The planthopper Laodelphax striatellus (Fallén) (Hemiptera: Delphacidae) is a serious insect pest of rice, Oryza sativa L., and has developed resistance to fipronil in Japan. Sequence analysis of L. striatellus RDL γ-aminobutyric acid (GABA) receptor subunit (LS-RDL) genes from a fipronilresistant population and a fipronil-susceptible strain identified the A2′N mutation (index number for M2 membrane-spanning region), that was previously implicated in fipronil resistance in the planthopper Sogatella furcifera (Horváth) (Hemiptera: Delphacidae). Nineteen of 21 fipronil-resistant L. striatellus individuals were genotyped as heterozygous for the A2′N mutation, suggesting that this mutation is associated with fipronil resistance and that most fipronil-resistant L. striatellus express wild-type and A2′N mutant LS-RDL simultaneously. To confirm the role of the A2′N mutation of LS-RDL, Drosophila Mel-2 cells were transfected with wild-type and A2′N mutant LS-RDL genes, either individually or together. A membrane potential assay showed that fipronil had no inhibitory effect at 10 μM on cells transfected with the A2′N mutant LS-RDL gene with or without the wild-type LS-RDL gene. By contrast, the IC50 value of fipronil for wild-type LS-RDL homomers was 14 nM. These results suggest that the A2′N mutation of the RDL GABA receptor subunit confers fipronil resistance in L. striatellus as well as S. furcifera.
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Vol. 104 • No. 2