Complex Semiochemical Relationships Among Host, Nonhost Of Ips Subelongatus And Its Associated Fungi

The Asian larch bark beetle(Ips subelongatus Motschulsky) is a severe forest pest of larch all over the world, and it has caused severve damage in China. As the main fungi associated with Ips subelongatus, ophiostomatoid fungi has formed stable symbiotic relationship with the beetle. The associated community can make stronger damages than single bark beetles or single fungi. The beetle can attract male and female beetle through releasing aggregation pheromones. Individual plants can exchange the information of damage through the volatiles. These are chemical communication between individuals among the same species. Similarly, the beetles and fungi can form associated relationship through information communication. The beetle and associated fungi can find host plants and avoid the non-host plants also by chemical recognizaiton. These are all very important relations in chemical ecology. This research analyzed volatiles of host before and after innoculation damage to reveal the change of the chemical substances; field lure experiment using relevant chemical revealed the trend or escape behavior of beetles to different chemical sources; the indoor fungi culture can indicate whether relevant chemical substances had promotion or inhibition effect on fungi growth. These results were listed as follows:(1) Host volatiles before and after inoculation were analyzed. The results showed that host trees did not produce new volatile substances to defend the fungi invasion indicating no significant change of chemical components in the host. However, with the growth of the fungi, the host volatiles quantities increased significantly. The analyses of the volatiles sampled the day after inoculation revealed that terpenoid substances from the host inoculated with fungi or blank culture medium increased, but no sigficant differences were observed between the two treatments. Terpinolene, α-pinene and β-pinene are the principal volatile constituents that increased obviously. Analyses of the volatiles sampled three months after inoculation showed that terpenoid substances from host inoculated with fungi increased significantly while they dcereased from host inoculated with blank culture medium. We can conclude that host produced defense reaction as soon as receiving stimulation.(2) Field trap experiment results showed that most host volatiles increased the trapping of beetles while non host volatiles had no inhibition effect on aggregation pheromone trapping. However, host volatile r-α-pinene and non-host volatile Z-3-hexen-1-ol can significantly reduced the trapping of the aggregation pheromone indicating that the two components may be a chemical signals of host defense and non-host recognization, which needed further study in the field. We concluded that the host will increase the amounts of terpenoid after invasion of pioneer beetles, and pheromones released by beetles combined with host volatiles will attract more beetles. The non-host volatiles had non inhibition effect on trapping except Z-3-hexen-1-ol. After a long period of evolution, the beetles can recognize chemical signals. The beetles avoided the smell of the non host even if there were pheromone components presented.(3) In order to study the effects of infochemicals from Ips subelongatus, host and nonhost volatiles on the growth of its associated fungi, this study selected eight fungi strains from four species associated with I. subelongatus, cultivating with the main pheromone components, volatile components of host plants and volatile components of non-host plants. The growth of fungi showed that pheromone components(ipsenol, ipsdienol) will promote the growth and the promoting effect between different concentration changed very little. Host volatile components strongly inhibited the growth of fungi. The more increase of non host volatile concentration, the more inhibition effects were observed, and when the concentration reached a certain level, the growth will be inhibitted completely. We concluded that the aggregation pheromones fo bark beetles can promote the growth of associated fungi, which lead to strengthen the associated relationship. Host volatiles restrain the growth of associated fungi, which lead to weaken the harm produced by the associated relations, the inhibition effect of nonhost plant may weaken the injury of the fungi.