Differential Host Choices Of Helicoverpa Armigera And H.assulta To Tomato And Effect Of Sex Pheromone Exposure On Adult Reproductive Performance

A specialist Helicoverpa assulta and a generalist Helicoverpa armigera are two sibling noctuid species in Lepidoptera.Both species share a preferable host plant,tobacco,but they show differential responses to another solanaceous plant,tomato.Additionally,the effect of intraand inter-specific sex pheromone exposure on female reproduction performance and longevities of both sexes have not ever been paid much attention.Therefore,the author identified the active volatiles emitted from tomato leaves responsible for deterring oviposition of H.assulta,and compared the responses of the ovipositing females and the larve of both species to these volatiles,finally I tested the effect of high-dose sex pheromone exposure on female reproduction performance and longevities of both sexes.The main results are summarized as follows:(1)Dichloromethane and n-hexane could extract the active volatiles responsible for deterring H.assulta females from tomato leaves,while ethyl ether could not.All the three extracts exhibited significant ovipositional attractiveness to ovipositing females of H.armigera.The bioassay of logistic dilutions(1-,2-,4-,8-,and 16-fold)of dichloromethane extracts indicates that eggs laid by H.assulta females on tobacco leaf discs treated with all the diutions were lower than those of control.In contrast,all the dilutions shows ovipositional attractiveness to H.armigera females.(2)I detected 51 components from the dichloromethane extracts of tomato leaves.The major components were as follows:(Z)-3-Hexen-1-ol(16.27%),(+)-4-carene(12.97%),eugenol(8.61%),benzyl alcohol(6.86%),benzeneactaldehyde(6.54%),trans-2-hexenal(6.20%),1-hexanol(5.62%),2-phenylethyl alcohol(4.19%),β-phellandrene(3.82%),trans-2-hexen-1-ol(3.24%),βcaryophyllene(3.12%),p-cymene(2.5%),(+)-α-pinene(2.44%),and so on.I identified 34 components from the headspace of tomato seedling.D-limonene was the most adundant component.But most green leaf volatiles and aromatic compounds which presented in solvent extracts were not found in the headspace of tomato seedling.(3)I prepared four synthetic volatile blends based on different biosynthetic pathways(acetate-malonate pathway,acetate-mevalonate pathway,and shikimic acid pathway)and the natural ratios(GC-MS):leaf volatile-typed blend No.1(trans-2-hexenal:(Z)-3-Hexen-1-ol:traps-2-hexen-1-ol:1-hexanol=8:21:4:8),aromatic-typed blend No.2(benzyl alcohol:benzeneactaldehyde:2-phenylethyl alcohol:eugenol=10:10:6:13),terpene-typed blend No.3((+)-α、pinene:(+)-4-carene:β-phellandrene:p-cymene:β-caryophyllene=4:20:7:4:5),and a full blend No.4 with all the above-mentioned mixed in natural ratios.Test dose of active compounds was 2 μL.The results show that all the blends were deterrent to H.assulta females,among which the full blend showed the strongest effect.Only blend No.2 and No.3 showed ovipositional attractiveness to H.armigera females.All the logistic dilutions(1-,2-,4-,8-,and 16-fold)of the full blend No.4 could significantly deter ovipositing H.assulta females.Ever-increasing diluting ratios,H.assulta females could gradually accept the treated tobacco leaf discs to lay eggs,but the 16-fold dilution could still deter the ovipositing females.In contrast,only the four-fold dilution showed significant ovipositing attractiveness to H.armigera females.(4)I used tracksphere to test the approaching responses of H.assulta and H.armigera larvae to different odour sources(a tobacco seedling,a tomato seedling,2 μL blend No.4,paraffin oil control,and clean air control).The results show that the walking speeds and walking distances of H.armigera larvae to the two living plants were significantly faster and farther then to blend No.4,respectively.The inverse was true for H.assulta larvae.The sine of vector angle of H.assulta larvae to blend No.4 was the highest and significantly higher than to the tobacco plant.All the walking parameters of H.assulta larvae to tobacco and tomato odour sources did not show any significant difference,suggesting that they could not recognize tomato as a non-host plant via olfactory cue.(5)The response of H.assulta females to high-dose and long-term sex pheromone exposure was decreasing their life-time fecundity,while response of H.armigera females was delay oviposition activity.Both intra-and inter-specific sex pheromone exposures could shorten the longevity of H.assulta males,while these exposures did not affect the longevity of H.armigera males.