Olfactory Response Of Metabolus Flavescens Brenske To Host Plant Volatiles

Volatile chemicals emitted by plants play a key role in feeding,mating and laying eggs for herbivorous insects.Like most insects,Metabolus flavescens Brenske(Coleoptera:Melolonthidae)receives odor substances including plant volatile compounds through a variety of sensilla that are distributed on its antennae.To provide scientific basis for the development of effective attractants and for green pest control of M.flavescens the ultrastructure of olfactory sensilla on the antenna of M.flavescens were observed by scanning electron microscopy(SEM)to determine the type and distribution of sensilla on the antennae in the study,and the gas chromatography coupled with electroantennographic detection(GC-EAD)technique was used to identify of physiologically active components from host plants of M.flavescens.The SEM results showed that the antenna of M.flavescens comprises 4 parts:the scape,the pedicel,the funicle,and the last 3 segments forming a lamellate club.Six types of olfactory sensilla were described on the antenna of M.flavescens,i.e.,sensilla trichodea(STr),sensilla chaetica(SCh),sensilla basiconica(SBa),sensilla coeloconica(SCo),sensilla placodea(SP)and B?hm bristles(BB).There exists sexual dimorphism in length of antennal lamella.In order to conduct electroantennogram(EAG)and GC-EAG analysis using the intact lamellated antenna of M.flavescens,a surfactant,Tween~?80,was used to lower the surface tension of Beadle-Ephrussi Ringer solution.This study demonstrated that addition of 0.050%Tween~?80 to the Beadle-Ephrussi Ringer solution suppressed baseline noise and assured significantly greater EAG response in general.The antennal preparation technique described here ensures successful long-term GC-EAD recordings with scarab beetle antenna as a detector.Meanwhile,to verify the application effect of this new EAG technique,it was adapted for testing the EAG response of Solenopsis invicta Buren to alarm pheromone and its analogues.The EAG experiement deomonstrated that alarm pheromone,2-ethyl-3,6-dimethylpyrazine,and its analogues,2-ethyl-5-methylpyrazine and 2-ethyl-6-methylpyrazine,at same dose elicited similar EAG responses,indicating that these analogues are equally active as alarm pheromone component.Therefore,the EAG technique described in this study was proven to be effective in measuring EAG response in other insects.At peak occurrence of the M.flavescens,the headspace volatiles from walnut(Juglans regia L.)tree leaves,Lonicera maackii(Rupr.)Maxim,Crataegus pinnatifida Bunge,Ulmus pumila L.,Pyrus sorotina(Burm.),Syringa aromaticum(L.)Merrill&Perrytrees were collected with Poropak-Q,activated charcoal,silica gel(70-230 mesh)traps at dusk and then analyzed with the improved GC-EAD technology.The chemical identity of those volatile compounds that elicited electrophysiological responses on the antennae of M.flavescens was determined by means of gas chromatography-mass spectrometry(GC-MS).A total of 16peaks from the volatile extract generated apparent EAD responses in female antennae in a consistent and repeatable way.These peaks were identified as?-pinene,?-pinene,(Z)-3-hexenal,eucalyptol(1,8-cineole),(E)-2-penten-1-ol,(Z)-3-hexenyl acetate,6-methyl-5-hepten-2-one,1-hexanol,(Z)-3-hexenol,(Z)-2-hexenol,1-octen-3-ol,(-)-(E)-pinocarveol,(E)-verbenol,germacrene D,4-ehtylbenzyl alcohol and 4-ethylphenol.There are 23,24,24,28 and 20 kinds of volatile compounds that elicited electrophysiological responses on the antennae of M.flavescens from the green leaves of the above five host plants,respectively.Butyl acetate,Z-3-hexanal,E-2-pentene-1-alcohol,Z-3-hexenyl acetate,6-methyl-5-hepten-2-one,1-hexanol,Z-3-hexenol,nonanal,E-2-hexenol,Z-2-hexenol,Z-3-hexenyl butyrate,linalool and Z-jasmone are active compounds shared by the five host plants.1-Octen-3-ol,undecane,?-pinene and?-caryophyllene are specific to S.aromaticum,U.pumila,P.sorotina,L.maackii,respectively.Methyl salicylate,Z,E-?-farnesene,Geranyl acetoneare active compounds shared by the 5 host-plants except C.pinnatifida.E-ocimene was found in the volatiles of U.pumila,P.sorotina,L.maackii and C.pinnatifida.In addition,?-pinene,2-methyl-3-buten-2-ol,octanol and methyl salicylate that are not shared by all the 5 host plants can also induce the EAG response on the antennae of M.flavescens.These results indicate that the compounds trapped by different adsorbents from the same host plant were slightly different.