Preliminary Study On The Toxicity And Insecticidal Mechanism Of Ilex Chinensis Essential Oil Against Sitophilus Zeamais

Sitophilus zeamais is one of the harmful stored grain pests.Chemical fumigation is usually used to control the pest species.However,the extensive application of chemical fumigants has led to the increase of insecticide resistance.Therefore,it is of great significance to develop botanical insecticides with high safety and efficiency for the prevention and control of S.zeamais.In this study,we firstly determined the insecticidal activity of six plant essensial oils against S.zeamais,and the best was Ilex chinensis essential oil.Secondly,we identified methyl salicylate as the main active ingredient of I.chinensis essential oil and explored its insecticidal mechanism.We further carried out a series of simulated experiment tests on S.zeamais in wheat storehouse.It provides the preliminary basis for the development of green control products of S.zeamais using methyl salicylate.The results of this study are as follows:1.Insecticidal effect of six plant essential oils on adult S.zeamaisThe fumigation effects of essential oils from six plants,including Chenopodium ambrosioides,Ilex chinensis,Vitex negundo,Litsea cubeba,Perilla seed,and Artemisia vulgaris,on the adults of S.zeamais were determined.The results showed that,after a 24 h treatment with a 20μL/L concentration,I.chinensis essential oil had the best insecticidal effect on S.zeamais（corrected mortality:100%）,follwed with C.ambrosioides essential oil（corrected mortality:71.11%）.The corrected mortality rates of other essential oils ranged from 0%to 15.56%.Considering that the I.chinensis essential oil has the fastest insecticidal speed and better effect,we chose it for further study.2.Chemical composition analysis of I.chinensis essential oilVolatile components of I.chinensis essential oil were analyzed and quantified using GC-MS.Eight components were identified:methyl salicylate,phenol,2-Acetoxyterephthalsaeure dimethyl ester,cinnamyl aldehyde,n-eicosane,eudesmol,n-tetracosane and n-octadecane.The main volatile component was methyl salicylate with a relative content of 98.4%.3.Biological activity of methyl salicylate against S.zeamais adultsThe contact activity of methyl salicylate on adult S.zeamais was determined by insecticide-impregnated filter method.The results showed that the contact effect of methyl salicylate was enhanced with the increase of treatment concentrations and time.At 0.30and 0.35μL/cm²for 48 h,the corrected mortality rates were 94.43%and 98.90%,respectively;and the LD₅₀of methyl salicylate treated for 12,24,36 and 48 h were 0.33,0.28,0.18 and 0.16μL/cm²,respectively.The fumigation activity of methyl salicylate with different dose on S.zeamais was determined by triangular flask fumigation.The results showed that the corrected mortality rate of S.zeamais enhanced significantly with the increase of treatment concentrations,and the its corrected mortality rate was 100%at 7.12μL/L for 48 h.The LC₅₀of methyl salicylate treated for 12,24,36 and 48 h were 7.14,5.75,4.55 and 4.29μL/L,respectively.4.Insecticidal mechanism of methyl salicylate against S.zeamais in vivoThe activities of acetylcholinesterase（ACh E）,glutathione-S-transferase（GST）,carboxylesterase（Car E）,catalase（CAT）,peroxidase（POD）and superoxide compound dismutase（SOD）were determined by triangular flask fumgation with different concentrations and time.The results showed that:（1）lowwer concentration of methyl salicylate induced the increase of ACh E activity,but ACh E activity was inhibited at higher concentration methyl salicylate,the same trend appears with the time effect;（2）methyl salicylate had inhibitory effects on GST and Car E activities at both time and dsoe level;（3）methyl salicylate had the same activaction trend on SOD activity,and the effect was more significant with the increase of treatment concentration and the extension of processing time;（4）methyl salicylate had different inhibitory effects on POD and CAT activities in vivo.5.Effect of methyl salicylate against S.zeamais in simulated warehouse environmentsThe insecticidal effect of methyl salicylate was tested in a simulated warehouse was tested at different time.The results showed that:under the condition of 28℃and total darkness,methyl salicylate（391.6μL/L）was used to fumigate the upper and middle S.zeamais for 20 d.The corrected mortality rates were 93.82%and 62.36%,and the LC₅₀were 223.26μL/L and 291.58μL/L,respectively.However,the control on the lower S.zeamais was not good.The corrected mortality rate was 47.75%.After the airtight fumigation with methyl salicylate（391.6μL/L）for 1,7,14 and 20 d at 28℃in total darkness,the control effciency increased with the extension of the treatment time,and the closer to the surface of the grain pile,the better the control effciency.