A malathion-resistant strain of Nilaparvata lugens (Stål) developed in the laboratory by continuous selection of a field strain for nine generations gained 1,183-fold resistance as compared with a susceptible strain. An MIPC-resistant strain selected similarly for 16 generations developed 41-fold resistance. Both were equally and significantly resistant to propoxur and permethrin while remaining susceptible to fenvalerate. Field strains from heavily treated areas showed similar patterns of resistance to these chemicals.