Aphis nerii, the oleander or milkweed aphid, is a widespread introduced species in North America. In the northern part of their introduced range, they specialize on milkweed plants. The species is obligately parthenogenetic and can quickly reach high densities, leading to speculation that aphids may lead to a decline in milkweed quality. Parthenogenesis is also expected to lead to low spatial genetic variation, a pattern supported by previous research. However, aphids do not overwinter in northern populations, which are therefore recolonized every year. Little is known about the geography of recolonization, and this pattern might produce patterns of genetic variation that are stronger temporally than spatially. We measured aphid density and plant traits in Michigan and Pennsylvania and found a positive relationship between aphid number and leaf number. However, there was no clear relationship between monarch caterpillars (which were rare in both locations) and aphids. To test predictions of low genetic diversity, we collected individuals in both regions and sequenced them using the COI gene. We found low spatial genetic diversity, including when comparing Michigan and Pennsylvania, as predicted by the aphids’ clonal lifestyle. We did detect changes between years, as expected given the recolonization pattern of A. nerii. Together, the results present a picture of aphid ecology and genetics on a regional scale.