Resistance Patterns in the Rice Brown Planthopper, Nilaparvata lugens STÅL (Hemiptera

A rice brown planthopper population (T population) collected in rice fields of Takamatsu City, Kagawa Prefecture in October 1979 was selected in the laboratory with carbaryl or propoxur for 12 successive generations. Compared with the initial LD50 levels of the parent population (T population), the carbaryl-selected strain (Rc) developed a 4-fold resistance to carbaryl, 2 to 4-fold resistance to most of the carbamates tested and also to the organophosphorus insecticides, dimethylvinphos, tetrachlorvinphos, monocrotophos, propaphos, fenthion, pyridaphenthion, EPN, disulfoton, malathion, dimethoate, phenthoate and mecarbam while the susceptibility to diazinon, cyanofenphos and isoxathion remained unchanged. The propoxur-selected strain (Rp) acquired a 5-fold resistance to propoxur, 2- to 4-fold resistance to the other carbamates tested and 2- to 11-fold resistance to dimethylvinphos, propaphos, isoxathion, EPN, disulfoton, malathion, dimethoate, phenthoate and mecarbam while the LD50 for monocrotophos, fenthion, fenitrothion remained practically unchanged. The two selected strains were slightly less susceptible to pyrethrins and organophosphorus fungicides such as IBP and edifenphos. Rc and Rp strains showed a resistance pattern relatively similar to that of the T population, indicating that resistance factor(s) did not vary during the 12 generations when the rice brown planthopper population which had acquired a certain level of organophosphorus and carbamate resistance was continuously selected with carbaryl or propoxur.