Research On Interspecific Interaction In Pinewood Nematode And Monochamus Alternatus Hope Mediated By Ascarosides

Ascarosides was found in C. elegans, a kind of chemical information in substance secreted by the nematodes, regulate their own behavior and development. In recent years with the discovery of nematode pheromone ascarosides, chemical communication function in the nematode induced behavior and development, but the research object less focused on the field of insects. Pinewood nematode(Brusaphelenchus xylophilus) is China’s major foreign biological invasion, and form the co-evolutionary relationship with media pine sawyer ink (Monochamus alternatus Hope). Enter winter, the pinewood nematode and instar larvae of pine sawyer ink enter diapause at the same time in the same microhabitat (pine sawyer ink pupal chamber). In this study with nematodes diapause pheromones, our group accidentally discovered pine sawyer ink surface containing nematodes ascarosides pheromone components, and keep longicorn in diapause larva stage. So, the nematodes and pine sawyer ink provide the research model for chemical communication and universality of the mechanism inducing diapause development conservative. This paper illustrates the intraspecific and interspecific information communication between nematodes and pine sawyer ink within the development and regulation of diapause, and will further analysis the interdependent co-evolutionary relationship of insects and nematodes. The main results were as follows,1. The individual development of media pine sawyer ink is closely related to the occurrence of pinewood nematode.Inquire into the larvea and adults of pine sawyer in four locations generating region, such as Tianwangshan (Shaanxi province), Nanlushan(Shaanxi province), Jiangjunshan(Jiangsu province), Leshan (Zhejiang province), we found that even certain radioactive-polluted area in the north has higher altitudes and the lower temperature and precipitation, the northern larvae and adult individual beetles were bigger than the south, and the number of nematodes is much higher than the south. Nematodes influence beetles’pupate in advance. The amount of Lm nematodes around the pupa chamber increases with larvae beetle weight increases. The amount of LⅣ nematode carried by beetle adults increases with adult weight increases. In order to further illustrate that nematodes influence on the development of pine sawyer ink, we further investigated the pine sawyer ink adults in nematode occurrence area and unoccurrence area with similar abiotic factors, we found the individual size of pine sawyer ink in unoccurrence area were significantly less than nematode occurrence area.2. Pine sawyer surface contains a series of ascarosides, and asc-C9 is the diapause pheromone of it.With the chemical extraction analysis on surface ascarosides of Pine sawyer ink in different temperature larva (including larvae at low temperature and larva at room temperature,), we found that the low temperature larva is higher than normal temperature larvae in asc-C9 content. Asc-C9 grow determine found it inhibit the larvae pupate. It shows that pine sawyer ink contained asc-C9 within itself can restrain its development, thus prepare the conditions for overwintered by the state of old larvae.3. The specific ascarosides components——asc-C5, asc-ΔC6 and asc-C6 on surface of nematodes and pupa chamber of pine sawyer ink can promote the growth of pine sawyer ink larvae.Under the normal temperature, pine sawyer ink development process speed up in artificial pupa chamber with nematodes. Feed larva beetles with extraction from pupa chamber, larvae development speed accelerated. Ascarosides chemical extraction analysis of natural pupa chamber, artificial pupa chamber and nematodes surface found that asc-C5, asc-ΔC6 and asc-C6 were nematodes specific ascarosides, these three ascarosides components can promote the pupate of pine sawyer ink larvae, it instructed that when spring coming in next year, large amounts of pine wood nematode Lm gathered around the pupa chamber of pine sawyer ink, nematodes can affect the growth of pine sawyer through chemical regulation of ascarosides, enable it to carry by pine sawyer earlyer and complete the next round of infection cycle better.4. Asc-C9 can control the concentration of juvenile hormone levels in pine sawyer ink larvae, delayed larvae pupate. Asc-ΔC6 is able to regulate the concentration of ecdysone in pine sawyer ink larvae, advanced larvae pupate.In conclusion, this study speculated that ascarosides mediated the synergistic interactions between nematodes and pine sawyer ink, the pine sawyer producted pheromone asc-C9 on low temperature, maintain growth stagnation, after winter, pine sawyer pheromone secretion is reduced, the LⅢ nematode gathered themselves together, and the asc-C5, asc-ΔC6 and so on play a role in promoting the process of pine sawyer larvae’s pupation.