Technical Abstract: Growth of the corn earworm (CEW), Helicoverpa zea Boddie, a major pest of maize, Zea mays L., is inhibited by high concentrations of maysin, a C-glycosyl flavone, in maize silks. To advance understanding of the genetic control of silk maysin concentration and antibiosis to CEW, we conducted a quantitative trait locus (QTL) study in a population derived from a cross of a high-maysin (GE37) by a low-maysin (FF8) line. Both lines have phenotypically identical, positively regulating alleles at the p1 locus. We evaluated 250 (GE37 x FF8)F2:3 families for (i) restriction fragment length polymorphisms at 121 loci, (ii) silk maysin concentrations in two locations (in Georgia and Missouri), and (iii) weight of CEW larvae grown on artificial diet containing oven-dried silks. For maysin concentration in both locations, composite interval mapping revealed major QTLs in the asg20-whp1 interval of chromosome 2 and at the wx1 locus on chromosome 9. Loci with smaller effects on maysin level were detected on chromosomes 1, 6, and 8. For CEW larval weight, the largest QTL was detected in the asg20-whp1 interval of chromosome 2, and major effects were also associated with chromosomes 1 and 6. However, we found no effect on larval weight at wx1. Significant (P < 0.001) epistasis was observed for all traits. Our results suggest whp1 on chromosome 2, a gene that encodes for an enzyme early in the flavonoid pathway, and sm1, a silk-specific gene on chromosome 6, as candidate genes affecting maysin concentration and larval weight in this population.