Insecticide resistance spectrum and underlying resistance mechanisms in tropical populations of the brown planthopper (Nilaparvata lugens) collected from rice and the wild grass Leersia hexandra.

Two sibling species of Nilaparvata lugens sensu lato were collected from cultivated rice (Oryza sativa) and two from the wild grass Leersia hexandra . Strains of the rice-associated species of N. lugens were from populations exposed to insecticide selection pressure over an extended period, while the Leersia -associated species had little prior insecticide exposure. The rice-associated species from Batalagoda, Sri Lanka and Sulawesi, Indonesia both showed low (2- 5-fold) levels of resistance to malathion and propoxur, as measured by increased times to knock-down, and 2- 17-fold resistance to permethrin at the LT50 level compared with the Leersia -associated species from Bogor, Indonesia. The Goan Leersia -associated species had similar levels of susceptibility to malathion, but significantly lower susceptibility to permethrin than the Bogor one. Resistance in the Sri Lankan rice strain of N. lugens increased significantly after malathion selection in the laboratory. The major insecticide resistance mechanism in the two rice-associated strains was based on elevation of esterase activity. A highly elevated esterase electromorph was visible on native polyacrylamide gels of crude homogenates of these strains compared with those from Leersia . The diffuse nature of the esterase band suggested that it may contain more than one electromorph, but a range of electrophoretic techniques failed to differentiate more than one variant. Esterase activity increased after insecticide selection of the Sri Lankan rice-associated strain, while no effect on other possible resistance-associated enzyme systems was observed. The increased level of permethrin tolerance in the Goan Leersia strain was synergized by the monooxygenase inhibitor piperonyl butoxide. This synergist had no effect on the toxicity of permethrin or propoxur to the Sri Lankan rice-associated strain of N. lugens . There was no evidence of altered acetylcholinesterase or glutathione S -transferase based resistance mechanisms in any of the strains tested. [ABSTRACT FROM AUTHOR]