Abstract:

【Objective】 Poplars are important tree species in plantations and timber in China. We aimed to identify the species of the JSYC-beetle strain in dead poplar and determine its risk, and provide a theoretical reference for the control of the beetle. 【Method】 The head, pronotum, antennae and elytron of the beetle were observed and measured by the traditional morphological identification method. The DNA of the beetle was extracted by using the CTAB method, and the corresponding COI, 28S rDNA and CAD regions were amplified. The amplified products were sequenced and spliced by biological companies, homology analysis was conducted on the NCBI website, and similar sequences with the top 10-15 homology were selected to construct three gene phylogenetic trees by using the NJ method. According to the clustering results of the phylogenetic tree, JSYC-beetle strain were identified. In order to predict the possible damage degree, the distribution and potential hazards of the JSYC-beetle in China were analyzed according to the quantitative analysis method of pest risk assessment.【Result】 The female JSYC-beetle was reddish-brown to black, with a body length of 3.3-3.7 mm and a width of 1.49-1.64 mm. The male was yellowish-brown, with a body length of 2.264 mm and a body width of 1.195 mm. The insect body had a metallic luster. The flagellum had five segments, and the length of the first segment was shorter than that of the other segments. The end segments of the antennae were spherical, with two obvious transverse seams. The compound eyes were kidney shaped. The head was hidden in the anterior sternal plate. The anteroposterior plate was nearly square in shape and protrudes. The front edge was wide and round, and its width was slightly larger than its length. The front part was distributed with squamous teeth, and the latter part was smooth. The scutellum was ligulate, and the width of the elytron was slightly larger than that of the pronotum. The oblique plane of the elytron gradually inclinesd from the base to the end. The elytron was shaped similarly to a tongue. The size of the incisions on the intercostal part of the elytron was similar to that in the groove, and the distribution was uniform. There were 8-14 odontomas in the tibial segment of the forefoot, and the first segment of the trasi was shorter than the sum of the other segment lengths. According to the aforementioned morphological comparison, the morphological characteristics of the bark beetle JSYC-beetle strain were most similar to those of E. interjectus. The COI, 28S rDNA and CAD genes were amplified by agarose gel electrophoresis. The results showed that COI, 28S rDNA and CAD genes could amplify single and bright bands and that the size of the electrophoresis band was 700-1 000 bp, approximately 500 bp and 400-500 bp, respectively. The results of NCBI sequence alignment showed that the COI, 28S rDNA and CAD sequences had the highest homology with E. interjectus, with similarities of 99.14%, 99.38% and 99.36%, respectively. The phylogenetic tree showed that the JSYC-beetle strain was clustered in one branch with E. interjectus, further indicating that the JSYC-beetle had the closest relationship with E. interjectus. On the basis of these results, the JSYC-beetle was identified as E. interjectus. The results of risk analysis showed that the risk R value was 2.01, which was a high-risk organism in China. 【Conclusion】 The bark beetles in dead poplar trees are E. interjectus, a high-risk organism in China. The beetle may harm healthy poplar and has been collected from poplars in China; there are many dead poplars in the collection area. Therefore, strengthening management to prevent major harm to poplar and other host plants is necessary.

Key words: Euwallacea interjectus, poplar, morphological identification, molecular identification, risk analysis