Deladenus proximus (Neotylenchidae) is a nematode associated with pine trees and woodwasps, Sirex nigricornis (Hymenoptera). Previous to this study, little was known about the geographic distribution and variability of D. proximus. Herein I present information about their life cycle, pathogenicity, and variability. The life cycle is similar to that of other species of Deladenus in that it includes mycetophagous and entomopathogenic stages. Fertilized female nematodes penetrate siricid larvae and grow in the body cavity releasing thousands of larvae. These larvae invade the gonads, mycangia (sacs containing symbiotic fungus) and eggs upon metamorphosis of the host. Females oviposit infected eggs and spores of fungus (Amylostereum chailletii) into stressed trees, where nematodes mature and feed on the fungus, completing the life cycle. From 2009 to 2012 a total of 1,574 woodwasps were collected from Arkansas, Illinois, Louisiana, and South Carolina. Woodwasps were dissected and live nematodes were reared on cultures of A. chailletii and examined upon maturation. Reared nematodes were compared against type specimens of D. ipini and published descriptions of D. proximus. My study indicates prevalence varied across localities but every infected female wasp was sterilized, as indicated by presence of nematodes in the eggs. In addition I compared diagnostic characteristics of adult nematodes from each locality and found no significant difference in their size and structures. The nuclear loci 18S, 5.8S and ITS1 and 2 and the mitochondrial locus cox1 were amplified from each nematode. Nuclear DNA was invariable from all 4 locations and had 99% identity to the invasive species Deladenus siricidicola. Analysis of mitochondrial DNA showed more variability so these data were used to evaluate genetic structure across localities. Analysis of the cox1 data revealed 19 haplotypes and the absence of any geographic clusters or subpopulations. The lack of geographic structure may be due to the fact that each female wasp is infected with only one adult female nematode and therefore larvae within a wasp are siblings. With a generation time of 2 weeks these nematodes can have 20 generations without immigration or emigration, suggesting these nematodes are inbred. The pattern of transmission of this nematode and pathogenicity is similar to that of Deladenus siricidicola, which is used as a biocontrol against the invasive species Sirex noctilio. Experimental infections of Deladenus proximus in Sirex noctilio are recommended to test their viability as a biocontrol agent.

Both insect parasitic/entomopathogenic nematodes and plant parasitic nematodes are of great economic importance. Insect parasitic/entomopathogenic nematodes provide an environmentally safe and effective method to control numerous insect pests worldwide. Alternatively, plant parasitic nematodes cause billions of dollars in crop loss worldwide. Because of these impacts, it is important to understand how these nematodes evolve, and, in the case of entomopathogenic nematodes, how their bacterial symbionts evolve. This dissertation contains six chapters. Chapter one is a review of DNA markers and their use in the phylogenetic systematics of entomopathogenic and insect-parasitic nematodes as well as a review of phylogenetic, co-phylogenetic, and population genetic methodologies. Chapter two characterizes positive destabilizing selection on the luxA gene of bioluminescent bacteria. Our data suggests that bacterial ecology and environmental osmolarity are likely driving the evolution of the luxA gene in bioluminescent bacteria. Chapter 3 examines relationships among bacteria within the genus Photorhabdus. Our analyses produced the most robust phylogenetic hypothesis to date for the genus Photorhabdus. Additionally, we show that glnA is particularly useful in resolving specific and intra-specific relationships poorly resolved in other studies. We conclude that P. asymbiotica is the sister group to P. luminescens and that the new strains HIT and JUN should be given a new group designation within P. asymbiotica. Chapter 4 characterizes the morphology of the head and feeding apparatus of fungal feeding and insect infective female morphs of the nematode Deladenus siricidicola using scanning electron microscopy. Results showed dramatic differences in head, face, and stylet morphology between the two D. siricidicola female morphs that were not detected in previous studies using only light microscopy. Chapter five utilizes comparative transciptomics to identify putative plant and insect parasitism genes in the nematode Deladenus siricidicola. Results from this study provide the first transcriptomic characterization for the nematode Deladenus siricidicola and for an insect parasitic member of the nematode infraorder Tylenchomorpha. Additionally, numerous plant parasitism gene homologues were discovered in both D. siricidicola libraries suggesting that this nematode has co-opted these plant parasitism genes for other functions. Chapter six utilizes a phylogenomic approach to estimate the phylogeny of the nematode infraorder Tylenchomorpha.