Screening Of Stomach Toxicity Insecticides And The Effects Of Detoxifying Enzymes Activity In Bactrocera Dorsalis Under Sublethal Doses Of Three Insecticides

Bactrocera dorsalis（Hendel）has a wide range of hosts,with strong reproductive and dispersal ability,which can cause damage to more than 350 kinds of fruits and vegetables.In China,the occurrence and damage of B.dorsalis has caused extremely serious economic losses to the fruit and vegetable industry,and it has shown an increasing trend in recent years.It has become one of the main methods to control B.dorsalis by using highly effective stomach toxicity insecticides processing as bait.In this study,a kind of liquid feeding method with simple operation and good repeatability was used to screen out some highly effective stomach toxicity insecticides to B.dorsalis adults.By using the methods of mutual determination and the method of co-toxicity coefficient（CTC）,the highly effective insecticides formulas were further screened out.The activities of Glutathione S-transferase（GST）,Carboxylesterase（CarE）and Insect cytochrome P450（CYP450）in adult B.dorsalis treated with sublethal dose of selected insecticides were investigated.The results provide reference for the selection and rational mixture of stomach toxicity insecticides and delay insecticides resistance of B.dorsalis adults.The main results as follows:1.The acute toxicity of 23 insecticides to B.dorsalis adults was determined by liquid feeding method.It was found that fenvalerate,spinosad,clothianidin,avermectin,ivermectin,thiamethoxam,dinotefuran,phoxim and chlorpyrifos had high toxicity to the adults of B.dorsalis.The LC₅₀-24hours values were 2.791 mg/L,3.204 mg/L,3.257 mg/L,4.312 mg/L,4.480 mg/L,4.696 mg/L,5.859 mg/L,6.614 mg/L and 6.667 mg/L,respectively,while LC₅₀-48hours values were 1.560 mg/L,0.936 mg/L,1.002 mg/L,2.025 mg/L,2.115 mg/L,2.765 mg/L,2.857 mg/L,5.271 mg/L and 5.630 mg/L.The toxicity of fenvalerate was the highest in 24 hours,while spinosad was the highest in 48 hours.2.The combined toxicity of spinosad,clothianidin,fenvalerate and avermectin to B.dorsalis adults was determined by the methods of mutual determination and CTC.Three compound formulations were selected,which were spinosad and clothianidin（active ingredient ratio 44:5）,spinosad and fenvalerate（active ingredient ratio 11:10）,spinosad and avermectin（active ingredient ratio 7:10）,respectively.Among them,spinosad and fenvalerate（active ingredient ratio 11:10）was the highest degree of toxicity values to B.dorsalis adults.3.The activities of GST,CarE and CYP450 of B.dorsalis adults were determined when they were treated with sublethal dose of spinosad(LC₃₅=2.079 mg/L),fenvalerate(LC₃₅=2.236 mg/L)and a mixture of spinosad and fenvalerate containing 11:10 active ingredient(LC₃₅=1.667 mg/L),respectively.With passage of time,it was found that spinosad,fenvalerate and the mixture of spinosad and fenvalerate showed different degrees of inhibitory effects on the activity of CarE and CYP450 in B.dorsalis adults,with the activity of GST increased.The results showed that three detoxifying enzymes were involved in the detoxication of B.dorsalis adults in different degree,among which the compound of spinosad and fenvalerate with the active component ratio of 11:10 had the most significant inhibitory effect on CYP450.It is speculated that the mixture can decrease the amount of CYP450 by reducing B.dorsalis adults’detoxification ability.To sum up,9 kinds of stomach toxicity insecticides for controlling B.dorsalis adults were selected by liquid feeding test method under lab conditions,three compound formulations were selected in the end.The changes of activity of detoxifying enzyme system in B.dorsalis adults were discussed.The results of this study provide a reference for the selection,proper mixture of stomach toxicity insecticides and the delay of insecticides resistance to control B.dorsalis adults,and provide the basis for the determining detoxification metabolism in B.dorsalis adults.