Evolutionary relationships between Deladenus nematodes parasitizing northeastern North American Sirex species

The parasitic nematode Deladenus siricidicola Kamona strain is a biological control agent of the invasive woodwasp, Sirex noctilio. Since the discovery of S. noctilio in northeastern North America in 2005, a biological control program involving D. siricidicola is under consideration. We assessed phylogenetic relationships between native Deladenus spp. in the northeastern United States to predict possible non-target effects if D. siricidicola is introduced for S. noctilio control. Parasitized Sirex spp. were collected inside and outside of the range of S. noctilio. DNA was extracted from nematodes, and three genes (CO1 mitochondrial DNA, 28S ribosomal DNA, and ITS ribosomal DNA) were sequenced and analyzed. Results show two major clades, representing the two “superspecies” proposed by Chitambar (1992). Each of the four species of Sirex has a corresponding nematode parasite. Within two Sirex noctilio we found nematodes that we hypothesize are normally associated with S. nigricornis. One individual of the native Sirex nigricornis contained Deladenus normally found in S. noctilio. We discuss nematode-host fidelity in this system and the potential for non-target impacts of a biological control program using D. siricidicola against S. noctilio.