Resistance Monitoring And Risk Assessment Of Emamectin Benzoate In Helico Verpa Armigera

The cotton bollworm,Helicoverpa armigera(Hubner),is a pest belonging to Lepidoptera,Noctuidae and a polyphagous insect pest with more than 250 different hosts.This pest is widespreadly distributed in the eastern hemisphere including Europe,Asia,Africa and Oceania.Before 2013,it is considered a quarantine pest in Amerian continent,but now occurres in Brazil and Puerto Rico.Since the 1950s,for the intensive use of the chemical pesticides on it,H.armigera has developed resistance to different classes of insecticides including organochlorine,organophosphorus,carbamate,pyrethroid,and some new insecticides.Along with the commercial planting of the transgenic Bt cotton in 1997,the cotton bollworm has been effectively controlled and the use of insecticides is reduced.But there are some new problems,such as the mired bugs become the major pests in the cotton field,the expression of Bt protein is decline in the late cotton season and the risk of resistance to Bt protein is pressing.Therefore,the chemical control is still an important strategy to the control of cotton bollworm.In this study,for the better understanding of insecticide resistance status in H.armigera,the resistance monitoring to emamectin benzoate,cyhalothrin and phoxim were conducted on the 14 field populations from different cotton area.By the selection of emamectin benzoate to the lab susceptible strain SCD,the resistance risk to this insecticide was evaluated.The cross spectrum and resisance mechanisms were investigated in the selected emamectin benzoate resistance strain(SCD-EB).This work could provide some theoretical basis for the adaptive resistance management of emamectin benzoate on the cotton bollworm.1.Resistance monitoring to three insecticides in H.armigeraBy the leaf-dip bioassay,the toxicities of emamectin benzoate,cyhalothrin and phoxim to the 14 field populations from different cotton planting area in 2014 were determined.In these three insecticedes,emamectin benzoate has the highest toxicity with LC500.0002-0.002mg/L,phoxim and cyhahothrin have the same range toxicity with LC501.4-34.0mg/L.Compared with the lab susceptible strain SCD,all 14 populations are sensitive to emamectin benzoate,there are only three populations from Huanghe River cotton region with higher LC50 value than SCD strain and the XJ population has the highest difference with 4.4-fold.The resistance level to phoxim are in the range of 2 to 7-fold in these 14 population and there is no difference between those populaions from different cotton region.The resistance level to cyhalothrin are from 6-fold to 25-fold,only 4 populations show the low level resistance and the others have the middle level resistance(>10-fold).Based on the results,these three insecticides could be used in the cotton field for the control of H.armigera,but they must obey some rules,such as in the early cotton season no use of insecticide and in the late cotton season rotation of insectides and limit use of pyrethroid in the Bt cotton field.All these scientifical and reasonable use of insecticide could prevent the development of resistance.2.Realized heritability,cross-resistance pattern and inheritance of resistance to emamection benzoate in H.armigeraIn the laboratory,SCD strain was continuously selected by emamectin benzoate.After 18 generations,the selected strain,SCD-EB,has 8-fold resistance to emamectin benzoate and 66-fold resistance compared with the other lab susceptible strain SW2012.By using the threshold trait analysis,the realized heritability(h2)is 0.067 and the reaction quotient Q is 0.043.It requires 20 generations to obtain 10-fold resistance to emamectin benzoate in H.armigera at 70%mortality.It means that H.armigera could develop resistance under the intensive use of emamectin benzoate.When the SCD-EB has 8-fold resistance to emamectin benzoate,it could have 2-fold cross-resistance to Abamectin,Fenvalerate and Chlorfenapyr and no resistance to Spinosad and Profenofos.The SCD-EB strain and SW2012 strain were used for reciprocal crosses.The LD50S of F1 are similar and the dominance levels of F1 are 0.302 and 0.253.The results means the resistance to emamectin benzoate in SCD-EB is incompletely dominant and autosomal.3.Biochemical mechanisms of resistance to emamectin benzoate in SCD-EBThe biochemical mechanisms of resistance to emamectin benzoate in SCD-EB were investigated by synergistic bioassay and metabolic enzyme activity detection.In SCD-EB strain,these three inhibitors of metabolic enzymes(PBO,DEF,DEM)and the ABC transporter inhibitor(Verapamil)could have 4-,5-fold synergism to emamectin benzoate.The synergism is 2-,3-fold in SCD strain and no synergism in SW2012.The activities of GST and esterase in SCD-EB,SCD and SW2012 are no difference.The PNOD activities of cytochrome P450 monooxygenase of SCD-EB and SCD have 8-fold and 9-fold increase compared with that of the SW2012,but between these two strains the activity is similar.These results indicate that the inhibitors of detoxify enzyme and ABC transporter protein have synergism to emamectin benzoate and the synergism increases along with the increase of resistance level.But the metabolic enzyme activity assays fail to show the relationship between metabolism and resistance,maybe the insufficiency of the substrate and the genetic background of the strains and so on.