Resistance Dynamics Of Bactrocera Dorsalis(Hendel) Resistant Strains To Three Insecticides

Bactrocera dorsalis（Hendel）was one of the important pests in the fruits and vegetables production in South China in past thirty years.In controlling this pest in the fields,chemicals with the low costing,operation easily and rapid response,have been the most common measure over the years.Therefore,the resistance of B.dorsalis to different kinds of insecticides has appeared and developed under with the unscientific usages of chemicals.For understanding the resistance dynamic of this fruit fly,the cross-resistance and resistance inheritance of the oriental fruit fly to Beta-cypermethrin,Trichlorfon and Abamectin were studied in this paper,then the resistance dynamics of three resistant strains under different selection frequency were explained.The conclusion revealed the scientific interval for resistance management in using those insecticides to control the fruit fly.The main results were as follows.1.Cross Resistance of B.dorsalis to Beta-cypermethrin,Trichlorfon and Abamectin.It was indicated that cross resistance among beta-cypermethrin,trichlorfon and abamectin for B.dorsalis has been existent in this experiment.B.dorsalis adults with high resistance to beta-cypermethrin（BcR-H）displayed the medium cross-resistance to trichlorfon and low cross-resistance to abamectin.The B.dorsalis strain with medium resistance to trichlorfon（TrR-M）both showed the low cross-resistance to beta-cypermethrin and abamectin,while another strain with medium resistance to abamectin（AbR-M）also was low cross-resistance to beta-cypermethrin and trichlorfon.2.Resistance Inheritance of Beta-cypermethrin,Trichlorfon and Abamectin in B.dorsalis.The inheritance of B.dorsalis resistance to beta-cypermethrin,trichlorfon and abamectin was tested and analyzed.The conclusion indicated,compared with parents,the resistance of F₁ strains had declined to some extents,when male and female adults of threeWhen the beta-cypermethrin-resistant strain mated with the trichlorfon-resistant one,comparing to the parents,the levels of resistance to beta-cypermethrin decreased significantly in both F₁ strains of quadrature and reciprocal cross,the declined rate of quadrature F₁ resistance was 33.5%while the reciprocal cross F₁ was 56.4%.When mated to the abamectin-resistant strain,the quadrature F₁ resistance to beta-cypermethrin changed hardly with the declined rate 8.5%,but the reciprocal cross F₁ resistance decreased significantly with 84.2%declined.The quadrature F₁ resistances were both significant higher than the reciprocal cross F₁,which was indicated that the resistance of B.dorsalis to beta-cypermethrin was more inclined to maternal inheritance.When the trichlorfon-resistant strain mated with the beta-cypermethrin-resistant strain,comparing to parents,the both F₁ strains resistances to trichlorfon decreased significantly.The declined rate of F₁ strains resistances after quadrature and reciprocal cross were 21.4%and 81.5%.Comparing to parents,both quadrature F₁ and reciprocal cross F₁ resistances also decreased significantly when they mated to the abamectin-resistant strain,and the declined rate of quadrature F₁ and reciprocal cross F₁ resistances were 38.0%and 79.0%.The resistance of quadrature F₁ was higher than the reciprocal cross F₁,which showed that the resistance of B.dorsalis to trichlorfon mainly belonged to maternal inheritance.When abamectin-resistant strain mated to the beta-cypermethrin-resistant strain,the quadrature F₁ resistance to abamectin changed hardly with the declined rate only 3.6%,while it was up to 65.5%for the F₁ strain after reciprocal cross.When mating to the trichlorfon-resistant strain,the declined rates of quadrature F1 and reciprocal cross F₁resistances were 12.8%and 62.3%.The quadrature F₁ resistance was also higher than the reciprocal cross F₁,which indicated that the resistance of B.dorsalis to abamectin conformed to the maternal inheritance.3.Resistance Dynamics of B.dorsalis Resistant Strains to Beta-cypermethrin,Trichlorfon and Abamectin while Selected with Different Frequency.Study on the resistance development of B.dorsaliswith resistant strains by using beta-cypermethrin,trichlorfon and abamectin with different frequency.The results indicated that 270 days later,when resistance-selection was taken once rised to 1133.6 mg/L from the first time 582.7 mg/L,and the resistant multiple increased to190.7 folds from 98.0 folds.The median lethal concentration to trichlorfon was up to70.6mg/L from the first time 45.3mg/L,and the resistant multiple rised to 20.2 folds from13.0 folds.The median lethal concentration to abamectin went up to 158.4mg/L from the first time 102.6mg/L,and the resistant multiple varied from 47.4 folds to 73.1 folds.When resistance-selection was taken once every 60 days,the median lethal concentrations to beta-cypermethrin,trichlorfon and abamectin were up to 828.0 mg/L,56.8mg/L and136.6mg/L,respectively,and the resistant multiples were up to 139.3 folds,16.3 folds and63.1 folds.When resistance-selection was taken once every 90 days,the median lethal concentrations to beta-cypermethrin,trichlorfon and abamectin were 529.2 mg/L,38.9mg/L and 80.2mg/L,respectively,and the resistant multiples were 89.0 folds,11.1 folds and 37.0folds.When resistance-selection was taken once every 120 days,the median lethal concentration and resistant multiple to beta-cypermethrin were 511.3 mg/L and 86.0 folds,and the median lethal concentration and resistant multiple to trichlorfon were 36.3 mg/L and 10.4 folds while 79.0 mg/L and 36.5 folds to abamectin.These resistant strains without contact any pesticide were as control group,270 days later,the median lethal concentration to beta-cypermethrin decreased to 368.1 mg/L from 582.7 mg/L,and the resistant multiple decreased to 61.9 folds from 98.0 folds.The median lethal concentration to trichlorfon decreased to 30.5 mg/L from 45.3 mg/L,and the resistant multiple decreased to 8.7 folds from 13.0 folds.The median lethal concentration to abamectin decreased to 68.3 mg/L from102.6 mg/L,and the resistant multiple decreased to 31.5 folds from 47.4 folds.Equations were presented to fit the relationship between the time interval of resistance-selection and the growth rate of resistance after 270 days,respectively,the equations were Y=11.427X^-0.529（beta-cypermethrin）,Y=6.0207X^-0.405（trichlorfon）and Y=6.3444X^-0.421（abamectin）.They all indicated that the resistance development of B.dorsalis adults under different resistance-selection types by beta-cypermethrin,trichlorfon and abamectin were conformed to the power model.These simulated results showed,when these three insecticides were used to control B.dorsalis adult,their resistance risk for going up continuously after 270 days can reduce under the condition of over 99 days as time interval for abamectin between the successive usage.