on the southwestern corn borer

The southwestern corn borer (Diatraea grandiosella Dyar) is a serious pest of corn (Zea mays L.) in the southern United States. It completes two to three generations per year depending upon latitude. The first generation attacks whorl stage corn. Corn germplasm lines with conventional genetic leaf-feeding resistance to this pest and other lepidopterans have been released to the public by USDA-ARS scientists. An initial objective of the present study is to provide baseline biological data for southwestern corn borers grown on two leaf-feeding resistant hybrids and one susceptible hybrid. Plants were infested with neonate larvae after reaching the V8-V9 leaf stage. Data on survival, growth and development of southwestern corn borers on these hybrids were taken at specified time intervals throughout the entire generation period by destructive sampling of plants. Extent of leaf feeding damage and stalk tunneling were also taken for each hybrid. A second objective involved examining the peritrophic membrane of larvae reared under field and laboratory conditions on these three hybrids to determine if the resistant factors adversely affected the peritrophic membrane. Scanning electron microscopy was used to examine the peritrophic membrane for abnormalities (holes/tears).; Results of this study clearly demonstrated that the resistant hybrids supported fewer numbers of larvae, larval development was slower, and overall less plant damage was sustained. Observation of the peritrophic membranes from larvae feeding on the resistant and susceptible hybrids failed to reveal any significant differences when the degree of damage to the membrane was quantified.