Date of Award
Master of Science
Jimenez, F. Agustin
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.
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