Study On Toxicity And Oviposition Inhibition Of Plant Essential Oils Against Tetranychus Urticae

Tetranychus urticae Koch is one of the main pest mites in fruit and vegetable production in China.Due to its short development duration and strong breeding capacity,the population number can be rapidly increased in a short time.However,the resistance of T.urticae is increasing due to the excessive use of chemicals.Therefore,some control measures with high safety and good control effect are urgently needed to delay the development of its resistance.Plant essential oil is extracted from various plants in nature with a high extraction rate.It is safe for the ecological environment and human body and widely used in all walks of life.In recent years,the application and development of essential oils in agriculture have attracted much attention,but the related research on the control of pest mites was little.In this study,40commercially produced plant essential oils were selected for the experiment.The indoor toxicity test and oviposition inhibition comparison of T.urticae were conducted using the leaf-dip feeding method to eval-uate the acaricidal activity of each essential oil and its impact on the reproductive ability of female adult mites.On this basis,ten essential oils with significant biological activity were selected for determination by GC-MS to analyze the compound components,and the toxicity test and egg-laying inhibition study on the main compound components were conducted to screen out the plant-derived compounds that can be used for the control of T.urticae.The specific results of the study are as follows:1)Laboratory efficacy results showed that 13 of 40 plant essential oils exhibited certain acaricidal activity at a concentration of 4μL/m L,and the mortality of T.urticae was significantly higher than that of the control at 72 h after treatment（p≤0.01）;The indoor toxicity comparison was conducted for seven essential oils with the average mortality rate exceeding 25%at 72 h.The lemon essential oil had the highest toxicity to T.urticae(LC₅₀ of 2.310μL/m L),followed by sage,patchouli,olibanum,lemongrass,palmarosa,and oregano essential oils,with LC₅₀ of 3.684μL/m L,4.202μL/m L,4.611μL/m L,6.196μL/m L,6.887μL/m L,and 9.123μL/m L,respectively.2)The study of oviposition inhibition showed that 18 kinds of essential oils showed a certain inhibi-tory effect at the concentration of 4μL/m L after 72 h treatment.The inhibition rate and inhibition index of lemon essential oil are the highest,which are 99.15%and 0.98,followed by sage,frankincense,clove,lemongrass,oregano,patchouli,myrrh,black pepper,palmarosa,and geranium essential oil,with the in-hibition rate exceeding 50%,while the inhibition effect of bergamot,basil,cypress,citrus,juniper,rose and vetiver essential oil is weak.At this concentration,the toxicity of black pepper,clove,myrrh,and oregano essential oils to T.urticae was low,but their oviposition inhibitory activity was high.3)By GC-MS analysis,it was found that（-）-Isocaryophyllene was the common component in 7 es-sential oils,and the content was the highest in the clove essential oil.β-Myrcene and limonene were detected in 6 essential oils,and limonene was one of the main components in palmarosa,lemon,and lemongrass essential oils.In addition,linalool,α-caryophyllene,（-）-caryophyllene oxide,（-）-β-elemene,（+）-δ-cadinene,p-cymene andβ-pinene are also widely present in a variety of essential oils.4)According to the results of GC-MS analysis,the acaricidal activity and oviposition inhibition ac-tivity of some compounds which are widely found in essential oil with low cost was further determined,among which carvacrol,eugenol,and citronellol have higher toxicity to T.urticae,and the LC₅₀ after 72h treatment is 6.577μL/m L,10.594μL/m L and 12.776μl/ml respectively;The toxicity of geraniol is relatively low,but its LC₅₀ is still lower than 20μl/ml.However,citronellal and benzyl alcohol have poor toxicity,with LC₅₀ of 46.124μL/m L and 80.307μL/m L respectively.In the aspect of oviposition inhibi-tion,carvacrol and eugenol have the best effect,and the oviposition inhibition rates after 72 h treatment at 10μL/m L are as high as 98.59%and 94.37%respectively.Citronellol and geraniol also had some inhibitory effects,and the oviposition inhibition rate was over 85%after 72 h treatment with 15μL/m L concentration.Citronellal and benzyl alcohol have poor oviposition inhibition effects,and the oviposition inhibition rate can reach above 85%when the concentration is 80μL/m L.5)The results of RT-PCR showed that the gene expression levels of vitellogenin receptor,vitellogenin-5-like,vitellogenin-6-like,vitellogenin-3,vitellogenin-1 and vitellogenin-4-like were significantly down-regulated compared with the control after the treatment of female adults T.urticae with LC₃₀ concentration of carvacrol.In the eugenol treatment group,the gene expression of vitellogenin receptor,vitellogenin-4-like and vitellogenin-6 was up-regulated,while the gene expression of vitellogenin-3,vitellogenin-6-like and vitellogenin-1 was significantly down-regulated.CYP392A6,CYP392A16,CYP392A11,and CYP392A3 expressions were down-regulated in both treatment groups.CYP392A12 gene expression was up-regulated in both treatment groups.CYP392A2p gene expression was significantly reduced under eugenol treatment and slightly increased under carvacrol treatment.CYP392A14 gene expression was slightly up-regulated by eugenol and down-regulated by carvacrol.In this study,the acaricidal activity and oviposition inhibitory activity of plant essential oil and its main components were compared,and four potential compounds with biological activity were screened out,which are respectively carvacrol,eugenol,citronellol and geraniol,which provided the theoretical basis for the development of botanical pesticides against T.urticae.