抄録
The long-term change of the susceptibility of the brown planthopper to 8 widely used insecticides were estimated by micro-topical application technique. The LD50 values obtained in 1975-1976 were comparedwith the values obtained in 1967 to determine if insecticide resistance developed during these 9 years making reference to the change of susceptibilities of the white backed planthopper and the small brown planthopper during the corresponding period.The results revealed development of resistance in the brown planthopper to organophosphates, especially to malathion by ca. 10 times of increase of LD50 over the last 9 years and susceptibility to the carbamates also decreased slightly. However, the white backed planthopper showed virtually no change in LD50 during the period.The small broewn planthopper increased susceptibility to BHC and developed remarkable resistance to malathion and fenitrothion. They also developed slight resistance to the carbamates.
