Phylogenetic analysis of Deladenus nematodes parasitizing northeastern North American Sirex species E. Erin Morris a,⇑ , Ryan M. Kepler a , Stefan J. Long a , David W. Williams b , Ann E. Hajek a a Department of Entomology, Cornell University, Ithaca, NY 14853-2601, USA b USDA, APHIS, CPHST, Buzzards Bay, MA 02542-1308, USA article info Article history: Received 3 October 2012 Accepted 11 March 2013 Available online 28 March 2013 Keywords: Host specificity Biological control Amylostereum Woodwasp Invasive species Forest entomology abstract The parasitic nematode Deladenus siricidicola is a biological control agent of the invasive woodwasp, Sirex noctilio. Since the discovery of S. noctilio in pine forests of northeastern North America in 2005, a biolog- ical control program involving the Kamona strain of D. siricidicola has been under consideration. How- ever, North American pine forests have indigenous Sirex spp. and likely harbor a unique assemblage of associated nematodes. We assessed phylogenetic relationships among native Deladenus spp. in the north- eastern United States and the Kamona strain of D. siricidicola. We sequenced three genes (mtCO1, LSU, and ITS) from nematodes extracted from parasitized Sirex spp. collected inside and outside of the range of S. noctilio. Our analyses suggest cospeciation between four North American Sirex spp. and their asso- ciated nematode parasites. Within two S. noctilio individuals we found nematodes that we hypothesize are normally associated with Sirex nigricornis. One individual of the native S. nigricornis contained Delad- enus normally associated with S. noctilio. We discuss nematode-host fidelity in this system and the poten- tial for non-target impacts of a biological control program using D. siricidicola against S. noctilio. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Deladenus species are parasitic nematodes that attack siricid woodwasps and also some siricid parasitoids and associates (Bed- ding and Akhurst, 1978) that develop in conifers (Williams et al., 2012). Some species in the genus Deladenus (=Beddingia) have a dicyclic life history, consisting of a free-living mycophagous life cy- cle and an insect-parasitic life cycle (Chitambar, 1991). These dif- ferent strategies allow Deladenus to increase within trees as the specific wood rot fungi they eat grows, then switch to the parasitic form when siricid hosts are present, facilitating their dispersal to new trees. In the eastern United States, there are three native species of Sirex: S. nigricornis, S. cyaneus, and S. nitidus (Schiff et al., 2012). Additionally one introduced species, Sirex noctilio, was first col- lected in New York state in 2004 (Hoebeke et al., 2005). Sirex spe- cies infest trees by depositing eggs along with a symbiotic white rot fungus into the tree during oviposition. The symbiotic fungi, in the genus Amylostereum, grow throughout the wood and provide nutrition to the Sirex larvae. North American Sirex are not consid- ered serious pests as they only infest dead or dying trees (Furniss and Carolin, 1977; Madden, 1988); however, the invasive S. noctilio is capable of killing healthy trees (Spradbery, 1973). Most of what is known about Deladenus comes from in-depth studies of its use as a biological control agent against S. noctilio (Bedding and Iede, 2005). One part of the Deladenus siricidicola life cycle is spent living within the tracheids of pine trees. There, nem- atodes eat the growing hyphal tips of the white rot fungus Amylo- stereum areolatum (Basidiomycota: Russulales), the fungal symbiont of S. noctilio. Adult mycophagous nematodes mate via amphimixis, lay eggs, and develop from larvae into adults. This free-living cycle can continue indefinitely. In the presence of S. noc- tilio larvae, however, chemical cues stimulate nematode larvae to develop into preinfective adults. Preinfective adults also mate via amphimixis and the mated females use a long tubular stylet to pierce the Sirex larval cuticle and enter the host. Once inside, the nematode becomes parasitic after it sheds its outer cuticle and develops microvilli on the outside of its body, facilitating absorp- tion of nutrients from the host. This leads to rapid growth of the nematode. When the host pupates, the nematode lays eggs that will develop into mycophagous adults (Bedding, 2009). The eggs hatch and juvenile nematodes migrate to the host’s reproductive organs. Depending on the species and strain of Deladenus, juveniles can be found either within host egg shells, or around viable host eggs. In parasitized male S. noctilio, juvenile nematodes migrate to the testes, but a male S. noctilio host is a dead end for the nem- atode. When a parasitized female emerges from the tree as an adult, it mates and then oviposits on a new tree, injecting nema- todes either with or around the eggs (Bedding, 2009). 0022-2011/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jip.2013.03.003 ⇑ Corresponding author. E-mail address: eem62@cornell.edu (E. Erin Morris). Journal of Invertebrate Pathology 113 (2013) 177–183 Contents lists available at SciVerse ScienceDirect Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/jip