Variation in sterilization and genetic diversity of Deladenus proximus Bedding, a nematode of the native, pine-inhabiting woodwasp, Sirex nigricornis F. (Hymenoptera: Siricidae)

The native pine-inhabiting woodwasp, Sirex nigricornis F. (Hymenoptera: Siricidae) is not known to be a pest in its native range of the eastern U.S. and Canada.  However, the recently introduced woodwasp, S. noctilio, has been known to cause widespread mortality to commercial pine plantations in areas of previous introduction.  Its consistent spread throughout the U.S. and Canada suggests that it will eventually reach the multi-billion dollar pine timber industry of the Southeast.  The nematode Deladenus siricidicola Bedding has been successfully used as a biological control agent of S. noctilio in the past.  Native nematodes in the same genus naturally sterilize native woodwasps and have been found inhabiting the eggs and mycangia of S. noctilio in the Northeast.  Our objectives of this study are to examine the variation in sterilization of native woodwasps by these nematodes and to evaluate the genetic diversity of those nematodes in relation to their percent sterilization.  After examination of eggs and mycangia for the presence of nematodes, we performed PCR using a primer set previously designed to amplify the ITS region of D. siricidicola.  Percent of sterilized woodwasp eggs in nematode-positive females ranged from 50-100%.  All females which had nematode-infected eggs also had infected mycangia.  Preliminary results suggest multiple species of Deladenus in the southeastern United States which may be related to the proportion of wood wasp eggs sterilized. Live nematodes will be obtained from adult female wood wasps and reared out to adulthood for morphological identification to make our molecular identification more robust.