Thermal survival limits of larvae and adults of Sirex noctilio (Hymenoptera: Siricidae) in China

Temperature can be a major factor for the distribution of insects, especially among invasive insects. Sirex noctilio (Hymenoptera: Siricidae) has invaded many regions in China, causing enormous ecological and economic losses. We aimed to explore the trend and potential of diffusion by researching the thermal survival limits of S. noctilio. We measured the supercooling point (SCP), critical thermal temperature (CTmax), high lethal temperature (HLT) and low lethal temperature (LLT) for S. noctilio population in China and assessed life stage-related variation in thermal tolerance. Moreover, we determined the temperature tolerance range of S. noctilio and identified the temperature parameters for its potential invasive distribution risk analysis. The SCP of adults was -11.78 ± 0.67 (mean ± SEM), the CTmax was 37.67 ± 0.54, and those of larvae were -20.77 ± 0.44 and 40.53 ± 0.27, respectively. The LLT increased with exposure time, and the HLT was generally near 43°C. S. noctilio adults can tolerate higher temperatures than larvae, and the larvae showed high resistance to cold temperature. We calculated several temperature indexes based on our results, such as the lower temperature threshold (DV0) at -2.7°C, the upper temperature threshold (DV3) at 31°C, the temperature threshold for both heat stress (TTHS) at 35°C and cold stress (TTCS) at -32.5°C. We observed that, S. noctilio was not resistant to high temperatures, its CTmax is slightly lower than the lethal temperature, and the adults were more tolerant than larvae. Our next goal was to combine the temperature tolerance of symbiotic fungi, information on climate change and the current distribution of this species to predict its potential global distribution.