Relation of European corn borer (Lepidoptera: Pyralidae) leaf feeding resistance and DIMBOA content in maize

European corn borer, Ostrinia nubilalis (Hubner), is a major insect pest of maize, Zea mays L., in the northern Corn Belt, which affects production through physiological yield reduction and harvest losses. Four maize inbreds (two resistant [CI31A and B75] and two susceptible [C103 and CI21E] to first-generation European corn borer along with all possible F1s [6 each] and F2s [6 each] plus the double crosses [15 each] from the F1s) were evaluated for resistance to leaf feeding by the European corn borer and 2,4-dihydrox-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) concentration in the leaf tissue. The two objectives of our study were: (1) to compare the traditional visual leaf feeding rating scale to a chemical analysis of the concentration of DIMBOA and (2) to determine the concentration and persistence of DIMBOA among these genotypes in relation to resistance. The leaf-feeding resistant inbreds, CI31A and B75, had initial ratings of 1.0 on a scale of 1-9 (1, highly resistant to 9, highly susceptible) and they had a concentration of DIMBOA of 704 and 433 micrograms/g, respectively. The susceptible inbreds, C103 and CI21E, had ratings of 7.5 and 3.8 and DIMBOA concentrations of 91 and 70 micrograms/g, respectively. The resistant ratings of the F1s and F2s were generally related to their parentage. The resistant genotypes had higher levels of DIMBOA and this trait was expressed in the various crosses in an additive manner indicating that DIMBOA concentration is genetically determined. The leaf feeding ratings became higher and DIMBOA concentrations lower as the plant matured. The correlation of leaf feeding rating and DIMBOA concentration was r = -0.40 62 d after planting, but 10 d later it dropped to r = -0.34; both are significant negative correlations. No resistance was found by the time the inbreds and crosses were flowering.