Study On The Semiochemicals Of Dendroctonus Valens Leconte

The red turpentine beetle (RTB), Dendroctonus vales LenConte (Coleoptera: Curculionidae, Solytinae), is a destructive forest pest infesting trunks and roots of its host. This species is a secondary pest of pines in its native locality of the North America, and has spread rapidly from Shanxi Province to three other adjacent proviences of Hebei, Henan and Shaanxi since it was found in 1998 at Shanxi Provience. With its host Pinus tabulaeformis Carr widely planted across a large portion of our contry, the potential for this exotic beetle to cause severe pines mortality is great. In this paper, the emphasis is searching whether RTBs have olfactory sensill detecting the pheromone on the antenna of RTBs. Whether adults of RTBs were attracted by females, which released pheromone after injecting juvenile hormoneⅢ; We tested the behavioral tendency of RTBs to phloem of host or adults before mating or adults mated by Y olfactory tube; The variance in relative content of induced volatile monoterpenes composition of the trunk of Chinese pine by RTBs; We analysised the volatile components of stumps infested by different treaments, and tested the effection of these components in fields; Quantitative variation of hindgut volatiles associated with RTBs at different attack phases. This methord will support the work of academic experiments in field to distinguish the sex of RTBs.In this paper we described four types of antennal sensilla of RTBs in both sexes using both scanning electron microscopy (SEM). Three subtypes of sensilla trichodea were identified, and two subtypes of sensilla basiconica. And one type of sensilla chaetica and fluted cones were distinguished on antennae of both sexes. According to transmission electron microscopy (TEM) analysis, we found sensilla trichodeaⅠandⅢcontain numberous pores on the cuticle and the lumens house numberous dendrites. This structure serves distinct chemosensory functions, which respond to pheromones. No dendrites appear in the lumen of sensilla trichodeaⅡ. Two subtypes of sensilla basiconica with pore wall and fluted cone have relationship with volatiles of host. Furthermore, evidence from dorsal morphology observation, suggests that the abdomen final segment of females is shorter than males and it is covered by the second final segment. Six membranous segments of abdomen have distinct layers, and the final segment embeds in the second one.We injected juvenile hormoneⅢsolution (2μL,10μg/μL) between 2nd and 3nd sternite region, and found females which injected JHⅢcan positively affected the attractiveness of RTBs. The JHⅢtreatment group had an obvious significant difference from the control group. Therefore, it seems that females release the pheromone after injecting JHⅢsolution. The role of phloem in the host-selection behavior of D.valens was confirmed again by Y-tube olfatometer. The result indicates that adults have strongest host preference to phloem of host and adults after mating. There is an obvious significant difference between treatments with phloem and control. We collected the volatiles odorants of the phloem and adults by headspace absorption method. GC-FID analysis showed that a few oxidized monoterpenes were detected from females after boring phloem of host such as cis-verbenol, but adults have weak response to the odor of this treatment. RTBs release oxidized monoterpenes after host phloem feeding and mating such as L(-)-verbenone and (-)-myrtenal. These volatiles odorants binding host phloem have a stronger ability to lure RTBs.The volatiles profiles of trunks of control, damaged and resistant Chinese pines, P. tabulaeformis, were extracted in headspace absorption method for eleven consecutive phases. The chemical constituents of the volatile were analyzed by GC-FID and GC-MS and their relative content of monoterpenes were determined by area normalization. Resistant pines contained significantly higher percentages of (+)-a-pinene (more than 90%) and myrcene, but lower levels of (+)-3-carene, (-)-β-pinene, camphene and limonene, when compared to control and damaged trees. The abundance of (+)-3-carene (less than 4%) in resistant pines was lower than that in control and damaged pines. However, the abundance of (+)-3-carene in damaged pines reached to the level of control pines gradually from the lower level. The content of (+)-3-carene of infested pines drops distinctly, which was induced by RTBs. The abundance of (-)-β-pinene and limonene were similar to different pines, but there are significant differences among them after infested by different sexual adults of D. valens.Stumps of Chinese pines showed the strongest attraction to RTBs and this attracton were increased with pairs of female and male of RTBs. The attration of trunks to RTBs were weaker than stumps, but stronger than logs of Chinese pines. GC-MS analysis showed that a large number of volatiles odorants were detected from stumps than trunks and logs, in which oxidized monoterpenes and sesquiterpene accounted for majority. Moreover, the maximum emission of these oxidized monoterpenes (-)-trans-verbenol had reached 0.278μg/cm2. Types of volatiles odorants from stumps were more than trunks and logs. Volatiles odorants from trunks of Chinese pines were mainly monoterpene. And types and quantity of volatiles odorants from logs were less than stumps and trunks. Thus, RTBs may enhance to release (-)-trans-verbenol, cis-Verbenol and (-)-myrtenal, when it infests a suitable host. This point was reflected distinctly in stumps with infesting beetles. The results of field test indicated that verbenone is a distinct repellant and other components increase the number of beetles trapped obviously. RTBs were collected in field from different hosts, separated into different attack phases, and immediately frozen in liquid nitrogen and taken to the laboratory. Pheromones were identified from excised hindguts by GC-FID, GC-MS, and the area of these components of GC-FID was quantified and analysed using external standard methord of GC-FID. Mytenol, trans-verbenol, verbenone, myrtenal and cis-verbenol were identified. The release amount of myrtenol was the largest among different attack phases. It appears to be an aggregation pheromone component associated with the biology of RTBs in the field. The release amount of trans-verbenol is rank only second to myrtenol, which may be one key factor for regulating the density of RTBs on the host. Verbenone and cis-verbenol appear to be multifunctional pheromones, which regulate the interspecific competition.