Study On The Biological Activity Of Sapindus Saponins Against Spodoptera Exigua And Its Chemical Constituents

Sapindus saponaria is a deciduous tree of Sapindus of Sapindaceae,and is an economic tree species with high comprehensive utilization value.Its arils contain a large amount of saponins.At present,there have been reports on the antibacterial,antitumor,cardiovascular and cerebrovascular protection,and insecticidal studies of Sapindus saponins.In view of this,in this paper,Sapindus saponins was used as the material,and Sapindus saponins were extracted by water extraction method.Spodoptera exigua larvae were fed with mixed feed treated with sapindus saponin,and various indicators related to the growth,development and reproduction of the Spodoptera exigua larvae were measured,and the effect of sapindus saponins on the detoxification enzymes of Spodoptera exigua was discussed.The main chemical constituents of Sapindus saponins were qualitatively analyzed by liquid chromatography-mass spectrometry(HPLC-MS).The purpose is to provide theoretical basis and scientific guidance for the development of Sapindus saponins into low-toxic and efficient botanical pesticides.The main research results are as follows:1.Insecticidal activity of Sapindus saponins against Spodoptera exigua enhanced.Sapindus saponins had better gastric toxicity to the 4th instar larvae of Spodoptera exigua than the 2nd and 3rd instar larvae.On the 6th day after the treatment,the mixed feed of 16 mg/g had better control effect on the 4th instar larvae of Spodoptera exigua.The corrected mortality rate was 76.67%;the contact killing effect of sapindus saponins on the 2nd and 3rd instar larvae of Spodoptera exigua was better than that of the 4th instar larvae.On the 1st day after the treatment 64 mg/mL sapindus saponin was effective against the 3rd instar larvae of Spodoptera exigua.The control effect of larvae was better,and the corrected mortality was 43.33%.2.Effects of Sapindus saponins on the growth,development and reproduction of Spodoptera exigua:Sapindus saponins have different effects on the growth,development and reproduction of the 2nd,3rd and 4th instar larvae of Spodoptera exigua.First of all,Sapindus saponins can reduce the pupation rate and egg hatching rate of Spodoptera exigua larvae.The pupation rate of the second instar larvae of Spodoptera exigua under 4mg/g mixed feed treatment was reduced by 46.43%compared with the blank control group.Compared with the blank group,the pupation rates of the 3rd and 4th instar larvae of Spodoptera exigua under the treatment of 8 mg/g poisonous feed were reduced by 89.29%and 74.04%respectively;Compared with the blank control group,the egg hatching rate decreased by 16.12%,and the egg hatching rate of the third instar larvae of Spodoptera exigua under 4 mg/g mixed feed treatment decreased by 28.55%compared with the blank control group.The developmental period of moths,the larval stage of the 2nd instar larvae under the 4 mg/g mixed feed treatment was prolonged by 8.55 d compared with the blank control group,and the 3rd and 4th instar larvae of Spodoptera exigua under the 8 mg/g mixed feed treatment.Compared with the blank control group,the larval stage was prolonged by 3.88 d and 5.64 d,respectively.In addition,Sapindus saponins could also reduce the body weight and pupa weight of Spodoptera exigua.Compared with the blank control group,the body weights of the 2nd,3rd and 4th instar larvae were reduced by 79.65%,71.83%and 82.93%respectively;the pupa weight of the 2nd instar larvae treated with 4 mg/g mixed-toxic feed was reduced by 41.13%compared with the blank control group,the pupa weights of the 3rd and 4th instar larvae of Spodoptera exigua were reduced by 57.25%and 83.65%under the 8 mg/g mixed feed treatment compared with the blank control group,respectively;Sapindus saponin had a certain effect on the female ratio of Spodoptera exigua,but not significantly different from the blank control group.3.Effects of different concentrations of Sapindus saponins on detoxification and metabolic enzymes activities of Spodoptera exigua:Sapindus saponins have certain inhibitory effects on GSTs,AChE and CarE in the third instar larvae of Spodoptera exigua.At 24 h after the drug,when the concentration of the drug was 64 mg/mL,the inhibitory effect on GSTs was obvious,and the enzyme activity was 0.67 times that of the blank control group;at 48 h after the drug,when the concentration of the drug was 64 mg/mL,the inhibitory effect on AChE was obvious,and the enzyme activity was 0.56 times that of the blank control group at the same period;at 72 h after the drug,when the concentration of the drug was 32 mg/mL and 64 mg/mL,the inhibitory effect on CarE was obvious,and the enzyme activities were 0.81 and 0.79 times that of the blank control group during the same period;this result reflects the cause of death of Spodoptera exigua after exposure to Sapindus saponin,and also indicates that detoxification metabolic enzymes are involved in the test insect’s defense mechanism against Sapindus saponin.4.Chemical composition analysis of Sapindus saponin:The saponins in the peel of Sapindus saponaria were identified by HPLC-MS.A total of 43 saponins were identified in this study,of which 20 main saponins have been identified.The structural formula and molecular formula of the other 23 saponins were only identified by molecular formula.The above 20 kinds of saponins include 14 kinds of triterpenoid saponins and 6 kinds of sesquiterpene saponins in total,and triterpenoid saponins and sesquiterpene saponins account for 70%and 30%respectively.