Study On The Control Effect Of D-limonene Against Bemisia Tabaci And Its Fate In Tomato And Soil

D-Limonene is a cyclic monoterpene that is abundantly present in a diverse range of essential oils,notably lemon oil,wormwood oil,orange oil,bergamot oil,and dill oil.It possesses notable insecticidal,antimicrobial,and herbicidal properties.Based on the efficacy of a 5%soluble solution of D-limonene against Bemisia tabaci（Gennadius）in tomatoes,this study established a constant and residual analysis method for D-limonene and investigated the environmental behavior of D-limonene and its oxidation products in tomatoes and soils.Following were the results:（1）A field experiment was conducted to investigate the effectiveness of a 5%soluble solution of D-limonene in controlling B.tabaci in tomato plants and its impact on tomato yield.The results revealed that the 5%D-limonene soluble solution at a dosage of 50-100 g a.i./ha exhibited a pest control efficacy ranging from 76.6%to 88.0%against B.tabaci 7days after application and resulted in a significant increase in tomato yield ranging from48.72%to 66.47%,which was superior to the control treatment with 1000 g a.i./ha of 99%petroleum spray oil and 66.7 g a.i./ha of 1.3%matrine aqueous solution,and comparable to the control treatment with 30 g a.i./ha of 5%imidacloprid wettable powder.Thus,the 5%D-limonene soluble solution is suitable for the control of B.tabaci in tomato plants and is recommended for application at a dosage of 75-100 g a.i./ha in the field.（2）A method for determining the content of active ingredients in D-limonene formulations was developed using gas chromatography-mass spectrometry（GC-MS）.D-limonene content was determined using external standard method through SIM mode with HP-5MS capillary column as separation column,N-hexane as solvent and helium as carrier gas.Linear independence of the method was 0.9996,RSDs were 2.2-4.0%,and the recoveries were 96.5-102.6%.The method is simple,accurate and reproducible,which is an ideal method for the determination of D-limonene.（3）A rapid,efficient,and convenient method for detecting the residue levels of D-limonene and its oxidation products in vegetables and soils was established using GC-MS.The quick,easy,cheap,effective,rugged,and safe（Qu ECh ERS）method was used to extract the samples using n-hexane,followed by purification with C₁₈ and GCB,and detection by GC-MS.The linear correlation coefficients of all analytes in the nine matrices were good（R²>0.995）.At levels of 50,100,and 1000μg kg^-1,the average recoveries ranged from 71.2to 114.5%,while intra-day and inter-day precision were below 13.4%.The limits of detection（LODs）and the limits of quantification（LOQs）in all matrices for D-limonene and its five oxidation products were 1-16 and 4-48μg kg^-1,respectively.The residual levels of D-limonene can be well described by first-order kinetics.Dissipation in soil was microbially dominated and its oxidation products were converted in soil mainly by microorganisms,with trans-isomers being more abundant than cis-isomers.Furthermore,no traces of D-limonene or its oxidation products were found in tomatoes,indicating the absence of residues.Additionally,D-limonene exhibited a relatively short persistence in soil.（4）The degradation behavior of D-limonene in five types of soil was simulated in indoor experiments.The results showed that the degradation of D-limonene in five soils fitted the first-order kinetic equation,and the main factors affecting D-limonene degradation in soil were microorganisms,p H,temperature,and soil moisture content.Aerobic microbial degradation was the main pathway for D-limonene degradation in soil,and degradation rate was significantly increased in alkaline soils and high-temperature environments.The degradation rate of D-limonene was significantly accelerated in alkaline soil and high-temperature environments.As soil moisture content increased,the degradation rate of D-limonene also increased.However,excessively high soil moisture content（120%W/W）inhibited the degradation of D-limonene,and the addition of humic acid and biochar reduced the degradation rate of D-limonene.The degradation of D-limonene in soil is influenced by multiple factors,and the research results contribute to understanding the behavior of D-limonene in soil and laying the foundation for further study of its applicability as an environmentally friendly pesticide.