Effects of native nematodes on size and fecundity of native woodwasps in southeastern pine forests

Sirex nigricornis F. is a native woodwasp in eastern North America that inhabits dead and dying pine trees during its univoltine development. Sirex noctilio is native to Eurasia and North Africa and was discovered in the northeastern United States in 2004 after more than a century of accidental introductions across the Southern Hemisphere.  Since its introduction, it has spread to seven states and much of southern Ontario.  The native nematode, Deladenus proximus Bedding (Tylenchida: Neotylenchidae), directly and indirectly affects S. nigricornis and has been found parasitizing S. noctilio in the northeastern U.S., implicating it as a potential control agent for S. noctilio in North America.  Additionally, D. siricidocla, the associated nematode of the non-native woodwasp, has been detected in North America in both S. noctilio and S. nigricornis and both nematode species are able to grow and reproduce on multiple species of the Sirex symbiotic fungus, Amylostereum (Basidiomycota: Russalules).  The relationship among these organisms is extremely complicated and still relatively unknown.  Our objectives were to 1) examine the effects of nematode infection on S. nigricornis female body size and fecundity, 2) confirm the identity of native nematodes in southeastern woodwasps using molecular techniques, and 3) evaluate the potential for use of native nematodes in biological control of S. noctilio in North America.  Over 500 native wood wasps were collected in the fall of 2012, 2013, and 2014, measured and dissected.  Nematodes were found in multiple areas of the female body including the eggs, mycangia, and haemocoel.  Proportion of eggs sterilized within infected females ranged from 18-100%.  Genetic diversity of the nematodes was investigated using the ITS and COI genes and comparing results to each other and to previously published sequences.  Nematodes had a significant impact on woodwasp body size and fecundity with infected females being smaller and producing fewer eggs than uninfected females.  Because D. proximus has been found infecting S. noctilio in the Northeast, we believe these negative impacts demonstrated on S. nigricornis will translate to the non-native woodwasp.