Temporal and spatial patterns of allelic frequencies in cotton bollworm (Lepidoptera: Noctuidae)

Abstract

Temporal variation in allozyme frequencies at 10 allozyme loci was assessed by sampling six local populations of the cotton bollworm, Helicoverpa zea (Boddie), near cotton fields over 3 yr (1995-1997) in Leflore County, MS. Population structure over local and regional areas and changes in population structure over generations were analyzed using F-statistic estimators. There was low population differentiation at both local and regional scales, suggesting that extensive gene flow occurred within the spatial scale under investigation. Allele frequencies, heterozygosity, and the mean number of alleles per locus were stable over time and space. Measurements of population differentiation, FST, ranged from 0.0002 to 0.0072 over generations. However, there was no significant population subdivision when evaluated by bootstrapping over loci. Moreover, population differentiation as a whole and differentiation between regions was also very low, indicating that extensive gene flow occurs at both local and regional scales. Egg populations were more differentiated relative to the corresponding male moth populations, suggesting that population differentiation is greatest at egg/larval stages decreasing in adult populations due to movement. Almost all observed genetic variance was accounted for among traps within generations. Little variance was observed among generations or among years. These results further indicate that allele frequencies were stable over the duration of this study.