Pyrethroid Resistance and Synergism in Nilaparvata lugens Stål (Homoptera: Delphacidae) in Taiwan

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Abstract
Permethrin and several other pyrethroids with a primary alcohol ester were much less toxic to Nilaparvata lugens Stål than pyrethroids with a secondary alcohol ester. Field strains of N. lugens resistant to many organophosphorus and carbamate insecticides developed much higher resistance to pyrethroids without an α-cyano group. Permethrin, phenothrin, and fenpropathrin were synergized by piperonyl butoxide and S,S,S-tributyl phosphorotrithioate in the resistant strains, while only phenothrin was synergized in the susceptible strain. Cypermethrin was synergized only to a very limited extent, thus suggesting limited metabolism in these strains. The recovery of both susceptible and resistant N. lugens knocked down by permethrin was also reduced by both synergists. High esterase activity associated with organophosphorus and carbamate resistance in N. lugens may have conferred a major part of the resistance to permethrin and other primary alcohol ester pyrethroids. In addition, the ester linkage of these pyrethroids without an α-cyano group might be vulnerable to oxidative cleavage.