Semiochemical Based Host Selection Mechanism Of Three Tomicus Spp. Attacking Yunnan Pine During Shoot-feeding Phase

Tomicus yunnanensis Kirkendall & Faccoli, T. brevipilosus and T.minor are the most important forest pests of Yunnan pine(Pinus yunnanensis)which cause a large amount of the tree death every year. The three beetles are small, hidden, breed rapidly, damage seriously and difficult to control, so it is inevitable to establish forecasting and controlling system. Previous studies focused on their stuck attacking period, while there were fewer studies during shoot feeding period. The three beetles damage Yunnan pine together in forest. They need to transfer from shoots to shoots to satisfy the need of nutrition, so there were more chances to expose in outside of shoots, which is profitable for attraction. Therefore, it is important to study about semiochemicals during this phase.In this study, we aimed to explore the semiochemical based host selection mechanism of the three Tomicus species during shoot feeding period through GC\GC-MS analysis and the walking biological assay. The paper including three aspects: biological assay of three Tomicus species during the shoots feeding phase to volatile extracts from branches; analysis of the major volatile components of the branches damaged by three Tomicus and their hindguts; biological assay of three Tomicus species to single and mixed volatiles. The results are as follows:1. Biological assay showed that: all of the beeles displayed a higher positive response rate to extracts of damaged shoots of P. yunnanensis, whereas a lower response rate to shoots of Pinus armandi. There was no significant difference between T. brevipilosus and T. minor to the extacts of healthy and barkbeele-attacked Yunnan pine branches, while T. yunnanensis obviously selected that of damaged shoots of Yunnan pine compared the healthy ones. These results indicated that the Tomicus during shoot feeding period used volatile odors for host location.2. Analysis of GC and GC-MS showed that: the content of some volatiles were clearly different between branches attacked by T. yunnanensis and the healthy ones. Comparing to healthy branches there were significantly more myrcene, camphene, β-pinene and β-caryophyllene in attacked ones, while 3-carene was remarkable less;the content of(+)-linmone in branches attacked by T. minor and the content of 3-carene in branches attacked by T. brevipilosus was lower. Volatiles from hindguts of the three beetles varied in composition and content. There were the most volatile compounds in T. brevipilosus, while the least in T. minor. The content of myrcene was higher in hindguts of T. yunnanensis compared to others. The results provide a theoretical basis for further studies.3. The responses of three Tomicus species to single component of host monoterpenes and beetle pheromones were tested by walking bioassay. The result showed that the three Tomicus species had obvious positive response to part of monoterpenes compounds. T. yunnanensis during shoots feeding period had more obvious taxis for compounds A, B, C, E in certain concentration, T. minor during shoots feeding period had obvious taxis for compounds A, B in concentration of 100ng/μL, T. brevipilosus during shoots feeding period had obvious taxis for compounds A, B, C, E, G, H and T. brevipilosus during from shoots to trunks period had obvious taxis for compounds B, C, D, E, G respectively. Moreover, the three Tomicus had obvious responses for pheromone I, J, K.4. The bioassay results of the three Tomicus species from shoot feeding phase and T. brevipilosus from stuck attacking phase to mixed componds showed that: mixtures V、VII and XIX were effective to T. minor; mixtures II、XVII and XVIII were effective to T. yunnanensis; T. brevipilosus from shoot feeding period displayed a higher positive response to mixtures IV、V and VI, while from tuck attacking phase displayed a higher positive response to mixtures I、VI and VII. Mixture V was effective to both T. yunnanensis and T. brevipilosus from shoot feeding period. Mixture IV was effective to T. brevipilosus from shoot feeding period specially. Mixtures VII、XIX were effective to T. minor from shoot feeding period specially.