Resistance Monitoring And Sublethal Effect Of Acaricides On Panonychus Ulmi Koch From Shaanxi Province

The European red mite（Panonychus ulmi Koch）is an important pest in apple orchards and is widely distributed in China.This pest damages apple buds and leaves with nymphs and adults.The damaged buds cannot germinate normally,resulting in decreasing of apple quality and yield.The control of P.ulmi mainly depends on spraying chemical.The long-term unreasonable use of acaricides has led to the acaricide resistance of P.ulmi field populations.It is of great significance to clarify the resistance level of P.ulmi to acaricides and the sublethal effect of chemicals.In this study,the population dynamics of P.ulmi in apple orchards in Yangling,Shaanxi Province were investigated.The resistance of nine P.ulmi field populations in Shaanxi to five commonly used acaricides was monitored.The effects of sublethal concentrations of pyridaben and bifenazate on the growth,development and reproduction of P.ulmi were studied.The changes of related detoxification enzyme activities after treatment with sublethal concentrations of two insecticides were analyzed.The main results are as follows:1.Population dynamics and spatial distribution pattern of P.ulmiThe population dynamics of P.ulmi in apple orchards in Yangling area were investigated.The results showed that there were two peaks for the population of P.ulmi in Yangling in one year.The first peak of population was in early July and the second was in mid-August.The spatial distribution pattern of the P.ulmi population was analyzed and determined.The results showed that the spatial aggregation index of P.ulmi was m*>0,I>0,C>1,m*/m>1,Ca>0,0<k<8,indicating that the mite was aggregated in the apple orchard.There was mutual attraction between individuals and the individual groups are the main distribution form.The mite aggregation was resulted from the population aggregation habits and the apple orchard environments.2.Susceptibility of P.ulmi to acaricidesThe toxicity of five acaricides to laboratory relative susceptible populations of P.ulmi was determined by slide-dip method.The results showed that the toxicity of abamectin was the highest(LC₅₀=0.009 mg/L),and the toxicity of bifenazate was the lowest(LC₅₀=157.627 mg/L).The toxicity of the five acaricides to the susceptible strain of P.ulmi was abamectin>pyridaben>azocyclotin>spirodiclofen>bifenazate.3.Acaricide resistance monitoring of P.ulmi field population in Shaanxi ProvinceThe resistance of P.ulmi field populations to acaricides in apple orchards in Shaanxi Province was monitored for two consecutive years.It was found that the mite had developed low to moderate resistance to pyridaben,azocyclotin and spirodiclofen,whilest was still in the stage of decreased sensitivity and low level resistance to abamectin.Most P.ulmi populations had not developed resistance to bifenazate.Fufeng（FF）,Liquan（LQ）,Fengxiang（FF）,Xingping（XP）,Baishui（BS）,Qianxian（QX）,Xunyi（XY）,Huangling（HL）and Luochuan（LC）showed more serious resistance to the five acaricide,followed by Xingping（XP）and Baishui（BS）populations.The resistance of P.ulmi populations in Qianxian（QX）,Xunyi（XY）,Huangling（HL）and Luochuan（LC）was relatively low.The resistance levels of P.ulmi varied among different regions.4.Sublethal effects of pyridaben and bifenazate on P.ulmiThe toxicity of pyridaben and bifenazate to female adults and eggs of P.ulmi was determined.The female adults treated with sublethal concentrations of pyridaben and bifenazate could significantly reduce the egg production,egg hatching rate and adult longevity of P.ulmi.The sublethal concentrations of pyridaben and bifenazate reduced the survival rate（l_x）and specific time fecundity（m_x）of P.ulmi.The sublethal concentrations of pyridaben and bifenazate had inhibition on the growth and population reproduction of the F₁generation of P.ulmi.When the female adults were treated with sublethal concentrations of pyridaben,the larval and nymphal stages were prolonged compared with the control,and the adult stage was significantly shortened.When the eggs were treated with sublethal concentrations of pyridaben treatment,the larval stage and nymph stage were significantly prolonged compared with the control,and the adult stage and longevity were shortened.The egg stage was significantly shortened after LC₁₀pyridaben treatment,while the F₁egg stage was significantly prolonged after LC₃₀pyridaben treatment.When the female adults were treated with sublethal concentrations of bifenazate,the egg stage was significantly prolonged and the adult stage was significantly shortened.When the eggs were treated with sublethal concentrations of bifenazate,the egg stage,larval stage and nymph stage of F₁generation were significantly prolonged,and the adult stage and longevity were significantly shortened.The population doubling time（Dt）was prolonged,whereas the net reproductive rate（R₀）,intrinsic rate of increase（r_m）and finite rate of increase（λ）were decreased after sublethal concentrations of pyridaben and bifenazate treatments.5.Effects of sublethal concentrations of pyridaben and bifenazate on detoxification enzymes of P.ulmiSublethal doses of pyridaben and bifenazate had significant induction effects on GSTs,P450s and Car Es in P.ulmi.The specific activities of GSTs,P450s and Car Es increased by 4.91-5.57 times,2.11-1.79 times and 1.41-1.76 times,respectively,after treatment with pyridaben at LC₁₀and LC₃₀,which were significantly higher than those of the control.The specific activities of P450s and Car Es in LC₁₀and LC₃₀after bifenazate treatment were significantly higher than those in the control,which increased by 1.64-2.07 times and 1.47-1.57 times,respectively.The GSTs specific activity in the LC₃₀treatment group was significantly higher than that in the control.