Resistance in maize to 1st-generation European corn borer larvae,Ostrinia nubilalis(Hübner), is partly due to the antibiotic nature of 2,4-dihydroxy-7-methoxy-benzoxazin-3-one (DIMBOA). Larval bioassays (Klun et al. 1967) showed that DIMBOA and not its degradation product, MBOA, is the active agent in resistance. Normal larval development is inhibited and larval mortality increased by DIMBOA. A diallel analysis of 11 inbred maize lines by Klun et al. (1970) demonstrated highly significant correlations between DIMBOA concentration and leaf feeding resistance for inbreds and single crosses.