The Sublethal Effects Of Emamectin Benzoate On Bactrocera Dorsalis(Hendel)

The oriental fruit fly,Bactrocera dorsalis（Hendel）is a global pest.It can damage a variety of fruit varieties and seriously cause the loss of the yield and quality of agricultural productions.Chemical control is one of the main measures to prevent and control it,however,the extensive use of insecticides can easily cause the"3R"problem.Clarifying the sublethal effect of insecticides on Bactrocera dorsalis is great significance for the rational use of insecticides and environmental protection.Emamectin benzoate,with broad spectrum,high efficiency,low toxicity,has high application potential in the comprehensive management on Bactrocera dorsalis.However,the effect of the sublethal dose of emamectin benzoate on Bactrocera dorsalis has not been reported yet.In this study,the toxicity of contact and oral to Bactrocera dorsalis was measured,and the effects of the treatment with sublethal dose of emamectin benzoate on its reproduction,growth and detoxification enzyme activities were investigated,the sublethal effect of emamectin benzoate on Bactrocera dorsalis was preliminarily determined.The results are as follows:1.In order to determine the sensitivity of Bactrocera dorsalis adults to emamectin benzoate,the oral toxicity and contact toxicity were measured with feeding and film method respectively.The results showed that emamectin benzoate had strong acute lethal activity on Bactrocera dorsalis under the two toxicity,for the median lethal concentrations of oral toxicity at 24 h,48 h and 72h were 0.178 mg/L,0.125 mg/L and 0.085 mg/L,respectively;The median lethal concentrations of contact toxicity at 24 h,48 h and 72 h were 1.702 mg/L、0.234 mg/L、0.059 mg/L,respectively.The sensitivity of the field population in Guangxi to emamectin benzoate was determined,and it was found that the median lethal concentrations of contact toxicity was only 2.5～4.5 times that of the sensitive strain,indicating that it was still at the sensitive stage.2.The change dynamic of the sublethal dose of emamectin benzoate on Bactrocera dorsalis mating behavior,the age of the first spawning and the number of egg were determined under different treatments of oral and contract toxicity.Under the toxicity of oral,both males and females of Bactrocera dorsalis were exposed to emamectin benzoate of LC₁₀ dose,the total mating times of adults were significantly increased,when both sexes were exposed to LC₂₅ dose,the age of first spawning was delayed,but the mating and the number of oviposition was not significantly changed.There were no significant changes in the mating behavior and fecundity of orange musca dorsalis when the female or male were exposed to the sublethal dose of emamectin benzoate alone.Under the toxicity of contact,the mating and oviposition progenies were prolonged and the mating times decreased when both sexes were exposed to the LC₂₅ dose of emamectin benzoate.It was not conducive to the mating of male and female,but the spawning amount increased significantly when males exposed to LC₂₅ dose,as well as LC₁₀ dose.Females exposed to the LC₂₅ dose of emamectin benzoate,the first spawning day was delayed and had no significant effect on fecundity.The results showed that the effect of oral toxicity could promote the mating frequency of oriental fruit fly,but could not affect the oviposition.Contract toxicity could inhibit the mating frequency of oriental fruit fly,but can promote the number of eggs.3.The life span of male and female was shortened after the treatment of adult with the sublethal dose of emamectin benzoate,which had a greater influence on the life span of male.The life span of male worms was shortened more obviously in the contact treatment with LC₂₅ than that with the oral toxicity treatment with emamectin benzoate.There were no significant changes in eggs hatching rate,pupa duration,pupa weight,pupation rate and sex ratio of the offspring.The results showed that the sublethal dose of emamectin benzoate had adverse effects on the development of Bactrocera dorsalis adults,but had no significant effect on the reproduction of offspring.4.The activities or concentration of glutathione-s-transferase（GSTs）,carboxyesterase（Car E）,multifunctional oxidase（MFO）and acetylcholinesterase（ACh E）of Bactrocera dorsalis exposed at the doses of LC₁₀,LC₂₅ and LC₅₀ of emamectin benzoate feeding at 24 h,48 h and 72 h were determined.The results showed that duiring 24 h to 72 h the Car E activity was significantly inhibited;The activity of GST was promoted by low dose of emamectin benzoate and was firstly promoted,then inhibited and then stabilized by high dose;While the concentration of MFO increased first,then decreased and then increased again.MFO was firstly promoted,then suppressed and then promoted;At high dose of emamectin benzoate,ACh E was inhibited and then stabilized,while activity was increased significantly at the dose of LC₂₅.To sum up,emamectin benzoate has a high toxicity to Bactrocera dorsalis,the sublethal dose of its can inhibit the activity of carboxylesterase and shorten the life of adults,but it may stimulate the reproduction of oriental fruit fly population.The results provide a reference for the scientific and rational control of oriental fruit fly with emamectin benzoate.