RESUMO
The beetle Oulema oryzae Kuwayama (Coleoptera: Chrysomelidae), an important pest of rice, has developed fipronil resistance in Japan. Molecular cloning and sequence analysis of O. oryzae RDL gamma-aminobutyric acid (GABA) receptor subunit (OO-RDL) genes from fipronil-susceptible and -resistant O. oryzae identified the A2'S mutation (index number for the M2 membrane-spanning region). To investigate the effect of the A2'S mutation on fipronil resistance, we stably expressed the wild-type and mutant OO-RDL homomers in Drosophila Mel-2 cells. A membrane potential assay exhibited that the IC50 values of fipronil for inhibition of the response to EC80 GABA of the wild-type and A2'S mutant OO-RDL homomers were 0.09 microM and 0.11 microM, respectively. However, the IC50 values of fipronil for inhibition of the response to EC95 GABA of the wild-type and A2'S mutant OO-RDL homomers were 0.11 microM and approximately equal to 5 microM, respectively. These results suggest that the GABA concentration is an important factor affecting fipronil resistance in O. oryzae carrying the A2'S mutation in OO-RDL.
Assuntos
Besouros/genética , Proteínas de Insetos/genética , Resistência a Inseticidas/genética , Inseticidas/farmacologia , Pirazóis/farmacologia , Receptores de GABA/genética , Sequência de Aminoácidos , Animais , Besouros/efeitos dos fármacos , Drosophila , Proteínas de Drosophila/genética , Potenciais da Membrana , Dados de Sequência Molecular , Mutação , Reação em Cadeia da Polimerase Via Transcriptase Reversa , TransfecçãoRESUMO
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 gamma-aminobutyric acid (GABA) receptor subunit (LS-RDL) genes from a fipronil-resistant 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 microM 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.
