Preparation And Bio-safety Evaluation Of Internally-adsorbed Translocation Spinosad Nano-controlled Release Agent

Zea mays L（Corn）is the most important cereal crop of China and plays an important role in the country’s food security.The Asian corn borer（Ostrinia furnacalis（Guenee））,a tunneling pest,is one of the major factors affecting corn growth and yield.To efficiently control the O.furnacalis,this study prepared mesoporous silica nanoparticles（MSNs）using a sol-gel method,modified MSNs using APTES,coated them with an alkaline-sensitive material,polylactic acid,and loaded them with spinosad to form a core-shell structure,constructing a p H-responsive nanoscale insecticide that targets the pest’s gut microenvironment.The physicochemical properties of the nanoparticles were characterized using FTIR,UV-vis,Zeta potential,TEM,BET,TGA,and particle size analysis.The release properties and photostability of the loaded nanoparticles,as well as their biological activity against O.furnacalis larvae and their translocation in corn plants,were investigated,and their safety for non-target organisms was evaluated.The specific research findings are as follows:（1）Amino-functionalized mesoporous silica（MSNs-NH₂）and spinosad@MSNs-PLA were successfully synthesized by the sol-gel method and surface modification.The results of scanning electron microscopy（SEM）and transmission electron microscopy（TEM）showed that MSNs-NH₂were regular spherical particles with an obvious mesoporous structure,allowing for absorption and transportation by corn as a carrier.The surface of spinosad@MSNs-PLA is rough,with a particle size of about 80 nm,and the outermost layer has a white shell.The alkali-sensitive polymer is attached to the surface of the aminated silica,forming a certain core-shell structure.The results of FTIR,UV-vis,BET,and Zeta potential also indicated the successful grafting of the alkali-sensitive substance polylactic acid and the successful loading of spinosad.Furthermore,the results of centrifugation showed a high loading rate of spinosad@MSNs-PLA,reaching 38.6%.（2）The release kinetics of spinosad@MSNs-PLA and the release behavior of spinosad under different p H conditions were studied.The results revealed that spinosad@MSNs-PLA only exhibited trace amounts of spinosad detection at p H 5.0 and7.0 on the 7th day.However,the cumulative release rates of spinosad at p H 9.0 and 10.0reached 42.79%and 46.36%,respectively.These findings indicate that the nano-preparation can only be released under alkaline conditions and has limited release under acidic or neutral conditions.（3）The photolysis rates of spinosad technique and spinosad@MSNs-PLA were measured under artificial simulated UV irradiation.The spinosad technique exhibited rapid light attenuation,with a loss of active components reaching 92.7%after 10 hours of UV irradiation.In contrast,the decomposition rate of spinosad@MSNs-PLA reached 11.3%after 24 hours of UV irradiation.（4）The bioactivity of spinosad EW,blank MSNs-NH₂,and spinosad@MSNs-PLA against the third instar corn borer was determined using the artificial feed film method.The results demonstrated that after 24 hours of treatment,the third instar corn borer fed with blank MSNs-NH₂showed almost no mortality.However,when comparing groups with the same content of active ingredients,the insecticidal activity of the third instar corn borer treated with spinosad@MSNs-PLA was higher than that of spinosad EW.（5）The transport and distribution of spinosad@MSNs-PLA on maize leaves were assessed using laser confocal microscopy and the molybdenum blue method,respectively.The results demonstrated that the riboflavin-labeled spinosad@MSNs-PLA was transferred from the upper leaves of the treated maize to the lower leaves.The silicon content in the lower leaves was 0.110 mg,while the blank control had a silicon content of only 0.024 mg.These findings indicate that spinosad@MSNs-PLA can be absorbed and transported more effectively in maize compared to traditional spinosad emulsion pesticides.（6）Safety tests were conducted to evaluate the effects of spinosad EW and spinosad@MSNs-PLA.The results revealed that the 24-hour LC₅₀of spinosad@MSNs-PLA to zebrafish was 4.556 mg/L,whereas the 24-hour LC₅₀of spinosad EW was 244.340 mg/L.The 24-hour LC₅₀of spinosad@MSNs-PLA was more than 50times higher than that of spinosad EW.In terms of maize safety,spraying spinosad EW resulted in phytotoxicity and lower growth indexes compared to spinosad@MSNs-PLA.Conversely,spraying spinosad@MSNs-PLA had no significant negative effect on maize growth and development.Therefore,the prepared spinosad@MSNs-PLA has great application potential in the field of agricultural production.In addition,the constructed internally conductive stimulus-responsive release carrier can improve the utilization rate of pesticides and reduce environmental pollution.This study provides new ideas for the efficient control of other boring pests.