Discovery of a potentially destructive non-native woodwasp, Sirex noctilio F. (Hymenoptera: Siricidae), in pine forests of eastern North America has elicited interest in appropriate management options. A parasitic nematode, Deladenus siricidicola Bedding (Tylenchida: Neotylenchidae), was introduced as a biological control agent in the Southern Hemisphere where it has been successful in some areas and unsuccessful in others. The North American congener (D. proximus Bedding) parasitizes native Sirex woodwasps and has potential as a biological control agent of S. noctilio due to its ability to utilize the invasive woodwasp as a novel host. However, basic biology and ecology of these native nematodes are largely unknown. Sirex nigricornis females were collected from three geographic locations in Arkansas in 2009 and 2010, dissected, and examined for the presence of D. proximus. Nematodes were found within S. nigricornis collected from all locations and years. Parasitism negatively affected woodwasp body size. We found high variation in percent of eggs infected with nematodes during both years of trapping. Research is needed to investigate potential mechanisms behind this variation of parasitism.