Preparation Of Abamectin Loaded On Dendritic Silica Nanoparticles And Its Toxicity To Monochamus Alternatus

Monochamus alternatus is an important resident pest that endangers many economic and ecological forests such as Pinus massoniana,Pinus thunbergii and Pinus densiflora,and it is also the main vector insect of Bursaphelenchus xylophilus.The rapid spread of Monochamus alternatus not only affects the growth and development of trees,but also brings direct economic losses and ecological service value losses to China.At present,Monochamus alternatus is mainly controlled by chemical methods.As an efficient and broad-spectrum insecticide,abamectin has the characteristics of photodegradation,poor water solubility,short duration and environmental pollution caused by excessive use,which severely limits its application in pest control.In view of the above problems,this study designed and prepared a nano drug delivery system with UV-resistant degradation performance and slow release by using dendritic mesoporous silica as the nanocarrier and neuroinhibitor abamectin as the model drug,and determined its toxicity.The specific results are as follows:1.Dendritic mesoporous silica nanoparticles（DMSNs）were synthesized by one-pot method using cetyltrimethylammonium bromide（CTAB）and sodium salicylate（NaSal）as structure-directing agents,tetraethyl orthosilicate（TEOS）as silicon source,triethylamine（TEA）as catalyst,and abamectin was loaded on purified DMSNs to prepare nanobiopesticides.The morphology of DMSNs was characterized by field emission scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.The results showed that DMSNs were dendritic mesoporous structure with uniform dispersion.The particle size was about 250 nm,and the drug loading rate was as high as 68.8%.2.The slow-release performance was evaluated by studying the degradation performance of nano-pesticides.The results showed that DMSNs at different pH values had been mostly degraded in about 28 days.In the corresponding release experiment,the release amount reached more than 90%at 28 days,and the slow-release was accompanied by carrier degradation.In addition,the photodegradation evaluation of abamectin by UV lamp showed that DMSNs had obvious photoprotective effect on abamectin.The abamectin loaded by DMSNs was only degraded by 23.3%after 84 h of light irradiation,while the original drug had been degraded by 72%.3.The fluorescence distribution of DMSNs-AVMNPs on the surface and intestine of Monochamus alternatus larvae was studied.The results showed that DMSNs-AVMNPs could be evenly distributed to the body wall and stomata of Monochamus alternatus larvae,and also could effectively transfer abamectin to the intestinal tract of larvae and be absorbed by larvae.This indicated that DMSNs-AVMNPs might produce toxicity through exposure and feeding,and improve its utilization rate.4.The indoor contact toxicity and stomach toxicity evaluation were carried out for the trunk borer Monochamus alternatus.The indoor biological activity test was carried out with abamectin and emulsifiable concentrate as the control agents.The results showed that DMSNs-AVMNPs had long duration of efficacy and stable efficacy,although the initial efficacy was not as good as that of the original drug.The LC₅₀of stomach toxicity and contact toxicity was slightly higher than that of the original drug.The LC₅₀of contact toxicity to larvae was 14.27μg/mL at 96 h,and the LC₅₀of stomach toxicity was 10.90μg/mL.5.The experiment of self-flow injection of DMSNs-AVMNPs showed that the absorption rate of DMSNs-AVMNPs was higher than that of abamectin and emulsifiable concentrate,and in a certain concentration range,the transmission rate of nano-agents with lower concentration was faster.In summary,the dendritic mesoporous silica nano-release system loaded with abamectin prepared in this paper can effectively prevent the photolysis of abamectin and has good sustained-release performance,which can provide reference and basis for the prevention and control of Monochamus alternatus.