title: Biochemical and molecular characterisation and cross-resistance in field and laboratory chlorpyrifos-resistant strains of Laodelphax striatellus (Hemiptera: Delphacidae) from eastern China.
abstract: BACKGROUND
  Laboratory selection is often employed in resistance mechanism studies because field-derived populations commonly do not have high enough resistance for such studies. In the present study, a field-collected Laodelphax striatellus population from eastern China was laboratory selected for chlorpyrifos resistance and susceptibility, and the developed strains, along with a field population, were studied for cross-resistance and resistance mechanisms at biochemical and molecular levels.
  
  
  RESULTS
  A 158.58-fold chlorpyrifos-resistant strain (JH-chl) and a chlorpyrifos-susceptible strain (JHS) were established after laboratory selection of 25 generations. Cross-resistance to deltamethrin, diazinon, methomyl, carbosulfan, acephate and imidacloprid were detected in JH-chl and a field-collected strain (JHF). Synergism and enzyme activity data suggested potential involvement of P450s and esterases in JH-chl as well as AChE alteration. Furthermore, CYP6AY3v2, CYP306A2v2, CYP353D1v2 and LSCE36 genes were significantly overexpressed in JH-chl (6.87-12.14-fold). Feeding of dsRNAs reduced the expression of the four target genes (35.6-56.8%) and caused significant adult mortality (75.21-88.45%), implying resistance reduction. However, mechanism(s) conferring chlorpyrifos resistance in JHF were unclear.
  
  
  CONCLUSIONS
  In contrast to previous reports, multiple overexpressed detoxification genes were potentially associated with chlorpyrifos resistance, as confirmed by RNAi feeding tests. Chlorpyrifos resistance exhibits cross-resistance with insecticides in the same and different classes.
authors.affiliation: Education Ministry Key Laboratory of Integrated Management of Crop Diseases and Pests, College of Plant Protection, Nanjing Agricultural University, Nanjing, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Xu
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Zhaojun
authors.initials: Z
authors.lastname: Han
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002681:China; D004390:Chlorpyrifos / Q000494:pharmacology*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D006430:Hemiptera / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism; D007305:Insecticide Resistance; D007306:Insecticides / Q000494:pharmacology*; D007928:Lethal Dose 50; D008969:Molecular Sequence Data; D034622:RNA Interference; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D012621:Seasons
chemical_list: D019476:Insect Proteins; D007306:Insecticides; D012333:RNA, Messenger; D003577:Cytochrome P-450 Enzyme System; D004390:Chlorpyrifos
keywords: P450; RNAi; acetylcholinesterase; esterases; quantitative real-time RT-PCR; semi-quantitative RT-PCR; small brown planthopper