Technical Abstract: The Bemisia tabaci cryptic species complex of whiteflies contains two species, MEAM1 and MED, that are highly invasive in supportive climates the world over. In the U.S. MEAM1 occurs both in the field and in the greenhouse but MED is only found in the greenhouse. In order to make inferences about the population structure of both species, and the origin and recent spread of MED within the U.S., 987 MEAM1 whiteflies and 340 MED whiteflies were genotyped at six and seven microsatellite loci respectively for population genetic analyses. Major results of the study are 1) MED exhibits more population structure and genetic differentiation than MEAM1, 2) nuclear microsatellite markers exhibit a high degree of concordance with mitochondrial markers recovering a major east/west phylogeographic break within MED, 3) both eastern and western MED are found throughout the continental U.S. and eastern MED is present in Hawaii, and 4) MEAM1 contains two greenhouse U.S. populations significantly differentiated from other U.S. MEAM1. The results suggest that MED was introduced into the U.S. on at least three occasions and rapidly spread throughout the U.S., showing no discernable differentiation across 7,000 kilometers. The results further suggest that there is an enhanced role of the protected agricultural environment in promoting genetic differentiation in both invasive Bemisia tabaci cryptic species.