| The diamondback moth(DBM),Plutella xylostella(L.),is a globally destructive pest of cruciferous vegetables.Due to the excessive and single use of chemical synthetic pesticides,the moth,which is very difficult to control,can rapidly evolve high resistance to numerous available insecticides.Plant volatile secondary metabolites play an essential role in the survival and reproduction of insects,and have a certain impact on insect behavior activities such as locating host,looking for spouse,looking for suitable oviposition place and seeking advantages and avoiding harmful substances.China is rich in plant resources.The prevention and control of the DBM by more safer,efficient and low toxicity non-host plants or their natural products is a hot issue in present research.In this study,thirteen species of non-host plant essential oils(EOs)were selected to determine the bioassay against DBM larvae and adults,and the sublethal effects of LC25 and LC50 were determined by using the EO with the best activity.The same EO was selected,and the volatiles of its plant leaves were collected in headspace.The active components with repellent effect on DBM were identified by GC-MS and GC-EAD,and the activities were verified.Furthermore,the effective repellent range and effective repellent longevity of the best component was determined.The application effect of the best active substance was tested in the field environment.Meanwhile,the molecular mechanism of the active components against DBM perception was preliminary studied by transcriptome technology.The results of this study are as follows:1.Bioactivity of thirteen species of plant EOs against DBM larvaeThirteen species of EOs had different biological activities against DBM larvae.The most toxic EO was Pelargonium × hortorum(24 h: LC50=0.75 μg/μL,48 h: LC50=0.49 μg/μL and 72 h: LC50=0.36 μg/μL)against second-instar larvae,followed by Polygonum hydropiper(24 h: LC50=0.91 μg/μL,48 h: LC50=0.68μg/μL and 72 h: LC50=0.53 μg/μL).The Ocimum basilicum EO exhibited the highest antifeedant effects to third-instar larvae at all set concentrations,the antifeedant rates were 83.16%,98.63% and 100%respectively.At 7.5-15 μg/μL,the EO of P.× hortorum showed higher antifeedant activities of larvae,and the antifeedant rates were 83.16%,98.63% and 100% respectively.The Ruta graveolens EO showed the lowest relative growth rate and the highest growth inhibition rate towards third-instar larvae at diverse concentrations.And the EOs of P.hydropiper,O.basilicum,Acorus calamus,P.× hortorum,and Pogostemon cablin showed promising growth inhibition activities.At the test concentration of 15 μg/μL,the weight of larvae was increased negatively,this means the relative growth rate was negative,and the growth inhibition rate was more than 100%.Among the thirteen species of tested EOs,P.× hortorum had the strongest biological activity against DBM larvae.Treatment with LC25 and LC50 of P.× hortorum essential oil had a few effects on the survival rate,pupation rate,pupal weight and emergence rate of the third-instar larvae.There was no significant difference in adult sex ratio,total eggs per female and hatchability.Overall,LC50 treatment had a strong effect on larvae than LC25.2.Behavioral response determination of thirteen species of plant EOs to DBM adultsThe female and male adults of DBM can produce EAG response to all plant EOs at the test concentration,and the response value is positively correlated with the concentration of EOs.The P.×hortorum EO had the strongest electrophysiological response to female adults at all tested concentrations,the EAG values were 0.22±0.05 m V,0.57±0.12 m V,0.72±0.07 m V and 0.73±0.10 m V respectively;Perilla frutescens and Chenopodium ambrosioides EOs were highly sensitive to male adults at four tested concentrations.The results of behavioral response showed that P.× hortorum EO had a significantly repellent effect on female and male adults,and the repellent rates of female and male adults were not less than 66.67% and 63.33%,respectively;the other twelve species of test EOs also had different degrees of repellent behavior.3.Active components in P.× hortorum volatiles that can repel DBM adultsThe behavioral response of DBM to P.× hortorum leaves in different physiological states showed that the mechanically damaged leaves had a stronger repellent effect on adults.The active compounds of volatiles from damaged plant against female adults of DBM collected in headspace are myrcene,γ-terpinene,linalool,camphor,and terpinen-4-ol,their relative ratio is 1:5:3:4:3.The results of antennal and behavioral response showed that there were small differences in response of female adults at two mating states,and the response threshold of mating female adults was relatively large.The oviposition assay in net cage showed that blend-2(the ratio of five compounds was 1:5:3:4:3)had the strongest oviposition repellent effect on female adults,and the oviposition index was –0.83.Furthermore,it can significantly reduce the number of eggs.The net room test found that the slow-release blend-2 had an effective repellent range of 0.9 m,and the effective repellent longevity was 26 days.The field experiment showed that the slow-release blend-2had obvious repellent effect on the oviposition of females at 1th,3th,5th and 7th day,and decreased at 14 th day,but there was still a significant difference compared with the control.4.Olfactory genes of female DBM adults perception the P.× hortorum active substancesThe antennal transcriptomes of females adults treated with active substance blend-2 was performed.Compared with the control,totally 560 differentially expressed genes(DEGs)in the antennal transcriptome of females adults were identified,including 330 up-regulated genes and 230 down-regulated genes.There are two differentially expressed chemosensory genes,including odor binding proteins Pxyl OBP8 and Pxyl OBP13.They may be target genes for perception active repellent odors of P.× hortorum.The EO of P.× hortorum was selected from 13 non-host plants.It had the strongest biological activity against DBM larvae and had a significant repellent effect against adults;The active compounds mediated by P.× hortorum volatiles to repel the oviposition of female adults were identified,and the best substance was selected,and the repelling activity was verified in the laboratory and field;It is also proved that Pxyl OBP8 and Pxyl OBP13 are chemical genes of receptive blend-2 in female adults.This study can provide theoretical bases and technical supports for the integrated management of DBM and a potential molecular target for the development of a new oviposition repellent for DBM. |
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