Emergence of adult female Sirex nigricornis F. and Sirex noctilio F. (Hymenoptera: Siricidae) coincides with a decrease in daily minimum and maximum temperature.
The establishment and spread of Sirex noctilio F. (Hymenoptera: Siricidae), in northeastern North America necessitates reliable monitoring methods for this alien woodwasp pest of Pinus. The native congener, Sirex nigricornis F., is common across the eastern U.S.A. and has been studied as a proxy for S. noctilio. Predicting the emergence of S. noctilio is important for guiding monitoring efforts. Degree-day models have been developed to predict flight phenology of S. noctilio and S. nigricornis across eastern North America. These model parameters were tested against three years of S. nigricornis collections from two locations in Arkansas. Neither of the proposed models accurately predicted emergence. The emergence of females for both S. noctilio and S. nigricornis was significantly negatively correlated with minimum and maximum temperature, indicating that emergence increases when minimum and maximum temperatures decrease. These results suggest that, as S. noctilio spreads south, where higher mean temperatures are present, it will emerge later in the season as the temperatures decline compared with the current northeastern population. We propose that monitoring for the spread of S. noctilio in the southeastern U.S.A. should begin slightly before daily temperatures are expected to decline (i.e. mid-September).