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

Abstract

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.

Overwintering Larval Cold Tolerance of Sirex noctilio (Hymenoptera: Siricidae): Geographic Variation in Northeast China

“…Based on preliminary assays, most S. noctilio larvae could survive at temperatures lower than their SCP. The LLTs of total populations have been calculated before [ 13 ]. The larvae from Yushu City, Jilin Province (YS) were selected for the low temperature exposure experiment during the mid-winter period, which was chosen because the lowest SCP measurements indicated the peak of cold tolerance at that time [ 13 ].…”

“…After completing the treatment, the samples were placed in a standard environment (25 °C, dark:light = 24:0 h, relative humidity = 75%) for 2 h and the body of each larvae was poked with a probe to determine whether it was alive. The damage to insects caused by the low temperature and the ability of insects to resist low temperatures were evaluated by calculating the lower lethal temperature causing 50% death (LLT 50 ) and 99% death (LLT 99 ) [ 13 , 16 ].…”

“…The LSD and Games–Howell tests were the post hoc tests used with the ANOVA. We followed the methods of Li et al, Feng et al and Li et al to analyze the SCP and MP data [ 13 , 20 , 23 ]. A test of the homogeneity of variance was performed for one-way ANOVA to meet the normality criteria better and a t -test was performed between each pair of samples to obtain p -values.…”

“…The relationship between the MP and the SCP was analyzed using Unpaired t -test data (after a Bonferroni-test and Bonferroni-corrected, p < 0.05). LLT 50 and LLT 99 were calculated [ 13 , 18 , 19 ] and the latter was used to evaluate the damage to insects caused by low temperatures and the ability of the insects to tolerate the low temperature. Data analysis consisted of the Probit method implemented in regression analysis in SPSS 23.0.…”

“…During the cold winter season, larval woodwasps enter the diapause within deep tunnels of host trees [ 12 ]. We measured the supercooling point (SCP) and low lethal temperature (LLT) for its population in China and described its thermal survival limits [ 13 ]. However, the cold tolerance strategy and climate variability of S. noctilio are not clear.…”