The species of two genera in Insecta: Hemiptera: Adelgidae were investigated through the lenses of genetics, morphology, life cycle and host species. The systematics are unclear due to complex life cycles, including multigenerational polymorphism, host switching and cyclical parthenogenesis. I studied the hemlock adelgids, including the nonnative invasive hemlock woolly adelgid on the east coast of the United States, that are currently viewed as a single species. I used multivariate morphometric analyses to identify morphological differences among hemlock adelgid lineages. With principal component analyses and MANOVA, the six lineages that were used in this study were found to be significantly different from each other. The findings of this project provide evidence for taxonomic designation of different hemlock adelgid lineages, which will hopefully inform regulation of these distinct lineages, as these distinctions between the lineages of hemlock adelgids could equate to other biological differences, ex. cold tolerance, host specialization, fecundity and dispersal ability. I also investigated the relationship between species Pineus similis, Pineus abietinus through phylogeny, genetic distances, life cycle and host species. This was done through using three mitochondrial (COI, COII, cytB) and one nuclear (EF1a) gene, in Maximum Parsimony, Maximum Likelihood and Bayesian analyses, along with genetic distance measurements. The P. similis and P. abietinus on Pinus could not be separated within the Bayesian analyses, and P. similis and P. abietinus on Abies had low calculated distance measurements (2.98%) compared to the average distance between species within the genus (28.07%). These two studies emphasize the current confusion within the Adelgidae family, and the results presented in this thesis stress the importance of using components of multiple species concepts to better understand the systematics of these lineages.