Yafei WANG，Runjie WEl，Hang ZHU，Xiaomao ZHOU，2*.Institute of Pesticide Science，Hunan Agricultural University，Changsha 4028，China；2.Hunan Academy of Agricultural Sciences，Changsha 4025，China

Determination of Resistance to Seven lnsecticides in Plutella xylostella L.in Fields of Northern Hunan

Yafei WANG1，Runjie WEl1，Hang ZHU1，Xiaomao ZHOU1，2*
1.Institute of Pesticide Science，Hunan Agricultural University，Changsha 410128，China；
2.Hunan Academy of Agricultural Sciences，Changsha 410125，China

The resistance of field populations of Plutella xylostella，from the three vegetable producing areas （Nianyuxu Town of Yueyang City，Canggang Town of Changde City and Shatou Town of Yiyang City）in northern Hunan，to seven insecticides was determined using leaf dipping method in door.The results showed that Plutella xylostella showed an extremely high-level resistance to beta-cypermethrin（resistance ratio，RR=257.13），a high-level resistance to abamectin（RR=135.15）and indoxacarb（RR=103.08）and a moderate-level resistance to chlorfenapyr and emamectin benzoate.But Plutella xylostella is relatively sensitive to chlorantraniliprole and Bacillus thuringiensis（Bt）.Therefore，the prevention of Plutella xylostella in northern Hunan should focus on the alternative use of chlorfenapyr，emamectin benzoate，chlorantraniliprole and Bacillus thuringiensis and avoid the use of beta-cypermethrin so as to delay the generation and development of resistance to insecticides in Plutella xylostella.

Plutella xylostella；Insecticide；Drug resistance determination

D iamondback moth （Plutella xylostella L.）is a major kind of injurious insect that harm the cruciferous plants worldwide［1］.The disaster of P.xylostella hap pened earliestin the Mediterranean［2］，but has been spread widely across the world［3］. P.xylostella can be found in all of the provinces of China.At present，the prevention and control of P.xylostella mainly focus on chemical control［4］. Due to frequent use of insecticides and overlapping of generations of P.xylostella，as well as its rapid propagation［5］，P.xylostella had developed resistance to insecticides in varying degrees［6］，resulting in great difficulty in preventing P.xylostella.Northern Hunan is an area with wide plantation of cruciferous vegetables and also the region with serious plague of P.xylostella［7］.Due to different use ranges and methods of insecticides，the resistance of P.xylostella to insecticides differs among different regions.In this study，the field populations of P.xylostella were collected from three vegetable producing areas of northern Hunan.Then their resistance to seven common insecticides，including betacypermethrin，abamectin，indoxacarb，chlorfenapyr，emamectin benzoate，chlorantraniliprole and B acillus thuringiensis （Bt），was determined so as to explore the current status of resistance in P.xylostella and provide theoretical references for scientific use of insecticides.

Material and Methods

lnsects

The field populations of P.xylostella were collected from the Nianyuxu Town of Yueyang City，Cangtang Town of Changde City and Shatou Town of Yiyang City in October，2014.Then the whole generation of P.xylostella was inoculated underexperimental conditions.The susceptible strains of P.xylostella were provided by the Henan Jiyuan Baiyun Industry Co.，Ltd.The susceptible strains had been preserved in the laboratory for ten years without exposure to insecticides.

Insecticides

The seven insecticides used in this study included 97.2%abamectin（Hebei Veyong Bio-Chemical Co.，Ltd.），97%indoxacarb（E.I.duPont de Nemours&Co.，Inc.），95.3%chlorantraniliprole（Du Pont China Holding Co.，Ltd），94.5%chlorfenapyr（BASF（China）Co.，Ltd.），95%beta-cypermethrin （Jiangsu Yangnong Chemical Group Co.，Ltd.），90%emamectin benzoate （Hebei Veyong Bio-Chemical Co.，Ltd.）and 16 000 IU/mg Bacillus thuringiensis （Yangzhou Luyuan Bio-Chemical Co.，Ltd.）.

Bioassay

The bioassays adopt the leaf dipping method［8］.According to previous tests，the concentrations at which the corrected death rate ranged from 10%to 90%were selected as the treatment concentrations.The water soluble insecticides were directly dissolved in water，while the others were mixed with appropriate acetone and then diluted into five concentration gradients with 0.1%Tween-80.The sterile distilled water and 0.1%Tween-80 were used as controls for both. Certain amount of fresh wild cabbage was sampled，cleaned and then cut into circular slices with diameter of 6.5 cm.The samples were immersed into insecticides for over 10 s，and then taken out and air dried naturally.Subsequently，the samples were placed into petri dishes laid with wet filter paper.Afterwards，new third-instar larvae of P.xylostella were put into the petri dishes （10 larvae per replication）. Each treatment had four replications. The bioassays were kept at a temperature of（25±1）℃.The photoperiod was L∶D=16 h∶8 h，and the relative humidity was 60%-70%.The death rates of the larvae were observed 48 h after the beginning of the experiment. If the larvae had no autonomous response when they were touched with writing brush，they were proved dead. If the death rate of the blank control is over 10%，the experiment is needs to be carried out again.The data collected from the experiment was statistically analyzed with Probit software so as to obtain the regression equations of virulences and to calculate the median lethal concentrations （LC50）at 95% confidence intervals，correlation coefficients，etc.

Results and Analysis

Sensitivity baselines of Plutella xylostella to different insecticides

The sensitivity baselines of P.xylostella to different insecticides were obtained by using leaf immersion method （Table 1）.As shown in Table 1，the LC50of abamectin was lowest（0.033 mg/L），followed by those of emamectin benzoate，indoxacarb，Bt and chlorfenapyr，while the LC50of beta-cypermethrin was highest（3.282 mg/L）.

Resistance levels of P.xylostella to seven insecticides in northern Hunan

As shown in Table 3，the field populations of P.xylostella had a moderate-level resistance to chlorfe napyr（RR=21.77-25.65）and emamectin benzoate（RR=28.77-39.04），a high-level resistance to abamectin （RR=76.06-135.15）and indoxacarb （RR=64.74-103.08）and an extremely high-level resistance to beta-cypermethrin （RR= 109.00-257.13）.However，P.xylostella showed a relatively high-level sensitivity to chlorantraniliprole and Bacillus thuringiensis.

Table 1 Susceptible baselines of P.xylostella to seven insecticides

Table 3 showed that the resistances of field population of P.xylostella from Yueyang to six out the seven insecticides，such as abame-ctin，chlorantraniliprole，chlorfenapyr，betacypermethrin，emamectin benzoate and Bt were higher than those from Changde and Yiyang，and the P.xylostella from Changde showed higher resistances to indoxacarb compared to those from Yueyang and Yiyang. Therefore，the P.xylostella from Yueyang had the highest resistances to insecticides，and more attention waspaid to its resistance management.

Table 3 Toxicities of seven insecticides to three field populations of P.xylostella in northern Hunan

Conclusions and Discussion

Since the use history and level of insecticides differ among different geographic areas，P.xylostella developed different-level sensitivity and resistance to insecticides［9］.In this study，field populations of P.xylostella were collected from the plain areas surrounding the Dongting Lake.Owing to favorable economic benefits，the plantation of brassicaceous vegetables account for a large proportion in planting industry，which is conducive to the propagation of field populations of P.xylostella.Farmers mainly adopt chemical control measures to control P.xylostella，resulting in large-dosage and large-area use of insecticides. However，P.xylostella will generate resistance to those chemical insecticides in a very short time，so most insecticides have already lost their control efficiencies.Therefore，it is very important to extent the useful life of insecticides by using these insecticides scientifically［10］.

In previous determination of resistance to insecticides in P.xylostella in central China，it has been found that P.xylostella has a very high-level resistance to beta-cypermethrin in various regions of central China［11］.The result of this study also showed that the resistance of P.xylostella to betacypermethrin was in a very high level. The control efficiency of abamectin may decline due to early and frequent use［12］.Compared with Changsha，which also belongs to northern Hunan，P.xylostella showed an extremely high resistance to indoxacarb in central China.The resistance of P.xylostella to insecticides has been improved from the moderate level in 2008 to high level at current［13］.Although the collected field populations of P.xylostella are sensitive to Bt，they are screened in the lab and there are still over 20 kinds of injurious insects showing level-varying resistances to Bt［1 4］，indicating that the field populations of injurious insects may have potential resistance to insecticides under certain conditions［15］.

Therefore， the prevention of Plutella xylostella in northern Hunan should focus on the alternative use of chlorfenapyr，emamectin benzoate， chlorantraniliprole and Bacillus thuringiensis and avoid the use of beta-cypermethrin so as to delay the generation and development of resistance to insecticides in Plutella xylostella.

References

［1］SARFRAZ RM，DOSDALL LM，KEDDIE AB，et al.Larval survival，host plant preferences and developmental responses of the diamondback moth，Plutella xylostella（Lepidoptera:Plutellidae）on wild brassicaceous species［J］. Entomological Science，2011，14（1）: 20-30.

［2］HARCOURT D G.The biology and ecology of the diamondback moth，Plutella maculipennis Curtis，in eastern Ontario［M］.Cornell Univ.，1954.

［3］ZALUCKI MP，F(xiàn)URLONG MJ.Predicting outbreaks of a migratory pest:an analysis of DBM distribution and abundance revisited ［C］//SRINIVASAN R，SHELTON AM，COLLINS HL.Management of the diamondback moth and other crucifer insect pests:Proceedings of the Sixth International Workshop. Shanhua，Taiwan:AVRDC–The World Vegetable Center，2011.

［4］SRINIVASAN R，SHELTON AM，COLLINS HL，et al.Proceedings of the sixth international workshop on management

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湘北地區(qū)田間小菜蛾對七種殺蟲劑的抗藥性測定

王雅菲1，魏潤潔1，朱航1，周小毛1，2*（1.湖南農業(yè)大學農藥研究所，湖南長沙 410128；2.湖南省農業(yè)科學院，湖南長沙 410125）

在室內采用浸葉法測定湘北三個蔬菜產區(qū)（岳陽鲇魚須鎮(zhèn)，常德滄港鎮(zhèn)，益陽沙頭鎮(zhèn)）的田間小菜蛾對7種藥劑的抗藥性。實驗結果表明，小菜蛾對高效氯氰菊酯抗性達到極高水平（抗性倍數為257.13）；對阿維菌素，和茚蟲威抗性屬于高抗水平（抗性倍數為135.15和103.08）；對溴蟲腈、甲氨基阿維菌素苯甲酸鹽屬于中抗水平；對氯蟲苯甲酰胺和蘇云金桿菌相對敏感。因此，湘北地區(qū)的小菜蛾防治應該注重溴蟲腈、甲氨基阿維菌素苯甲酸鹽、氯蟲苯甲酰胺和蘇云金桿菌交替使用，停止高效氯的使用，以便延緩抗藥性的產生與發(fā)展。

小菜蛾；殺蟲藥劑；抗藥性監(jiān)測

ABCC2基因在小菜蛾茚蟲威抗性中的功能分析（31371966）。

王雅菲（1989-），女，湖南岳陽人，在讀碩士研究生，E-mail：zoeff@qq.com。*通訊作者，博士，教授，E-mail：zhouxm1972@126. com。

2015-01-06

2015-00-00

Supported by Functional Analysis of ABCC2 Proten Gene in Indoxacarb Tesistant Diamondback Month，Plutella xylostella（31371996）.

.E-mail:zhouxm1972@126.com

January 6，2015Accepted:000