Technical Abstract: Seven polymorphic microsatellite markers were used to analyze Helicoverpa zea (Boddie) populations from various host plants in four different locations in the southern United States. Linear distance between collection sites ranged from approximately 150 to 900 km. Mean number of alleles per locus ranged from 2.286 ± 0.488 to 2.571 ± 0.787 and mean observed and expected heterozygosities ranged from 0.364 ± 0.101 to 0.459 ± 0.168 and 0.413 ± 0.130 to 0.447 ± 0.088, respectively. Chi-square goodness of fit tests for deviation from Hardy-Weinberg equilibrium were not significant. Inbreeding coefficients, FIS, were highly variable among the seven loci with a bootstrap generated overall value of -0.104 ± 0.178 across all loci and populations. Overall population differentiation estimates, represented by FST, were essentially zero. In the analysis of variance performed by grouping genotypes into various geographical combinations, variation within individuals accounted for over 91% of the total variation while no significant variation was detected between groups, among populations within groups, or among individuals within populations. The results indicated that extensive gene flow occurred between geographically distant H. zea populations, and the populations studied did not show any signs of differentiation based on the geographical location. Although there are no other microsatellite based population studies for comparison, the results of the present study are congruent with the results of allozyme analyses on this species.