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

Chengcheng Li,Lili Ren,Jiahe Pei,Xiaobo Liu,Youqing Luo,Jiale Li

doi:10.3390/insects12020116

Abstract

Simple SummaryThe cold tolerance strategy of Sirex noctilio overwintering larvae was freeze-avoidance and their supercooling points adjusted seasonally to avoid icing damage. The cold hardiness between different populations varied on a spatiotemporal scale; specifically, the harsher the environment, the stronger the cold tolerance of overwintering Sirex noctilio larvae. A tunnel played a certain protective role but did not affect the low temperature parameters limiting the distribution of S. noctilio. We provide experimentally determined low temperature limiting parameters of Sirex noctilio and prove it has the opportunity to spread and colonize in other regions.Sirex noctilio (Hymenoptera: Siricidae) is an invasive pest that has spread and established in many regions worldwide. However, its cold tolerance strategy is still unclear. We measured the supercooling point (SCP) and the lower lethal temperature (LLT) of overwintering S. noctilio larvae during three overwintering periods in four geographically separated populations in China. In addition, using the statistical analysis of the local historical temperature data, we also conducted comprehensive studies of S. noctilio cold tolerance variations and strategies. We measured the SCP of all samples as S. noctilio could survive at its SCP during a short period of exposure (<48 h) and its cold tolerance strategy was freeze-avoidance. The average SCPs of the groups in different spatiotemporal scales were significantly related to average temperature variation with most individuals exhibiting stronger cold hardiness at low ambient temperatures. S. noctilio exhibited a strong cold tolerance and it has the ability to withstand lower temperatures in cold environments. The geographic population showed a positive tendency as the ambient temperature decreased, which would increase its chance of developing in cold regions.

Highlights

We investigated the cold tolerance of S. noctilio by measured supercooling point (SCP) of four geographic populations and combined these with lethal temperature (LLT)
According to the two categories divided by the SCP, we found that the northern and southern sites significantly differed in their daily average temperature (t = −2.85; df = 1, 1458; p < 0.01) (Figure 4b)
S. noctilio could not survive for extended periods at temperatures below their SCPs and of S. noctilio could not survive for extended periods at temperatures below their SCPs and their lethal temperature causing 50% death (LLT50) values were similar to their SCPs

Summary

Introduction

Sirex noctilio Fabricius is an invasive woodboring wasp that attacks Pinus spp. It has become one of the most important pests in softwood plantations of the Southern. Hemisphere [1,2,3,4,5]. In 2013, S. noctilio was found in Daqing, Heilongjiang Province in northeastern China, for the first time [6]. As reported [7], individuals of this species were successively found in Heilongjiang Province, Jilin Province, Liaoning Province and Inner

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