| The small brown planthopper(SBPH),Laodelphax striatellus(Fallen)has a wide distribution ranging from south-east Asia to Siberia and as far as Europe.It is an economically important phytophagous species in the family of Delphacidae,which attacts several important agricultural crops,including rice,corn,wheat,oat and barley.L.striatellus has been control]ed by insecticides.Unfortunately,the loncg-term and extensive spraying of insecticides has led to its resistance.To delay the resistance,it is necessary to declear the occurrence mechanism.In this study,correspondingly based on Deltamethrin and Imidacloprid resistant strains,the Chlorpyrifos-resistant strain was developed through selections generation by generation.We monitored its periodic resistance level,and the potential related P450 genes,esterase gene,and ABC transpoter genes have been selected by Chlorpyrifos selection.All these will provide a theoretical basis to clarify the evolution mechanism of Chlorpytrifos-resistance in L.striatellus.1.Effects of chlorpyrifos selection on the resistance evolution of Laodelphax striatellusWith the method of spra)ying on both rice and insects,chlorp)yrifos was used to select for resistance with either deltamethrin-resistant strain and imidacloprid-resistant strain as original.Pesticide resistance monitoring results showed that if novel sensitive insecticides were used for selection,the resistance development won’t be speeded up by using a resistant population as the original.When chlorpyrifos treatment led to middle-level(10-12 fold)resistance to Chlorpyrifos,cross-resistance to Deltamethrin and Imidacloprid was also found increased significantly up to 3 fold,which validate that cross-resistance exist between chlorpyrifos,deltamethrin and imidacloprid.While we made chlorpyrifos resistance strain in natural recession,its sensitivity for the three different pesticides were all recovered.However,the recovery speeds varied with resistant strains having different insecticide treatment backgrounds.The strain(R-Del 13)developed by selecting deltamethrin resistant strain showed faster susceptibility recovery for deltamethrin,but lower for chlorpyrifos.The strain(R-Imil3)developed by selecting imidacloprid resistant strain showed also different susceptibility recovery speed for different insecticides,with the order as:chlorpyrifos>deltamethrin>imidacloprid.The results will provide a theoretical basis of rotation use of insecticides in control of L.strialellus in fields2.The correlation of chlorpyrifos resistance with P450 genes in L.striatellusNine P450 genes had been identified prexviously in our laboratory as resistance-related genes,In the present work,we test all related genes in various strains produced during resistance selection and recovery.The results showed with deltamethrin-resistant strain as original,the expression of CYP353D1v2,CYP4C72,CYP439A1v3,CYP6AY3v2,CYPC71v2 and CYP6FU1 has a synchronization relationship with the development of chlorpyrifos resistence.With imidacloprid-resistant strain as original,the relationship between chlorpyrifos resistence and the five P450genes,CYPC71v2.CYP314A1v2,CYP6AY3v2,CYP6FU1 and CYP353D1v2.is closely bounded.Comparing these two selection methods,whatever origin it comes from.CYP64Y31v2,CYP353D1v2,CYPC71v2 and CYP6FU1 play a significant role in the constant resistance,which implies that that over-expression of these genes can improve planthopper’s resistance to different pesticides.By reference to CYP306A2v2 and CYP4C71v2,they show little correlation with resistance,which infers these two genes had no significant relationship with the planthopper’s resistance.The rest three P450 genes can respectively be linked to some pesticide resistance.CYP4C72 and CYP439Av3 are relative to chlorpyrifos resistence with deltamethrin-resistant strain as original,and CYP314A1v2 is only relative to chlorpyrifos resistence with original deltamethrin-resistant strain.All these attribute to the conclusion that previous medication history can affect the development of resistance in Laodelphax striatellus.3.The correlation of chlorpyrifos resistance with carboxylesterase and ABC genes in L.striatellusTwo carboxylesterase and seventeen ABC genes had been identified previously in our laboratory as resistance-related genes.In the present work,we test all related genes in various strains produced during resistance selection and recovery.The results showed as follows.The monitoring of two associated esterase genes LsCE12 and LsCE35 show that their expression climb directly up as its developed resistance no matter which original strains they come from,which implies that that over-expression of these genes can improve planthopper’s resistance to different pesticides.With deltamethrin-resistant strain as original,the expression levels of G10,B2,H5,H6 significantly up-regulated in deltamethrin-resistant strain,and the expression ratios were 1.59-,7.03-,42.01-and 18.34 fold.To the original imidacloprid-resistance strain,the expression levels of G11 and H6 significantly up-regulated in deltamethrin-resistant strain,and climbed as much as 23 and 28 times relatively than sensitive strains.As to the whole selection,the natural recession also included,the expression of LsCE12,LsCE35,and ABC family-H6 declined with the same way of falling resistance. |
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