This thesis is a comprehensive treatment of the invasion genetics of two major Liposcelis pest species, Liposcelis bostrychophila Badonnel and L. decolor (Pearman), in Australian grain storage systems. Randomly amplified polymorphic DNA (RAPDs) and microsatellite DNA markers were used to investigate Liposcelis invasions in grain storage systems. The RAPD and microsatellite markers used provided insights into the genetic diversity of L. bostrychophila and L. decolor populations both in Australia and internationally, providing information integral to gaining an understanding of Liposcelis invasions in Australian grain storage systems. The thesis is divided into discrete chapters, and for each chapter an abstract is provided. Chapter 1 provides background on Liposcelis invasions in Australia in relation to the biology of Liposcelis species, the infrastructure of the Australian grain industry and the history of invasions in comparison to other invasive invertebrate species. The use of DNA and PCR technologies to investigate Liposcelis invasions are discussed and the aims and objectives of this thesis are introduced. Chapter 2 uses RAPDs to trace the geographic origin of L. bostrychophila populations in Australia from unknown geographic sources internationally. High levels of clonal genetic diversity among populations of L. bostrychophila in Australia and internationally were found. In addition, multiple introductions, from a wide range of international source populations were detected and this obscured our ability to accurately determine the geographic origin of L. bostrychophila in Australia. Given the high clonal genetic diversity found in populations of parthenogenetic L. bostrychophila in Australia, diagnostic Wolbachia PCR primers were used in Chapter 3 to investigate whether L. bostrychophila individuals from these populations were infected by Wolbachia and if infected, to investigate the strain of Wolbachia characteristic of Australian L. bostrychophila populations. Results from Chapter 3 provide the first evidence of multiple Wolbachia infection from strains A and B in Australian L. bostrychophila populations. Chapter 4 details the extensive molecular procedures undertaken to isolate microsatellite loci from Liposcelis decolor using both enrichment and nonenrichment methods. Microsatellite loci were optimised for use in PCR in single individuals following extensive troubleshooting. Troubleshooting efforts focused on elucidating the factors controlling the specificity, efficiency and sensitivity of the PCR to amplify small Liposcelis individuals known to be rich in lipids and proteins, all inhibitory to PCR. In Chapter 5 lipids and proteins were investigated from L. decolor and L. entomophila to determine total concentrations and characterize the lipids from these species. This chapter discusses whether the lipid and protein concentrations found were of a level that could be inhibitory to PCR in relation to the microsatellite techniques used in this study. From the work conducted in both Chapters 4 and 5 a troubleshooting protocol adapted for use in L. decolor was developed and implemented to determine the endogenous and exogenous parameters responsible for the function and reproducibility of PCR of microsatellite loci in L. decolor. In Chapter 6, the novel microsatellites isolated from L. decolor in Chapter 4 were used to investigate genetic structure and gene flow from Australian and international L. decolor populations. In Chapter 6 the first evidence of population differentiation, gene flow and dispersal in invasive populations of L. decolor was found. In addition, the eleven microsatellites isolated from L. decolor were cross-amplified in five other important Liposcelis pests, L. bostrychophila, L. entomophila, L. paeta, L. rufa, and L. corrodens, from which informative population genetic studies are now possible. Finally, Chapter 7 comprises the thesis synopsis, implications and future research.