Risk Assessment Of Nilaparvata Lugens (St?l) Resistance To Clothianidin-loaded Mesoporous Organosilica-based Nanosystem

The brown planthopper,Nilaparvata lugens（St?l）,is an important rice pest.Chemical control is the main method to control the brown planthopper.Long-term unreasonable use of chemical pesticides has led to resistance to more than 30 insecticides.Therefore,it is urgent to targeted resistance management strategies,which has the important theoretical significance and application value for ensuring the safe and stable production of rice.Mesoporous organosilica（MON）,as a research hotspot of nanomaterials,has the advantages of large specific surface area,adjustable pore size,uniform pore size,uniform particle size,easy modification of internal and external surfaces and good biocompatibility.It can be used as a nanocarrier of insecticides to improve the bioactivity on target pests.In this study,the important pest of rice,the brown planthopper,was taken as the research object,and its resistance to insecticides was taken as the entry point.The clothianidin@MON nano-drug delivery system was prepared,and its biological activity against brown planthopper and its effect on the development of brown planthopper resistance were explored.The main results are as follows:1.Mesoporous organic silica（MON）was prepared by sol-gel method using tetraethyl orthosilicate（TEOS）and bis-[3-（triethoxysilyl）propyl]-tetrasulfide（BTES）as silicon sources,cetyltrimethylammonium bromide（CTAB）and sodium salicylate（Na Sal）as co-templates.Subsequently,the model drug clothianidin was loaded into MON by solvent evaporation method,and the clothianidin@MON nano-drug delivery system was successfully prepared.The nano drug delivery system was characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,thermogravimetric and differential thermal analysis（TGA-DTA）,Fourier transform infrared spectroscopy（FT-IR）and specific surface area and porosity（BET）.The results showed that the particle size of clothianidin@MON nano-drug delivery system was uniform,about 50 nm,and had good dispersion.Based on high performance liquid chromatography,the loading rate of clothianidin@MON nano-drug delivery system was 8.73%.The toxicity of clothianidin and clothianidin@MON to N.lugens was determined by rice seedling impregnation method.The LC₅₀of clothianidin and clothianidin@MON to N.lugens were 3.41 mg/L and 1.79 mg/L,respectively.The clothianidin@MON nano-drug delivery system significantly improved the toxicity of clothianidin to N.lugens（1.91-fold）.2.The sublethal effects of clothianidin and clothianidin@MON nano-drug delivery system on N.lugens were evaluated based on the bisexual life table.The results showed that compared with the control group,the sublethal concentration of clothianidin and clothianidin@MON nano-drug delivery system had no significant effect on the developmental duration,fecundity and egg hatching rate of F₀adults of N.lugens,and had no significant effect on the developmental duration of F₁eggs,the developmental duration,longevity,total preoviposition period（TPOP）and fecundity of N.lugens.However,the developmental duration,preadult and generation cycle（T）of the 2^ndand 5^thinstar nymphs of the F₁generation of N.lugens were significantly longer than those of the control group,while the developmental duration and preoviposition period（APOP）of the3^rdinstar nymphs were significantly shortened.In addition,compared with the clothianidin treatment group,the developmental duration of the female adults of the F₀generation of N.lugens and the developmental duration of the 2^ndinstar nymphs and female adults of the F₁generation of N.lugens in the clothianidin@MON nano-drug delivery system treatment group were significantly prolonged,while the developmental duration of the 1^stand 4^thinstar nymphs of the F₁generation of N.lugens in the clothianidin@MON nano-drug delivery system treatment group was significantly shorter than that in the clothianidin treatment group.3.The resistance selection of clothianidin and clothianidin@MON nano drug delivery system against brown planthopper was carried out based on rice seedling impregnation method.After 10 consecutive generations of resistance breeding,the resistance ratio of N.lugens to clothianidin reached 32.32-fold(LC₅₀value was 110.20mg/L),and the resistance ratio to clothianidin@MON nano-drug delivery system reached23.04-fold(LC₅₀value was 41.25 mg/L).The resistance development of N.lugens to clothianidin@MON nano-drug delivery system was slower than that of clothianidin.The results of resistance risk assessment showed that the h²of resistance to clothianidin was0.637,and the h²of resistance to clothianidin@MON nano-drug delivery system was0.321.Based on the real heritability of resistance,it was predicted that the generations required for the resistance of N.lugens to clothianidin and clothianidin@MON nano-drug delivery system to produce 10-fold and 100-fold resistance under different selection pressures.The results showed that the resistance of N.lugens to clothianidin@MON nano-drug delivery system was 10-fold and 100-fold longer than that of clothianidin,indicating that mesoporous organic silica（MON）can delay the resistance evolution of N.lugens to clothianidin.