Preparation Characterization Of Nanochitin And The Insecticidal Activity Against Wheat Aphids

Chitin,as a natural polymer with positive charge,is available in quantity from the shells of marine crustaceans sunch as crabs,shrimps,fungal and yeast cell walls,in krill,lobster and insect cuticle,having unique structure,multidimensional properties(such as biodegradability,biocompatibility,non-toxicity and adsorption),highly sophisticated functions and wide ranging applications in biomedical and other areas.The polymer of which is β-(1-4)-N-acetyl-D-glucosamine,chitin is considered to be materials of great futuristic potential with immense possibilities for structural modifications to impart properties and functions,research and development.When the degree of deacetylation of chitin reachs about 50%,it become soluble in aqueous acidic media and is called chitosan.chitin has a status of intense activities in many parts of the world.In fact,as in case of cellulose,chtin exists in three different polymorphic forms(α,β and γ).This molecule has been shown to display toxicity and inhibit fungal growth and development,applied to the plant protection from diseases,insect control,the regulation of plant and other areas in agriculture.The biological activity of chitin/chitosan belongs to the-NH2,polycation effect is also caused by the perssad.The key to solve the issue that enhancing insecticidal activity for chitin usually deponds on chelating with metal cations and increasing the active base to chitin.As a result,chitin derivatives show distinct insecticisdal activity such as active against viruses,bacterial,pests in Noctuidate(Spodoptera mauritia and Helicoverpa armigera Hubner),Plutellidae(Plutella xylosteella),Aphididae(Aphis gossypii Glover and Myzus persicae).But no research has been reported abou wheat aphids till now.This research paied attentionon the insecticidal activity of chitin,in another pathway,preparating chitin to nano particles,minimizing the size,increasing the charge density,improving the ionic effect.Nano materials has drawn enoughattentions for the special physical properties,specific surface area,the ability of adsorbing metal cations and nonmetal cations and so on.New theories,techniques,methods for pest control and the development will be emerged under the incorporation of nano science and agriculture.This research mainly focused on the preparation and characterization of nanochitin and the toxicity of nanochitin against wheat aphids.To investigate the effectiveness of nanochitin,chemistry reaction,instrumental analysis,biological assay,enzyme activity analysis methods were used for the agricultural pest control and the development of nano matetial pesticides.The main findings are as follows:(1)The insecticidal activity of chitin was improved by using chitin nanoparticles.α-chitin,as the most abundant natural aminopolysaccharide with atable structure,could be the main material used for the synthesis of nanochitin containing homogeneous particles.For which method the reduction of cost and facilitation of the key processing process could be realized.(2)The acid cracking method was adopted to prepare for nanochitin.The most suitable procedure for the preparation of nanochitin was as follow: nanochitin was prepared by the acid hydrolysisi of chitin powder with 3N HCl at 80 ~ 85℃ for 1.5 h× 3times under vigorous stirring,the ratio of HCl to chitin powder was 200 ~ 300 m L/g.After acid hydrolysis,the obtained nanochitin suspensions were diluted with distilled water and were then centrifuged at 9 000 rpm for 15 min and decanted in triplicate.The suspensions were the transferred to dialysis bags and dialyzed in distilled water for 5 ~ 7 d under vigorous stirring till the p H was about 6.0.(3)Characterization of nanochitin was detected comprehensively.According to the results of characterization,the as-prepared nanochitin particles were present as slender rods with sharp point on both ends.The effective diameter of these rods were144.74 ~ 346.8nm,The effective diameter of 95% particles were 0 ~ 219.3 nm,the zeta potential of the nano whiskers were 13.89 ± 2.77~ 36.08 ± 2.26 m V,the charge density of nanochitins were 13.5935×10-5~ 46.1916×10-5 mol/g.(4)Toxicity test of nanochitin against 3 kinds of wheat aphids was investigated.The results showed that the LC50 of NCs to M.avenae,S.graminum,and R.padi were17.825,20.589 and 14.381 mg/L,respectively(the effective diameter of these rods were 157.0 nm,the charge density of nanochitins were 46.1916×10-5 mol/g).The simulated field study on the efficacy showed that NCs had a great capability in wheat aphid control with the decresae rate of 80.33%,79.65% and 82.57% respectively for M.avenae,S.Graminum,and R.Padi at the concentration of 40 mg/L.(5)The lethalities of mixture of NCs-imidacloprid(1:1 mixture by volume)to the tested aphids were 88.31%,87.21% and 84.76% respectively for the simulated field study lasted for 7 days(the effective diameter of these rods were 157.0 nm,the charge density of nanochitins were 46.1916×10-5 mol/g).(6)Spectrophotometric method was utilized to record of the activity of acetylch--line sterase(ACh E)in 3 wheat aphids after treated with NC,showing different results for 3 kind saphids.The activity of acetylchline sterase in aphids after treated by nanochitin had a significant decrease in Rhopalosiphum padi at 12 h,24 h and 48 h,but there was no significant influence on Macrosiphum avenae or Schizaphis graminum.