Parameters for Determination of Damage to Sweet Corn Genotypes from First and Second Generation European Corn Borer1

This research was designed 1) to determine infestation techniques and parameters best suited for assessment of relative resistance to European corn borer, (Ostrinia nubilalis Hbn.) among adapted sweet corn (Zea mays L.) hybrids, and 2) to study the interrelationships of first and second generation damage, host maturity, and environment. Four egg masses placed in the whorl and on the ear shoot were used to simulate egg laying by first and second generation corn borer adults, respectively, at Arlington, Wis. in 2 years. Husk ratings and ear tunnel counts were used to measure both first and second generation damage. Tip ratings and ear indexes were used to further evaluate second generation damage. Simple phenotypic correlations were obtained among damage parameters and maturity and Spearman's rank correlations were used to investigate the consistency of the data across years. Differences following first generation infestation in the whorl stage of development usually were not significant or consistent. Use of husk damage ratings, ear tunnel counts, and ear damage indexes following second generation infestation of ear shoots gave significant and consistent measures of hybrid differences in two markedly different seasons. First and second generation measurements of damage were not significantly related. For the hybrids included in these trials, maturity was negatively and consistently correlated with all second generation damage parameters.