| The brown planthopper,Nilaparvata lugens(st(?)l) is one of the major migratory insects on rice in Asia.In recent years,N.lugens outbreaks have occurred more frequently in Yangtze River Delta areas and the Southern areas in China.Currently,chemical control is still a major method for suppressing N.lugens.Resistance development to conventional insecticides,such as organophosphate and carbamate insecticides,was documented in many Asian countries.Development of resistance of N.lugens to insecticides might be a major reason for continuous increase of occurring areas and frequent outbreaks in recent years.Laboratory screen of altemative insecticides for replacing highly-toxic organophos -phate insecticides,assessment of fertility effect of pyrethroidd against N.lugens,and monitoring of insecticide resistance in N.lugens were conducted in this study.An imidacloprid-resistant strain of N.lugens was selected developed in laboratory.In order to provide basis for insecticide resistance management in N.lugens and feasibility of adoption of pyrethroids in rice paddy,cross-resistance,biochemical mechanism of the resistance, resistance stability and resistance inheritance were further investigated.Some valuable breakthroughs had been achieved.The results were summarized as follows:1 Insecticide resistance detection and monitoring in N.lugensIn recent years,frequent outbreaks of N.lugens in many Asian countries became a serious threat for rice production.Chemical control is still the most effective way to control N.lugens.In order to carry on insecticides resistance management,it was necessary to find out the current susceptibility or resistance of N.lugens to insecticides.A total of 30 populations of N.lugens from nine provinces were examined from 2005 to 2007 for their resistance levels to several insecticides.Results showed that substantial variations of the resistance level to different insecticides existed in N.lugens.Field populations developed high to extremely high resistance to imidacloprid(RR=79.1- to 813.5-fold),low to medium resistance to buprofezin,fipronil and thiamethoxam with resistance ratios up to 13.1-,29.8- and 19.5-fold,respectively.Long term use of imidacloprid in wide rice growing areas might be associated with the high level of resistance in N.lugens.Therefore,resistance management strategies must be developed to prevent the resistance from further increase.2 Resistance risk assessment of imidacloprid resistance in N.lugensA laboratory population was selected continuously with imidacloprid in the laboratory. After 26 generations,the resistance ratio increased from 200.1- to 1671.3-fold(LC50 value from 16.0 mg a.i./ L to 133.7 mg a.i./ L) with the resitance ratio increased by 8.4-fold,and the estimate of realized heritability(h2) was 0.1049.The results showed that continuous selection with imidacloprid could further increase the resistance level even a high resistance level had already developed in the population.The 6th selected generation was allocated for selection interruption testing.After 17 generations without imidacloprid selection,the resistance ratio descended from 759- to 114.1- fold.Results suggested that a slow or incomplete recovery of the susceptibility was achievable even the population of N.lugens once developed high resistance level to imidacloprid.Therefore,it was very urgent that resistance management strategies of N.lugens to imidacloprid must be strengthened.3 Cross-resistance of imidacloprid resistance in N.lugensDevelopment of resistance to imidacloprid in N.lugens might be a major reason for continuous increase of occurring areas and frequent outbreak in recent years.Control of N. lugens heavily depended on chemical insecticides.To provide resistance assessment for the national insecticide resistance management program,a laboratory population was selected continuously with imidacloprid to determine the cross-resistance of imidacloprid to other insecticides in N.lugens.In this study,we detected obvious cross-resistance between imidaclothiz and thiacloprid,but not to dinotefuran,thiamethoxam,and nitenpyram,in a highly imidacloprid-resistant strain of N.lugens.In addition,the highly imidacloprid resistance strain of N.lugens also showed no cross-resistance to fipronil(a phenylpyazole insecticide) and buprofezin(an insect growth regulator).Therefore,to relieve imidacloprid selection pressure and to recover imidacloprid susceptibility in N.lugens,we suggested that thiamethoxam,nitenpyram,buprofezin,and fiprornil can be used for alternating and rotating to control N.lugens in the resistance management program.4 Genetics of imidacloprid resistance in N.lugensThe inheritance of insecticide resistance in insect pests is not only an important factor affecting the development of resistant,but also the basis for formulating resistance management strategy.The genetic basis of imidacloprid resistance in N.lugens was investigated in this study.Logit regression analysis of F1 reciprocal crosses between resistant and susceptible strain of N.lugens indicated that LC50 of the progenies from F1 and F1' were 25.68(21.64～30.57) mg a.i./L and 31.09(25.35～36.24) mg a.i./L, respectively,and there were no significant difference between the two LC50 values.This results showed the gene(or genes) that confers resistance to imidacloprid was on autosome. According to the formula of Stone(1968),the dominance degree(D) of F1 and F1' were 0.58 and 0.63,respectively.This indicated that resistance was inhetited as an incompeletely dominance trait(1＞D＞0).LD-P curves for progenies of the backcrosses and F2,F2' were apparently different from correspongding expected curves assuming monogenic inheritance. Theχ2 analysis confirmed that observed mortalities failed to fit the monogenetic model, which supports the conclusion that resistance to tebufenozide conferred by more than one factor.5 Mechanisms for imidacloprid resistance in N.lugensSynergism experiment in vitro with TPP,PBO and DEM was performed to survey the roles of detoxication enzymes in imidacloprid resistance strain of N.lugens.The results indicated that PBO had significant synergistic effect on imidacloprid toxicity in both resistant(SR 2.3) and susceptible strain(SR 1.5).TPP also synergized imidacloprid toxicity (SR 1.5) in the resistant strain but not in the susceptible borer(SR 1.0).However,DEM showed no obvious synergism in both resistant and susceptible strain.Enzyme activity assay demonstrated that the resistant strain had higher activity of microsomal O-demethylase and esterase than the susceptible strain(1.6- and 1.5-fold,respectively). PBO and TPP can effectively eliminate the resistance ratio in the resistant population for 57 and 35 percent,respectively.PBO combined with TPP can inhibit the resistance ratio in the resistant population up to 92 percent.Therefore,the major resistance mechanism to imidacloprid in N.lugens was metabolic resistance.6 Laboratory screen of alternative insecticides for replacing highly-toxic insecticides for controlling N.lugensFive highly-toxic organophosphate insecticides were once widely used for a long time to control important pests on rice and other food crops in China.Before the five highly-toxic organophosphate insecticides were completely banned in the Jannary 1,2007, it was very urgent to screen altemative insecticides for replacing the highly-toxic insecticides for controlling N.lugens.We examined more than 20 insecticides(categorized as six classes) in 2005 for their laboratory toxicity against N.lugens collected from different rice ecological zones(Nanning and Guilin in Guangxi,Changde in Hunan, Nanjing in Jiangsu).Results showed that buprofezin,fipronil,thiamethoxam,nitenpyram, chlopyrifos,isoprocarb,promecarb,and carbosulfan had potential to be adopted as alternative insecticides to replace the highly-toxic pesticides.Providing field trials,safety assessment to nature enemy,and resistance risk assessment to be conducted,this study provided basis for selecting alternative insecticides for replacing the highly-toxic for controlling N.lugens.7 Assessment of biological activity and fertility effect of pyrethroids against N.lugensTo provide basis for applying pyrethroids in rice paddy,this study was conducted to determine the biological activity and fertility effect against N.lugens of pyrethroids. Results showed that silafluofen and ethofenprox had relative high toxicity against N.lugens and the toxicity levels were as:silafluofen＞ethofenprox＞beta-cypermethrin,triazophos, methamidophos,beta-cyfluthrin≥esfenvalerate,lambda-cyhalothrin＞deltamethrin, alpha-cypermethrin＞fenpropathrin＞cycloprothrin.After N.lugens was treated separately with the sub-lethal dose(LC5) of beta-cypermethrin and lambda-cyhalothrin,for 10 generations,the egg-productions of N.lugens were obviously higher than that of control, but there was no significant difference between the two pyrethroids and triazophos (P＜0.05).Moreover,the mixture of pyrethroids and buprofezin can effectively suppress the egg-production of N.lugens.Potential use of pyrethroids in rice paddy was also discussed in this article.
|
PDF Full Text Request