The role of immigrant inviability in mediating the genetic differentiation between populations of Aphidoidea species associated with pecan and water hickory trees

Host-associated differentiation (HAD) is a form of ecologically mediated speciation by which two or more parasite populations (e.g., insect herbivores) of the same species become genetically distinct due to their associations with different host species (e.g., plants). HAD has been proposed as a possible explanation for the vast species diversity observed in herbivorous insects. The factors involved in the development and/or maintenance of HAD, though, are not fully understood. In general, differential selection pressures experienced by insect species on different host plants seem to explain HAD. However, the specific mechanisms involved may vary in different insect and plant systems. One such mechanism is immigrant inviability, a process in which individuals migrating to a novel host species have reduced fitness compared to individuals that remain with their natal host species. In order to learn whether immigrant inviability is related to the development and/or maintenance of HAD, it is necessary to study several species within a community context in the same host species pair in order to correlate patterns of HAD with the patterns in ecological components that may be involved in the formation and maintenance of HAD. Host-associated differentiation has been studied in a few Aphidoidea species that occur on pecan and water hickory trees. In this system some species show strong (3 species), weak (1 species) and no HAD (2 species); immigrant inviability has been tested and found in one aphid species. I expand upon this research by testing other pecan- and water hickory-associated Aphidoidea species for immigrant inviability.