The Genetic Variation Of Ips. Subelongatus In Northeast China

The Asian larch bark beetle, Ips subelongatus Motschulsky (Coleoptera:Curculionidae: Scolytinae), is a severe forest pest of larch in northeastern China, and causes significant damage in plantations and natural stands resulting in huge economic losses and ecological damage. Because of its small size, hidden life and breed rapidly, it is very difficult to control. So it is high time to find an effective method to monitor and control this pest. Combined with the research of molecular phylogeography, this study assayed the differences of behavioral responses to major aggregation pheromones among six different I. subelongatus geographic populations in northern China. Furthermore, the electrophysiological activities of the antennae of I. subelongatus to major aggregation pheromones were also conducted by the mothods of electroantennogram (EAG) and gas chromatograph-electroantennographic detector (GC-EAD). In addition, the headspace volatiles from the barks and needles of Dahurian larch (Larix gmelinii Rupr.), Prince Rupprecht larch(Larix principis-rupprechtii Mayr.), and Korean larch (Larix olgensis Henry) were entrapped by the method of dynamic headspace collection technique, and then the hexane elution was analyzed by chiral gas chromatography (GC) and GC-mass spectrometry (MS) in order to identify the volatiles. Also, we used GC-EAD and EAG to assay the olfactory sensitivity and selectivity of I. subelongatus to synthetic volatiles identified from leaves and bark of three species of host trees. These results were listed as follows:(1) twenty seven mtDNA COI haplotypes were identified, in which haplotypes HT2, HT5, HT1and HT6showed high frequency in individuals tested. HT2haplotype was considered the oldest haplotype of I. subelongatus in northern China. Haplotype HT5were principal shared in individuals from populations of HSJL and EDJL and HT2was not found in this distribution ranges. Low average nucleic acid variability within populations (0.6%) revealed that I. subelongatus did not form independent subspecies. Molecular variation is closely related to the localities and hosts.(2) Electroantennogram sensitivity to major pheromone components97%-(S)-(-)-ipsenol and97%-(S)-(+)-ipsdienol was0.1μg in dose-response analyses, with no quantitative differences among the six populations tested. However, populations varied in their responses to (R)-(-)-and (S)-(+)-ipsdienol in gas chromatography-electroantennographic detection (EAD) analyses. The preference for (S)-(+)-ipsdienol showed two EAD response patterns, which correlated with geography and climate. Antennae responded most strongly to (S)-(-)-ipsenol (100%detection;0.35-0.73mV) at the50-ng stimulus level, while its antipode,(R)-(+)-ipsenol was antennally EAD-inactive.(3) A binary blend of97%-(S)-(-)-ipsenol and97%-(S)-(+)-ipsdienol was critical for mass trapping; attraction was interrupted by (R)-(+)-ipsenol and/or (R)-(-)-ipsdienol. However, increase the proportion of (-3/+97)-ipsenol and (-97/+3)-ipsdienol had a certain inhibitory effect for I. subelongatus aggregation but different regions had different inhibition strength.(4) We totally identified12monoterpenes, which mainly consists of s-(-)-a-pinene, r-(+)-a-pinene,(+)-3-carene, r-(+)-β-pinene, and s-(-)-β-pinene accounting for more than80%of the total collected monoterpenes.(5) Ips subelongatus had EAD responses to p-cymene,(+)-3-carene, s-(-)-α-pinene,(+)-limonene, y-terpinene, and terpinolene; the tested I. subelongatus feeding on different Larch species showed different EAG responses to host volatiles at100ng stimulus loads:a strong EAG response to (+)-3-carene、(+)/(-)-limonene、Myrcene were observed and the response value was significant different among individuals of I. subelongatus feeding on different Larch species; a weak EAG response was observed to (+)/(-)-camphene, and the response value was not significant different. With the increase of stimulus loads, EAG response would be stronger. EAG responsiveness to synthetic monoterpenes was not correlated with the proportion of released host volatiles, this might be explained partly why the I. subelongatus cannot attack the healthy host trees under the normal condition. (6) All the species with cuticular hydrocarbons analyzed have the Kovats retention indices (KIs) with a range of2300-3000, which showed differences of quality and quantitiy in different species. However, no sexually dimorphic characteristics of cuticulat hoyrocarbons were observed in the species sampled. The main hydrocarbons contain methyl-branched alkanes, followed by n-alkanes.The cuticular hydrocarbons as the chemotaxonomic characters can effectively distinguish different species in our analyses and can be used to study phylogenetics at the level of species.Although there are some difference of hydrocarbons in different Ⅰ. subelongatus geographic populations,the low level of difference was not suitable to analyse the geographic populations of phylogenetic.