Emergence phenology and nematode associates of the woodwasp, Sirex nigricornis F. (Hymenoptera: Siricidae), in Arkansas and Mississippi forests

Sirex nigricornis F. (Hymenoptera: Siricidae) 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 a century of accidental introductions across the Southern Hemisphere. Since then, it has spread to seven states and southern Ontario. There is concern about its potential to negatively affect the multi-billion dollar pine timber industry of the southeastern United States. Effective monitoring tools are necessary to track the spread and establishment of S. noctilio. Deladenus siricidicola Bedding (Tylenchida: Neotylenchidae) is a parasitic nematode associated with S. noctilio in its native range and has been accidentally introduced along with the woodwasp. While these nematodes have been successfully used in biological control in much of the Southern Hemisphere, the strain introduced into North America appears to be non-sterilizing and is not providing natural control. Deladenus proximus Bedding is a native nematode that infects S. nigricornis and has added S. noctilio to its host range in the northeastern U.S., implicating it as a potential control agent for S. noctilio in North America, circumventing potential issues associated with classical biological control using generalists. My objectives were to 1) examine the effect of temperature on emergence patterns of S. nigricornis and S. noctilio, 2) use molecular techniques to identify the native nematode parasitizing southeastern S. nigricornis, and 3) examine the effects of nematode infection on southeastern S. nigricornis female body size and fecundity. Trapping data from Arkansas, Mississippi, Louisiana, and Ontario were examined to determine the effect of temperature on emergence of adult female siricids. Over 1,200 native female woodwasps were collected, measured, and dissected in the fall of 2011-2015 from Arkansas and Mississippi. Nematode prevalence and virulence were higher in Arkansas than Mississippi. A 750 base pair region of the cytochrome c oxidase subunit I gene extracted from southeastern nematodes was sequenced. Nematode sequences from New York and Illinois were obtained from GenBank to examine genetic diversity across the eastern United States. Genetic distance among all nematode sequences collected was less than 0.5% indicating a single species, and continuous genetic flow, of nematodes across the eastern United States. Nematodes significantly negatively impacted woodwasp size and fecundity; infested females were smaller and produced fewer eggs than uninfested females. We believe these impacts demonstrated on S. nigricornis will translate to S. noctilio. Future directions should include inoculating S. noctilio-infested trees using virulent populations of Arkansas-collected D. proximus to test these predictions in the field.

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