Resistance Spectrum to Various Insecticides in the Diamondback Moth, Plutella xylostella LINNÉ (Lepidoptera: Yponomeutidae)

Abstract

Susceptibility of 31 populations of the diamondback moth, Plutella xylostella, to various insecticides collected all over Japan was determined in 4th instar larvae by using the topical application method. Pyrethroids were the most toxic to a susceptible strain (S), followed by organophosphate such as cyanofenphos, dimethylvinphos, methidathion, and so on. Large variations of insecticidal activity were observed among 23 organophosphorus insecticides (OP). Methomyl, cartap, thiocyclam and DDT exhibited a moderate toxicity to the S strain. A moderate decrease in susceptibility to fenvalerate was observed in the Naha population. The Yokota population which was susceptible to pyrethroids and resistant to OP exhibited a high resistance to DDT. A moderate resistance to cartap and thiocyclam was observed. Resistance levels of populations to OP and carbamate insecticides were extremely different. Based on their resistance spectra, the 31 populations could be divided into five groups. Resistance spectra of each group were similar to one another, i.e., resistance levels of each group were higher to cyanofenphos, prothiofos, cyanophos and isoxathion than to dimethylvinphos, methidathion and profenofos. Resistance levels to OP were low in Hokkaido, whereas high in the southern part of Kyushu and Okinawa. A moderate OP resistance distributed from the Tohoku district to the northern part of Kyushu. Seasonal changes of the resistance level to OP were observed in Hokkaido, Gunma and Shimane where the resistance level was lower in spring and in early summer and higher in autumn.