Abstract
Susceptibility of various populations of the diamondback moth, Plutella xylostella LINNE, to fenvalerate was determined using fourth instar larvae by a topical application method. This survey revealed a high level of resistance to fenvalerate in several populations collected in 1984 in the southern part of Kyushu and on Okinawa Island and in populations collected in the southern part of the Japanese mainland in 1985 one or two years after the introduction of fenvalerate. The high pyrethroid-resistant populations, which had previously exhibited high resistance to organophosphorus or carbamate insecticides, also showed a high level of resistance to some combinations of fenvalerate and organophosphorus or carbamate insecticides. Although pyrethroid-resistant populations showed a high level of cross-resistance to all pyrethroides tested, the resistance level to permethrin was rather low. Synergistic activity of piperonyl butoxide with fenvalerate was low for the susceptible strain, but high for pyrethroid-resistant populations. The results suggested that microsomal oxidative metabolism contributed to pyrethroid resistance in this insect.
