Extraction optimization of insecticidal compounds from Lysurus mokusin by response surface methodology

We optimized the extraction process of Lysurus mokusin(L.)Fr.insecticidal compound(LMIC)using response surface methodology with ultrasonic extraction(UE).The surface morphologies of maceration extract(ME)and UE residues were compared by scanning electron microscopy,and then the activity of LMIC on Lymantria dispar(Asian gypsy moths)larvae was determined.Results showed that the optimal condition of UE was followed by 80 min of extraction time,60%of ethanol concentration and 80 mL g^-1 of liquid–solid ratio.The surface morphologies of UE residue were looser and rougher than ME residue.The corrected mortalities of LMIC on L.dispar larvae was 59.77%.This result indicated that L.mokusin was a good candidate as pesticide for pest management.

Larvicidal activity and microencapsulation of tobacco(Nicotiana tabacum)extract on Malacosoma neustria testacea larvae

To understand and improve the stability of the insecticidal activity of tobacco extract,the 3 rd instar larvae of Malacosoma neustria testacea was determined by the leaf film method.Spectrophotometry identified extract effects on activities of several enzymes.In addition,to improve the stability of the extract,microcapsules were prepared by complex coacervation and phase separation with the extract as core material,and gelatin and gum arabic as wall material.With the embedding rate as the evaluation index,the response surface method was used to optimize the preparation process of the microcapsules.The results show that the extract had a strong insecticidal activity on the larvae,with inhibitory effects on several enzymes examined of carboxylesterase,acetylcholinesterase,glutathione-S transferase,catalase,and superoxide dismutase.The inhibition rate increased with time.The best preparation process of tobacco extract microcapsules was 25% mass fraction of emulsifier,2.05% mass fraction of gelatin,3% mass fraction of gum arabic,1.34 wall core ratio,36 min of complex coacervation time.The embedding rate was 58.4% which is approximately the theoretical embedding rate(58.9%).The microcapsules prepared by this method have a smooth surface,good combining form and particle size distribution,and a median diameter of 8.6 μm.Infrared characteristic peaks of the extracts were preserved at 877.55 cm^(-1) and2922.13 cm^(-1).Microencapsulation can improve the thermal stability of the tobacco extract.Indoor toxicity tests showed that LC_(50) of extract microcapsules was 20.2 mg·mL^(-1),equivalent to the toxicity level of the tobacco extract itself,indicating that microencapsulation did not reduce extract insecticidal effects.This research may provide a reference for the optimization of the tobacco extract microcapsule preparation process.

Molecular cloning, characterization, and antioxidant function of catalase in Lymantria dispar asiatic (Lepidoptera: Lymantriidae) under avermectin stress

The critical antioxidant catalase(CAT)breaks down hydrogen peroxide induced by environmental stresses.Here we cloned full length catalase cDNA from Lymantria dispar asiatic(LdCAT).Bioinformatic analyses showed that open reading frames of LdCAT contains 1524 bp,encoding 507 amino acids with molecular weight of 126.99 kDa,theoretical pI of 5.00,aliphatic index of 29.92,grand average of hydropathicity of 0.764,and instability index(II)of 46.56.Protein BLAST and multiple sequence alignment indicated that LdCAT had high identity with CAT from other insects,especially lepidopterans.In a phylogenetic analysis,LdCAT was most similar to CAT from Spodoptera litura and S.exigua.Quantitative realtime polymerase chain reaction showed that LdCAT transcripts in all instar larvae and the five tissues tested,verifying the ubiquity of LdCAT in L.disapr.Moreover,LdCAT of third instar larvae was significantly upregulated after they fed on avermectin at sublethal and LC10 doses.The highest relative transcript levels were found 2 h after an avermectin spray at LC90,and in the cuticula,rather than heads,fat bodies,malpighian tubes,and midguts after a spray avermectin at a sublethal concentration.The expression level of LdCAT under pesticide stresses here suggested that CAT is an important antioxidant enzyme of L.disapr defensing against pesticide stress and may be a good target for controlling this pest.

Stress response of Lymantria dispar asiatica(Lepidoptera:Erebidae)larvae and its gut microbiota to manganese ion

To study the effect of manganese exposure on the herbivorous insect Lymantria dispar asiatica,fourthinstar larvae were fed a MnCl_(2)-amended diet(LdMn)for 84 h(0.40 mmol MnCl_(2)/g diet).Larvae were weighed before and after the diet administration to assess larval gain in mass under manganese exposure.The whole bodies of half of the survivors were ground in liquid nitrogen for measuring enzyme activities and total antioxidant capacity(T-AOC).The intestinal tracts of the remaining survivors were collected and immediately frozen in liquid nitrogen for 16S rDNA sequencing of gut microbiota.Larvae under manganese stress lost significant mass(p<0.05).The activities of digestive and antioxidant enzymes and T-AOC,but not trehalase and polyphenol oxidase,were significantly higher after Mn exposure,(p<0.05).A Venn diagram illustrated that the gut microbial OTU composition in the larvae also changed.Community pies and correlation heatmaps also showed different relative abundances of gut microbes.In other words,species quantity and relative abundance of gut microbes agreed with PCoA visualization and indicated that the gut microbial community in L.dispar asiatica larvae differed significantly between control and LdMn.Functional classification also suggested that exposure to manganese stress significantly decreased gut microbial coenzyme transport and metabolism in L.dispar asiatica larvae.These results further our understanding about stress response of L.dispar asiatica larvae.