POPULATION-STRUCTURE IN HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE) - AN ESTIMATE OF GENE FLOW

Starch gel electrophoresis was used to evaluate the genetic population structure of the tobacco budworm, Heliothis virescens (F.). A total of 1,836 adult male moths were collected from 60 trap sites throughout Texas, Louisiana, Mississippi, Arkansas, and Georgia during a 4-wk period in 1989. An average of 30.6 (+/- 0.4) moths was electrophoretically analyzed per trap. Genotypic proportions showed no significant departures from Hardy-Weinberg expectations, suggesting random mating within populations. Population differentiation, measured by the standardized gene frequency variance, F(st), was low (F(st) = 0.002 +/- 10(-4)) but highly significant. This indicates an average local population size, Nm, of 135 (+/- 10 using a jackknife estimate), the highest value we can find reported. This figure suggests a combination of high-mobility (m) and high population size (N). Hierarchical F statistics were estimated using three levels: (1) traps within localities, (2) localities (traps within 8 km of each other) within regions, and (3) regions (localities within 80 km of each other). There was significant heterogeneity at all distance scales; however, gene frequency variance between regions and variance between localities within regions was low compared with variance within localities. These F statistics indicate that the extent of a local panmictic population has an average diameter on the order of 8 km or less.