Research On Fumigant Activity And Mechanism Of Schizonepeta Tenuifolia Against Cryptolestes Ferrugineus

The rusty grain beetle（Cryptolestus ferrugineus）（Coleoptera:Laemophloeidae）is a globally common stored grain pest.In addition to directly feeding on stored grain,the rusty grain beetle can easily cause serious damage to grain storage and quality,such as heat and mold in the grain pile.The purpose of this study is to investigate the fumigation activity and insecticidal mechanism of Schizonepeta tenuifolia Briq.on C.ferrugineus.In this study,we measured the fumigation activity of S.tenuifolia spike（SS）powder and volatile eluents against adults and larvae of C.ferrugineus,respectively;analyzed the main components of the SS volatile eluents by GC-MS.The effects of SS volatile eluents on the activities of acetylcholinesterase（ACh E）,glutathione S-transferase（GSTs）,carboxylesterase（Car E）,peroxidase（POD）and superoxide dismutase（SOD）of C.ferrugineus adults were determined.The main results of the study are as follows:1.The repellent and fumigant activity of SS powder against C.ferrugineus were measured.The results showed that the SS powder had good repellent and fumigant activity against the adults,and the mortality rate of C.ferrugineus increased gradually with the increasing dosage.Compared the fumigation effect of SS volatiles extracted with different adsorbents and flow rates,it was found that the volatile eluents extracted by the Porapak?Q adsorbent at a flow rate of 600 m L/min had a 78.89%mortality rate on C.ferrugineus adults at 24 h,and a mortality rate of 91.11%at 48 h.2.We analyzed the effects of factors such as different districts and temperatures on the fumigation activity of S.tenuifolia.It was found that the fumigation activity of SS volatile eluents from Anhui,Jiangsu,and Yunnan were significantly higher than from Zhejiang and Hebei within 4-12 h.However,there was no significant difference in fumigation activity between the five producing areas at 24 h.Subsequently,S.tenuifolia from Anhui province was used for experiments,and it found that the LC₅₀ of10.25μL/L and 68.64μL/L for adults and larvae of C.ferrugineus at 24 h,respectively.In addition,the SS volatile eluents also showed insecticidal activity against four other stored grain pests.After 48 hours of fumigation,the mortality rate of Sitophilus oryzae was consistent with that of C.ferrugineus,both reached 100.00%,while the mortality rates of Oryzaephilus surinamensis,Lasioderma serricorne and Tribolium castaneum were 96.67%,32.22%and 21.11%,respectively.At relatively low temperatures,the insecticidal effect of SS volatile eluents was significantly enhanced.After 4 h,the mortality rate of C.ferrugineus adults reached 100%at 15℃.Moreover,SS volatile eluents had good fumigation effect against adults of C.ferrugineus of different ages,and there was no significant difference in its fumigation effect.3.GC-MS was used to analyze the components of the SS volatile eluents.The results showed that there were ten main components in the SS volatile eluents,and the top four with the highest peak area proportion were pulegone（62.62%）,isomentone（18.34%）,2-isopropyl-2,5-dimethylcyclohexanone（2.45%）,and isopulegone（1.32%）.The toxicity test results of pulegone and isomentone showed that only pulegone had insecticidal activity,with a LC₅₀ of 12.62 m L/L and 29.38 m L/L for adults and larvae of C.ferrugineus,respectively.The temperature measurement results of pulegone were consistent with the volatile eluents,and the fumigation effect on C.ferrugineus adults at 15℃was significantly higher than that at 30℃.4.In order to further investigate the mechanism of SS volatile eluents on C.ferrugineus,the activities of five enzymes,including ACh E,Car E,GSTs,POD and SOD,were measured.The results showed that SS volatile eluents and pulegone significantly inhibited the Car E activity of the C.ferrugineus at four time points,and their inhibition rates of Car E in vivo reached 84.87%and 63.82%,respectively.However,the SS volatile eluents and pulegone significantly inhibited the activities of ACh E,POD and SOD only at 24 h,but had no significant effect on the activity of GSTs.In summary,this thesis confirmed that SS had a good repellent and insecticidal activity against the stored grain pest C.ferrugineus,and its insecticidal activity increased significantly when the volatile eluents was extracted at lower temperatures.Furthermore,GC-MS analysis identified pulegone as the main insecticidal component.The SS volatile eluents and pulegone can significantly inhibited the Car E activity of C.ferrugineus,and also had a certain effect on the protective enzymes SOD and POD.