Breeding structure of a colonising species: Aedes albopictus (Skuse) in the United States.

Allelic and genotypic frequencies were monitored at seven enzymatic loci in newly established Aedes albopictus (Skuse) populations in the United States. Populations were sampled within the cities of New Orleans, Louisiana, Houston, Texas, three counties surrounding Houston, Memphis, Tennessee, Jacksonville, Florida, and Evansville and Indianapolis, Indiana. Unique alleles and relatively high levels of heterozygosity were detected in New Orleans, Houston, surrounding counties and Indianapolis suggesting relatively large and independent introductions in these cities. No unique alleles and low heterozygosities were detected in Memphis, Evansville and Jacksonville suggesting that a population bottleneck may have accompanied the founding of these populations. The bottleneck may have resulted from a small number of founding individuals or may have been generated through repeated control efforts. Genetic distance estimates indicated that Houston, New Orleans and Indianapolis were genetically similar. Evansville and Memphis were also found to be similar. Significant differentiation of allele frequencies existed among and within cities. Variance in allele frequencies among all samples was partitioned into the variance among cities and among locations within cities. Most of the variance was attributable to local differentiation. The most parsimonious explanation of this result is that much genetic drift accompanied the establishment of local populations in cities and that there has been little subsequent gene flow. Analysis of genotypic frequencies detected a slight but consistent excess of homozygotes suggesting inbreeding.