Study On The Insecticidal Activity And Mechanism Of 7-hydroxycoumarin Against The Larvae Of Lymantria Dispar

In order to explore the insecticidal activity and mechanism of 7-hydroxycoumarin on Lymantria dispar larvae,the toxicity equation of 7-hydroxycoumarin on Lymantria dispar larvae was determined in this experiment.The effects of 7-hydroxycoumarin on growth and nutrient utilization of gypsy moth were investigated by measuring food intake,relative growth and fecal volume.The effects of 7-hydroxy-coumarin on the redox systems of Lymantria dispar larvae were investigated by measuring the contents of H₂O₂,MDA and T-AOC.The effects of 7-hydroxycoumarin on antioxidant enzyme activity and m RNA transcription levels of Lymantria dispar larvae were investigated by measuring the content of 7-hydroxycoumarin.The expression level of 7-hydroxycoumarin on Lymantria dispar apoptosis gene was determined to explore the mechanism of 7-hydroxycoumarin on Lymantria dispar larvae apoptosis,so as to provide theoretical basis for further development and utilization of 7-hydroxycoumarin and prevention and control of Lymantria dispar larvae.（1）7-hydroxycoumarin have good toxic activity against the larvae of Lymantria dispar,The sublethal concentration(LC₂₀)of 7-hydroxycoumarin was 0.166 mg/g and the medium lethal concentration(LC₅₀)was 0.307 mg/g at 72 h.Both the sublethal and medium lethal concentrations of 7-hydroxycoumarin were able to significantly inhibit the feeding,body weight gain,fecal volume and relative growth rate of Lymantria dispar larvae.After 72 h of feeding on the diet containing 7-hydroxycoumarin,the food utilization and conversion rate of the LC₂₀-treated larvae were significantly reduced to 42.15%and 75.73%of the control group,respectively;the food utilization and conversion rate of the LC₅₀-treated group were significantly reduced to 30.09%and 78.80%of the control group,respectively,and the food utilization and conversion rate of the LC₂₀-treated and LC₅₀-treated groups were similarly reduced to those of the control group.The digestibility rate increased significantly to 1.34 and1.31 times of the control group,respectively,compared to the control group,and Lymantria dispar larvae were able to reduce the negative effects of 7-hydroxycoumarin on their food utilization by increasing their digestibility of food.（2）7-hydroxycoumarin induced oxidative stress in Lymantria dispar larvae.7-hydroxycoumarin significantly increased the contents of both H₂O₂and MDA in Lymantria dispar larvae（P<0.05）and significantly decreased the total antioxidant power（T-AOC）in Lymantria dispar larvae（P<0.05）,indicating that 7-hydroxycoumarin could bring damage to the redox system of Lymantria dispar larvae.After 24,48 and 72 h of coumarin treatment,the H₂O₂content in Lymantria dispar larva was significantly increased to 1.54,2.21 and 1.81 times that of the control;the H₂O₂content was significantly increased（P<0.05）to 1.53,1.71 and2.58 times that of the control;the T-AOC was significantly decreased（P<0.05）to 86.69%,78.05%and 80.99%,respectively.（3）7-hydroxycoumarin can activate antioxidant enzyme activity.The activities of SOD,CAT and POD in Lymantria dispar larvae were significantly activated by 7-hydroxycoumarin.The contents of SOD,CAT and POD in Lymantria dispar larvae after 72 h were increased by1.30,1.26 and 1.68 times compared with those in control group,respectively.SOD gene expression was also significantly up-regulated at 72 h,and SOD1 and SOD2 were up regulated by 2.94 and 1.95 times compared with the control group,respectively.The expression level of CAT enzyme at m RNA level was also significantly up-regulated at 72 h,which was 2.86 times higher than that of the control group,and the trend was consistent with the enzyme activity level.These results indicate that 7-hydroxycoumarin can activate antioxidant enzyme activity and m RNA expression.（4）7-hydroxycoumarin induces apoptosis through ROS mediated JAK-STAT and mitochondrial pathways.After 7-hydroxycoumarin treatment,the expressions of JAK and STAT were significantly decreased（P<0.05）,indicating that 7-hydroxycoumarin inhibited JAK-STAT signaling pathway.In addition,the expressions of Cyt-c,caspase9 and caspase3 were significantly increased（P<0.05）,indicating that 7-hydroxycoumarin could activate the mitochondrial apoptosis pathway.These results indicate that 7-hydroxycoumarin can inhibit the JAK-STAT signaling pathway,activate the mitochondrial apoptosis pathway,and induce midgut cell apoptosis,resulting in the midgut injury of Lymantria dispar.