Structural Identification And Behavior Activity Bioassay Of Semiochemicals Of Juniper Bark Borer Semanotus Bifasciatus Motschulsky

The Juniper bark borer Semanotus bifasciatus Motschulsky(Coleoptera: Cerambycidae)is unique coleopteran pest in East Asia,And widely distributed in Northeast China,North China,Northwest China and East China,as well as Korea and Japan,causing destructive damages on Cupressus spp.,Platycladus spp.,Sabina spp.,Chamaecyparis spp.,Juniperus spp.,and Thujopsis spp.,especially posing a great economic threat on Chinese.The adults having multiple mating habit prefer the weak trees or the freshly felled trees to lay eggs.The larvae tunneled in the xylem of the trunk,which cut off or destroyed conducting tissue and affected the nutrient transport leading to the death of the host.This cryptic damage habit made it very hard to control with pesticides.To aid in the management and controlling of this pest,and the changes in the content and proportion of hydrocarbon components in the cuticular hydrocarbons of S.bifasciatus may cause changes in the corresponding biological functions,and further clarify the.existence and effective ratio of sex recognition pheromone and host bentamine.In this study,gas chromatography and gas chromatography-mass spectrometry(GC-MS)were used to analyze the cuticular hydrocarbons extract with two different methods and volatiles of Platycladus orientalis,and field experiments were carried out to virify the result.The analysis results are as follows:(1)GC-MS analyses of the CHCs from different developmental stages of S.bifasciatus demonstrated the presence of three homologous series of alkanes: n-alkanes from C15 to C31,monomethylalkanes,and dimethylalkanes.Of the total hydrocarbons in the body wall of the larvae,the n-alkane series from C15 to C31 accounted for 80.07%,with the major component being n-heptacosane,27.97%;of the methylalkanes,it was 3-methylpentacosane and 11,15-dimethylheptacosane,accounting for 19.93%.The n-alkane series accounted for 60.42% of the total hydrocarbons in the newly emerged females,74.15% in newly emerged males,53.13% in flying stage females,and 45.99% in flying stage males.In the branched-chain series,the newly emerged female elytra accounted for 39.58%,the newly emerged male elytra for 25.85%,the flying stage female elytra for 46.87%,and the flying stage male elytra for 54.01% of the total hydrocarbons.Major components consisted of n-pentacosane in male and female adults.With the development of the S.bifasciatus from larvae to adult,the contents of n-alkanes showed decreasing trend and the methyl-branched alkanes indicated increasing trend.The change of CHCs from solvent extract showed the same trends as the SPME sampling method.During 1-6h and 12 h freezing under-20℃,the content of CHCs of S.bifasciatus adults didn’t show a decreasing tend.It was confirmed that the CHC were stable in a short time and could be stored at low temperature for a period of time to maintain their specificity.(2)The cuticular hydrocarbons of male and female S.bifasciatus were analyzed by GC and GC-MS.The results showed that there are similar types of composition in both sex adult from SPME sampling and hexane extract sampling.However,amounts and ratios of individual compounds were considerably different between males and females.Three 11-methylbranched alkanes were identified as: 11-methylpentacosane(11Me-C25),11-methylhexacosane(11MeC26),and 11 methylheptacosane(11Me-C27),which possessed 16.12% of total amount of cuticular wax in female and 17.49% in male.These 11-methylbranched hydrocarbons were associated with live female elytra in a ratio of 10:1.3:6.2(11Me-C25 : 11Me-C26 : 11Me-C27)(determined by SPME).In laboratory bioassays,a centrifuge tube coated with a synthetic blend of these three compounds with above ratio could evoke about 83% male mating behavior within 22 seconds after contact.The results suggested that these three 11-methylbranched hydrocarbon with natural ratio determined from female could act as contact sex recognition pheromone of male Juniper bark borer,S.bifasciatus,therefore,our hypothesis was experimentally confirmed.Successful mimicry of chemical communication for S.bifasciatus may facilitate technical solutions to manage this pest.(3)The volatile consituents of the trunk of P.orientalis,are mainly composed of n-alkanes of C9-C20,sesquiterpenes,monoterpenes and their oxides.Among the monoterpene components,the content of 3-pinene is the highest,and the content of alpha-pinene is similar to the beta-pinene,and the ratio of three componts is about 12: 4 : 3.The results of field trapping experiments showed that the mixture of monoterpenes and sesquiterpenes from the volatiles of P.orientalis had significant synergistic effect on the trapping of S.bifasciatus.Among that,the experimental group with cedrone and cuparene had the best effect,while cedarene had no fear of synergism or inhibition on the trapping effect.These findings suggest that cedarene may be one of the components of host defense signals,and further research is needed.The above results indicate that the host bentamine has good application prospects in forest control and trapping of S.bifasciatus.