| Chemical pesticides play a leading role in forest pest control,whose long-term use in large quantities can cause forest pests to develop drug resistance,serious environmental pollution and other problems.Therefore,the development of new biological pesticides instead of chemical pesticides has become an inevitable trend in the pesticide industrial development.Insecticidal plant resources are abundant in nature,which can provide a sufficient source of raw materials for the development of plant-based pesticides.The insecticidal active ingredients in plant-derived pesticides have attracted widespread attention due to their advantages such as natural degradation,low toxicity,and no residue.In the present study,the active substances of toxic plants endemic to the north were used to screen out two insecticidal biological activity plants of Nicotiana tabacum and A conitum kusnezoffii.Then we optimized the extraction process of two plant active substances and analyzed the biological active ingredients of the two plant extracts.After that,the mechanism of action of two plant extracts on enzymatic activity in Lymantria dispar were studied,and the effects of main active ingredients on intestinal microorganisms of Lymantria dispar and Dendrolimus superans were measured.Finally,the preparation processes of the two plant extract microcapsules were optimized respectively,and the biological safety of both extracts and microcapsules were evaluated.The present study can provide a technical support for the development,preparations and applications in forest pest control of plant-derived pesticides containing Nicotiana labacum.and Aconitum kusnezoffii.The main results are as follows:(1)The optimal extraction method for the test insecticidal plant extract was ultrasonic extraction,and the optimal extraction solvent was methanol.The insecticidal activity of Nicotiana tabacum and Aconitum kusnezoffii extract was significantly better than that of other 14 plants.The optimum extraction conditions for extract from Nicotiana tabacum were:51.13?,liquid-to-material ratio 32.25:1,40.19 min,and the extraction rate was 39.36%.And the optimum extraction process parameters for extract from Aconitum kusnezoffii were:52.16?,liquid-to-material ratio 31.15:1,40.72 min,and the extraction rate was 23.85%.(2)The corrected mortality rates of the ethyl acetate extracts of Nicotiana tabacun and Aconitum kushezoffii on 3rd instar Lymantria dispar larvae were 58.62%and 48.28%,respectively,and the insecticidal activity was significantly different from other extracts.LC-MS analysis of Nicotiana tabacum extract showed that nicotine,quercetin and coumarin were the main insecticidal active ingredients.GC-MS analysis of Nicotiana tabacum extract showed that butyl butyrate,diisobutyl phthalate and 4-hydroxy-?-dihydrodamonone were the main insecticidal active ingredients.LC-MS analysis of Aconitum kusnezoffii extract showed that aconitine,hypoconicine and neoaconitine were the main insecticidal active ingredients.GC-MS analysis of Aconitum kunezoffii extract showed that pentadecanoic acid,n-octyl phthalate and dioctyl adipate were the main insecticidal active ingredients.(3)Both Nicoliana tabacum and A conitum kusnezoffii ethyl acetate extract were neurotoxic to L.di.spar larvae.Insecticidal substances such as nicotine and aconitine alkaloids can reduce the detoxification function of Lymantria dispar by inhibiting,carboxylesterase(CarE)activities.At the same time,the two agents inhibited the protective function of the body by inhibiting the activities of epidermal superoxide dismutase(SOD)and fat body catalase(CAT).And they inhibited the lipase(LPS)and amylase(AMS)activities in the fat body of Lymantria dispar,reduced the ability of the body to provide nutrients to inhibit its growth and development.Thus the two agents can be used as insect nerve poisons and digestive enzyme inhibitors.(4)When nicotine treated the 4rd instar larvae of Dendrorimus superans,the abundance of Enterococcus in the intestine decreased significantly,which reduced immunity and inhibited their growth and development until death.After treated with nicotine,65.85%OTU of the bacteria in the intestine were significantiy different from the control(P<0.05).nicotine affected the function of coenzyme transportation and decomposition of byproducts of the intestinal microorganisms and inhibited the production of toxic enzymes and the ability to metabolize toxicants,thereby causing toxic damage to the body of Lymantria dispar.After treated with nicotine,43.24%OTU of the bacteria in the intestine were significantly different from the control(P<0.05),nicotine affected the structure and function of intestinal microbial cells,reduced the energy storage capacity of the cell and inhibited the growth of Dendrolimus superans.In the 4rd instar larva of Lymantria dispar treated with aconitine,73.17%OTU of the bacteria in the intestine were significantly different from the control(P<0.05).Therefore,the abundance of Weisseria spp.in the intestine was significantly reduced,which affected the nucleotide transport function of intestinal microorganisms,inhibited the synthesis of ecdysone and reduced the production of body proteins,thus affecting the growth of Lymantria dispar.In the 4rd instar larva of Dendrolimus superans treated with aconitine,24.32%OTU of the bacteria in the intestine were significantly different from the control(P<0.05),Therefore,the abundance of Wolbachia in the intestine was significantly reduced,which affected the lipid transport function of intestinal microorganisms,inhibited ATP synthesis function,hindered the energy supply,and thus inhibited the growth and development of Dendrolinus superans.(5)The optimal preparation conditions of Nicotiana tabacum extract microcapsules were:chitosan mass fraction 0.31%,core-to-wall ratio 1:1.04,48.10 min and that of Aconitum kusnezoffii extract microcapsules were:chitosan mass fraction 0.30%,core-to-wall ratio 1:1.06,48.20 min.Under the optimal preparation conditions,the actual measured embedding rates were 45.98%and 42.89%,respectively,and the relative errors from the predicted values were less than 1%,indicating that the optimization process is reasonable and feasible.Nicotiana tabacum extract and Aconitum kusnezoffii extract microcapsules had significant weight loss temperatures of 129.96? and 148.20?,respectively,and were stable at room temperature.Release of capsule core was 6 days longer than that of extract,and slow-release performance of microcapsules was significantly improved.The LC90 values of the two microcapsules against Lymantria dispar were 18.363 mg/mL and 35.831 mg/mL,respectively,which were significantly lower than those of extracts.(6)The two extracts had inhibitory effects on weight gain and liver protein content in mice.The recoverability of Nicotiana tabacum and Aconitum kusnezoffii extracts on CarE and GSTs activities in mouse liver were better than DDVP.The LD50 of Nicotiana tabacum and Aconitum kusnezoffii extract on Kunming mice were 2269 mg·kg-1 and 3268 mg-kg-1,respectively,showing that they were low-toxic and were safe for humans and domestic animals.Nicotiana tabacum and Aconitum kusnezoffii extract and the corresponding microcapsules had a LC50 of more than 10.0 mg/L for Cyprinus carpio haematopterus.All four agents were low-toxic pesticides and among them two microcapsules were safer for fish than their extracts. |
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