Emergence patterns of Sirex nigricornis F. (Hymenoptera: Siricidae) in Arkansas

Sirex nigricornis F. (Hymenoptera: Siricidae) is the only pine-inhabiting woodwasp native to Arkansas.  During their adult life span of 7-10 days females can oviposit dozens of eggs, usually in damaged or dying trees.  Larvae develop in a year, emerging in the fall.  In 2004, an invasive woodwasp in the same genus, S. noctilio F., was found in New York and has been spreading.  It causes severe damage to commercial pine stands in the southern hemisphere where it has been introduced.  Knowledge of S. nigricornis biology is critical to evaluate the risks – including timber damage and displacement of native insects – associated with movement of S. noctilio to the Southeast.  The first step is to evaluate the seasonal phenology of S. nigricornis.  Insects were collected in black panel traps during the fall of 2012 from three geographically distinct regions of Arkansas (Ozarks, Ouachitas, Coastal Plain).  Cumulative arrival curves for each geographic region were created using the number of siricids captured during each collection event.  Linear models were fit to each region for the trapping season.  There was no significance of regions or interactions with collection dates, indicating a model can be fit to the data regardless of region (R²=0.9786).  Siricid arrival rate was 1.4% per day, beginning October 8^th.  Emergence ceased by December 21^st.  Sirex noctilio in the Northeast emerges several months before S. nigricornis.  There is a possibility that S. noctilio may have access to hosts before S. nigricornis in the Southeast, greatly increasing the chance of S. nigricornis becoming displaced.